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@Book { 457,
title = {Color Vision: From Genes to Perception},
year = {1999},
pages = {492},
department = {Department B{\"u}lthoff},
web_url = {http://www.allpsych.uni-giessen.de/karl/colbook/index.html},
publisher = {Cambridge University Press},
address = {Cambridge, UK},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
language = {en},
ISBN = {0-521-59053-1},
author = {Gegenfurtner, KR and Sharpe, LT}
}
@Proceedings { 2358,
title = {6. T{\"u}binger Wahrnehmungskonferenz},
journal = {Proceedings of the 6. T{\"u}binger Wahrnehmungskonferenz (TWK 2003)},
year = {2003},
month = {2},
pages = {183},
url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/pdf2358.pdf},
department = {Department B{\"u}lthoff},
web_url = {http://www.twk.tuebingen.mpg.de/twk03/},
publisher = {Knirsch},
address = {Kirchentellinsfurt, Germany},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {T{\"u}bingen, Germany},
event_name = {Sixth Perception Conference at T{\"u}bingen (TWK 2003)},
language = {en},
ISBN = {3-927091-62-6},
author = {B{\"u}lthoff, HH and Gegenfurtner, K and Mallot, HA and Ulrich, R and Wichmann, FA}
}
@Proceedings { 1209,
title = {TWK 2002 : Beitr{\"a}ge zur 5. T{\"u}binger Wahrnehmungskonferenz},
journal = {Proceedings of the 5. T{\"u}binger Wahrnehmungskonferenz (TWK 2002)},
year = {2002},
month = {2},
pages = {222},
url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/pdf1209.pdf},
department = {Department B{\"u}lthoff},
web_url = {http://www.twk.tuebingen.mpg.de/twk02/},
publisher = {Knirsch},
address = {Kirchentellinsfurt, Germany},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {T{\"u}bingen, Germany},
event_name = {5. T{\"u}binger Wahrnehmungskonferenz (TWK 2002)},
language = {en},
ISBN = {3-927091-56-1},
author = {B{\"u}lthoff, HH and Gegenfurtner, K and Mallot, HA and Ulrich, R}
}
@Proceedings { 666,
title = {TWK 2001: Beitr{\"a}ge zur 4. T{\"u}binger Wahrnehmungskonferenz},
journal = {Proceedings of the 4. T{\"u}binger Wahrnehmungskonferenz (TWK 2001)},
year = {2001},
month = {3},
pages = {184},
url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/pdf666.pdf},
department = {Department B{\"u}lthoff},
web_url = {http://www.twk.tuebingen.mpg.de/twk01/TWK.pdf},
publisher = {Knirsch},
address = {Kirchentellinsfurt, Germany},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {T{\"u}bingen},
event_name = {4. T{\"u}binger Wahrnehmungskonferenz (TWK 2001)},
language = {en},
ISBN = {3-927091-54-5},
author = {B{\"u}lthoff, HH and Gegenfurtner, K and Mallot, HA and Ulrich, R}
}
@Proceedings { 173,
title = {TWK 2000: Beitr{\"a}ge zur 3. T{\"u}binger Wahrnehmungskonferenz},
journal = {Proceedings of the 3. T{\"u}binger Wahrnehmungskonferenz (TWK 2000)},
year = {2000},
month = {2},
pages = {169},
url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/pdf173.pdf},
department = {Department B{\"u}lthoff},
web_url = {http://www.twk.tuebingen.mpg.de/twk00/TWK.pdf},
publisher = {Knirsch},
address = {Kirchentellinsfurt, Germany},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {T{\"u}bingen, Germany},
event_name = {3. T{\"u}binger Wahrnehmungskonferenz (TWK 2000)},
language = {en},
ISBN = {3-927091-49-9},
author = {B{\"u}lthoff, HH and Fahle, M and Gegenfurtner, K and Mallot, HA}
}
@Proceedings { 455,
title = {Beitr{\"a}ge zur 2. T{\"u}binger Wahrnehmungskonferenz},
journal = {Proceedings of the 2. T{\"u}binger Wahrnehmungskonferenz (TWK 1999)},
year = {1999},
month = {2},
pages = {134},
url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/pdf455.pdf},
department = {Department B{\"u}lthoff},
web_url = {http://www.twk.tuebingen.mpg.de/twk99/},
publisher = {Knirsch},
address = {Kirchentellinsfurt, Germany},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {T{\"u}bingen, Germany},
event_name = {2. T{\"u}binger Wahrnehmungskonferenz (TWK 99)},
language = {en},
ISBN = {3-927091-45-6},
author = {B{\"u}lthoff, HH and Fahle, M and Gegenfurtner, K and Mallot, HA}
}
@Proceedings { 665,
title = {Visuelle Wahrnehmung: Beitr{\"a}ge zur 1. T{\"u}binger Wahrnehmungskonferenz},
journal = {Proceedings of the 1. T{\"u}binger Wahrnehmungskonferenz (TWK 1998)},
year = {1998},
month = {2},
pages = {170},
url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/pdf665.pdf},
department = {Department B{\"u}lthoff},
web_url = {http://www.twk.tuebingen.mpg.de/twk98/},
publisher = {Knirsch},
address = {Kirchentellinsfurt, Germany},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {T{\"u}bingen, Germany},
event_name = {1. T{\"u}binger Wahrnehmungskonferenz (TWK 1998)},
language = {en},
ISBN = {3-927091-40-5},
author = {B{\"u}lthoff, HH and Fahle, M and Gegenfurtner, K and Mallot, HA}
}
@Article { 3551,
title = {Phase noise and the classification of natural images},
journal = {Vision Research},
year = {2006},
month = {4},
volume = {46},
number = {8-9},
pages = {1520-1529},
abstract = {We measured the effect of global phase manipulations on a rapid animal categorization
task. The Fourier spectra of our images of natural scenes were manipulated by adding
zero-mean random phase noise at all spatial frequencies. The phase noise was the
independent variable, uniformly and symmetrically distributed between 0 degree and
±180 degrees. Subjects were remarkably resistant to phase noise. Even with ±120 degree
phase noise subjects were still performing at 75\% correct. The high resistance of the
subjects animal categorization rate to phase noise suggests that the visual system is
highly robust to such random image changes. The proportion of correct answers closely
followed the correlation between original and the phase noise-distorted images. Animal
detection rate was higher when the same task was performed with contrast reduced
versions of the same natural images, at contrasts where the contrast reduction mimicked
that resulting from our phase randomization. Since the subjects categorization rate was
better in the contrast experiment, reduction of local contrast alone cannot explain the
performance in the phase noise experiment. This result obtained with natural images
differs from those obtained for simple sinusoidal stimuli were performance changes due
to phase changes are attributed to local contrast changes only. Thus the global phasechange
accompanying disruption of image structure such as edges and object boundaries
at different spatial scales reduces object classification over and above the performance
deficit resulting from reducing contrast. Additional colour information improves the categorization performance by 2 \%.},
url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/Wichmann_etal_2006_3551[0].pdf},
department = {Department Sch{\"o}lkopf},
web_url = {http://www.sciencedirect.com/science?_ob=MImg\&_imagekey=B6T0W-4HWXNXP-2-H\&_cdi=4873\&_user=29041\&_orig=browse\&_coverDate=04\%2F30\%2F2006\&_sk=999539991\&view=c\&wchp=dGLbVtb-zSkzk\&md5=3f22537faf1eb6e23cbb263518a309c4\&ie=},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
language = {en},
DOI = {10.1016/j.visres.2005.11.008},
author = {Wichmann, FA and Braun, DI and Gegenfurtner, KR}
}
@Article { 3341,
title = {The dynamics of visual pattern masking in natural scene processing: A magnetoencephalography study},
journal = {Journal of Vision},
year = {2005},
month = {3},
volume = {5},
number = {3},
pages = {275-286},
abstract = {We investigated the dynamics of natural scene processing and mechanisms of pattern masking in a scene-recognition task. Psychophysical recognition performance and the magnetoencephalogram (MEG) were recorded simultaneously. Photographs of natural scenes were briefly displayed and in the masked condition immediately followed by a pattern mask. Viewing the scenes without masking elicited a transient occipital activation that started approximately 70 ms after the pattern onset, peaked at 110 ms, and ended after 170 ms. When a mask followed the target an additional transient could be reliably identified in the MEG traces. We assessed psychophysical performance levels at different latencies of this transient. Recognition rates were reduced only when the additional activation produced by the pattern mask overlapped with the initial 170 ms of occipital activation from the target. Our results are commensurate with an early cortical locus of pattern masking and indicate that 90 ms of undistorted cortical processing is necessary to reliably recognize a scene. Our data also indicate that as little as 20 ms of undistorted processing is sufficient for above-chance discrimination of a scene from a distracter.},
url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/Rieger-2005-jov-5-3-10_3341[0].pdf},
department = {Department B{\"u}lthoff},
web_url = {http://journalofvision.org/5/3/10/},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
language = {en},
DOI = {10.1167/5.3.10},
author = {Rieger, J and Braun, C and B{\"u}lthoff, HH and Gegenfurtner, K}
}
@Article { 1136,
title = {The contributions of color to recognition memory for natural scenes},
journal = {Journal of Experimental Psychology: Learning, Memory and Cognition},
year = {2002},
month = {5},
volume = {28},
number = {3},
pages = {509-520},
abstract = {The authors used a recognition memory paradigm to assess the influence of color information on visual memory for images of natural scenes. Subjects performed 5-10\% better for colored than for black-and-white images independent of exposure duration. Experiment 2 indicated little influence of contrast once the images were suprathreshold, and Experiment 3 revealed that performance worsened when images were presented in color and tested in black and white, or vice versa, leading to the conclusion that the surface property color is part of the memory representation. Experiments 4 and 5 exclude the possibility that the superior recognition memory for colored images results solely from attentional factors or saliency. Finally, the recognition memory advantage disappears for falsely colored images of natural scenes: The improvement in recognition memory depends on the color congruence of presented images with learned knowledge about the color gamut found within natural scenes. The results can be accounted for within a multiple memory systems framework.},
url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/pdf1136.pdf},
department = {Department B{\"u}lthoff},
department2 = {Department Sch{\"o}lkopf},
web_url = {http://psycnet.apa.org/journals/xlm/28/3/509/},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
DOI = {10.1037/0278-7393.28.3.509},
author = {Wichmann, FA and Sharpe, LT and Gegenfurtner, KR}
}
@Article { 36,
title = {Effects of visual illusions on grasping},
journal = {Journal of Experimental Psychology: Human Perception and Performance},
year = {2001},
month = {10},
volume = {27},
number = {5},
pages = {1124-1144},
abstract = {In 2 experiments, the Muller-Lyer illusion (F. C. Muller-Lyer, 1889; N = 16) and the parallel-lines illusion (W. Wundt, 1898; N = 26) clearly
affected maximum preshape aperture in grasping (both ps < .001). The grasping effects were similar but not perfectly equal to the perceptual effects. Control
experiments show that these differences can be attributed to problems in matching the perceptual task and the grasping task. A model is described stating the
assumptions that are needed to compare the grasping effects and the perceptual effects of visual illusions. Further studies on the relationship between
perception and grasping are reviewed. These studies provide no clear evidence for a dissociation between perception and grasping and therefore do not
support the action versus perception hypothesis (A. D. Milner \& M. A. Goodale, 1995).},
url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/effects_of_visual_illusions_on_grasping_36[0].pdf},
department = {Department B{\"u}lthoff},
web_url = {http://psycnet.apa.org/journals/xhp/27/5/1124.pdf},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
DOI = {10.1037/0096-1523.27.5.1124},
author = {Franz, V and Fahle, M and B{\"u}lthoff, HH and Gegenfurtner, K}
}
@Article { 51,
title = {Detection of animals in natural images using far peripheral vision},
journal = {European Journal of Neuroscience},
year = {2001},
month = {9},
volume = {14},
number = {5},
pages = {869-876},
abstract = {It is generally believed that the acuity of the peripheral visual field is too poor to allow accurate object recognition and, that to be identified, most
objects need to be brought into foveal vision by using saccadic eye movements. However, most measures of form vision in the periphery have been done at
eccentricities below 10 degrees and have used relatively artificial stimuli such as letters, digits and compound Gabor patterns. Little is known about how such
data would apply in the case of more naturalistic stimuli. Here humans were required to categorize briefly flashed (28 ms) unmasked photographs of natural
scenes (39 degrees high, and 26 degrees across) on the basis of whether or not they contained an animal. The photographs appeared randomly in nine
locations across virtually the entire extent of the horizontal visual field. Accuracy was 93.3\% for central vision and decreased almost linearly with increasing
eccentricity (89.8\% at 13 degrees, 76.1\% at 44.5 degrees and 71.2\% at 57.5 degrees). Even at the most extreme eccentricity, where the images were
centred at 70.5 degrees, subjects scored 60.5\% correct. No evidence was found for hemispheric specialization. This level of performance was achieved
despite the fact that the position of the image was unpredictable, ruling out the use of precued attention to target locations. The results demonstrate that even
high-level visual tasks involving object vision can be performed using the relatively coarse information provided by the peripheral retina.},
url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/pdf51.pdf},
department = {Department B{\"u}lthoff},
web_url = {http://onlinelibrary.wiley.com/doi/10.1046/j.0953-816x.2001.01717.x/pdf},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
DOI = {10.1046/j.0953-816x.2001.01717.x},
author = {Thorpe, SJ and Gegenfurtner, KR and Fabre-Thorpe, M and B{\"u}lthoff, HH}
}
@Article { 1435,
title = {Velocity constancy in a virtual reality environment},
journal = {Perception},
year = {2000},
month = {12},
volume = {29},
number = {12},
pages = {1423-1435},
abstract = {During everyday life the brain is continuously integrating multiple perceptual cues in order to allow us to make decisions and to guide our actions. In this study we have used a simulated (virtual reality -- VR) visual environment to investigate how cues to speed judgments are integrated. There are two sources that could be used to provide signals for velocity-constancy, temporal-frequency, or distance cues. However, evidence from most psychophysical studies favour temporal-frequency cues. Here we report that two depth cues that provide a relative object - object distance, disparity, and motion parallax, can provide a significant input to velocity-constancy judgments, particularly when combined. This result indicates that the second mechanism can also play a significant role in generating velocity constancy. Furthermore, we show that cognitive factors such as familiar size can influence the perception of object speed. The results suggest that both low-level cues to spatiotemporal structure and depth, and high-level cues, such as object familiarity, are integrated by the brain during velocity estimation in real-world viewing.},
url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/pdf1435.pdf},
department = {Department B{\"u}lthoff},
web_url = {http://www.perceptionweb.com/abstract.cgi?id=p3115},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
DOI = {10.1068/p3115},
author = {Distler, H and Gegenfurtner, KR and van Veen, HAHC and Hawken, MJ}
}
@Article { 84,
title = {Motion perception at scotopic light levels},
journal = {Journal of the Optical Society of America A: Optics Image Science and Vision},
year = {2000},
month = {9},
volume = {17},
number = {9},
pages = {1505-1515},
abstract = {Although the spatial and temporal properties of rod-mediated vision have been extensively characterized, little is known about scotopic motion perception. To provide such information, we determined thresholds for the detection and identification of the direction of motion of sinusoidal grating patches moving at speeds from 1 to 32 deg/s, under scotopic light levels, in four different types of observers: three normals, a rod monochromat (who lacks all cone vision), an S-cone monochromat (who lacks M- and L-cone vision), and four deuteranopes (who lack M-cone vision). The deuteranopes, whose motion perception does not differ from that of normals, allowed us to measure rod and L-cone thresholds under silent substitution conditions and to compare directly the perceived velocity for moving stimuli detected by either rod or cone vision at the same light level. We find, for rod as for cone vision, that the direction of motion can be reliably identified very near to detection threshold. In contrast, the perceived velocity of rod-mediated stimuli is reduced by approximately 20\% relative to cone-mediated stimuli at temporal frequencies below 4 Hz and at all intensity levels investigated (0.92 to −1.12 log cd m−2). Most likely, the difference in velocity perception is distal in origin because rod and cone signals converge in the retina and further processing of their combined signals in the visual cortex is presumably identical. To account for the difference, we propose a model of velocity, in which the greater temporal averaging of rod signals in the retina leads to an attenuation of the motion signal in the detectors tuned to high velocities.},
url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/pdf84.pdf},
department = {Department B{\"u}lthoff},
web_url = {http://www.opticsinfobase.org/josaa/abstract.cfm?uri=josaa-17-9-1505},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
DOI = {10.1364/JOSAA.17.001505},
author = {Gegenfurtner, KR and Mayser, HM and Sharpe, LT}
}
@Article { 78,
title = {The colors seen behind transparent filters},
journal = {Perception},
year = {2000},
month = {8},
volume = {29},
number = {8},
pages = {911-926},
abstract = {How do the colors and lightnesses of surfaces seen to lie behind a transparent filter depend on the chromatic properties of the filter? A convergence model developed in prior work (D'Zmura et al, 1997 Perception 26 471 - 492; Chen and D'Zmura, 1998 Perception 27 595 - 608) suggests that the visual system interprets a filter's transformation of color in terms of a convergence in color space. Such a convergence is described by a color shift and a change in contrast. We tested the model using an asymmetric matching task. Observers adjusted, in computer graphic simulation, the color of a surface seen behind a transparent filter in order to match the color of a surface seen in plain view. The convergence model fits the color-matching results nearly as well as a more general affine-transformation model, even though the latter has many more parameters. Other models, including von Kries scaling, did not perform as well. These results suggest that the color constancy revealed in this task is described best by a model that takes into account both color shifts and changes in contrast.},
url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/pdf78.pdf},
department = {Department B{\"u}lthoff},
web_url = {http://www.perceptionweb.com/abstract.cgi?id=p2988},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
DOI = {10.1068/p2988},
author = {D'Zmura, M and Rinner, O and Gegenfurtner, KR}
}
@Article { 85,
title = {Sensory and cognitive contributions of color to the recognition of natural scenes},
journal = {Current Biology},
year = {2000},
month = {6},
volume = {10},
number = {13},
pages = {805-808},
abstract = {Although color plays a prominent part in our subjective experience of the visual world, the evolutionary advantage of color vision is still unclear [1] and [2], with most current answers pointing towards specialized uses, for example to detect ripe fruit amongst foliage [3], [4], [5] and [6]. We investigated whether color has a more general role in visual recognition by looking at the contribution of color to the encoding and retrieval processes involved in pattern recognition [7], [8] and [9]. Recognition accuracy was higher for color images of natural scenes than for luminance-matched black and white images, and color information contributed to both components of the recognition process. Initially, color leads to an image-coding advantage at the very early stages of sensory processing, most probably by easing the image-segmentation task. Later, color leads to an advantage in retrieval, presumably as the result of an enhanced image representation in memory due to the additional attribute. Our results ascribe color vision a general role in the processing of visual form, starting at the very earliest stages of analysis: color helps us to recognize things faster and to remember them better.},
url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/pdf85.pdf},
department = {Department B{\"u}lthoff},
web_url = {http://www.sciencedirect.com/science/article/pii/S0960982200005637},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
DOI = {10.1016/S0960-9822(00)00563-7},
author = {Gegenfurtner, KR and Rieger, JW}
}
@Article { 99,
title = {Time course of chromatic adaptation for color appearance and discrimination},
journal = {Vision Research},
year = {2000},
month = {6},
volume = {40},
number = {14},
pages = {1813-1826},
abstract = {Adaptation to a steady background has a profound effect on both color appearance and discrimination. We determined the temporal characteristics of chromatic adaptation for appearance and discrimination along different color directions. Subjects were adapted to a large uniform background made up of a CRT screen and a 45\(\times\)64\(^{\circ}\) wall, illuminated by computer controlled lamps. After an instant change in background color along a red–green or blue–yellow color axis, we measured thresholds for the detection of increments along the same axes at fixed times between 25 ms and 121 s. Analogously, color appearance was determined using achromatic matching. Three components of adaptation could be identified by their temporal characteristics. A slow exponential time course of adaptation with a half-life of about 20 s was common to appearance and discrimination. A faster component with a half-life of 40–70 ms — probably due to photoreceptor adaptation — was also common to both. Exclusive for color appearance, there was a third, extremely rapid mechanism with a half-life faster than 10 ms. This instantaneous process explained more than 50\% of total adaptation for color appearance and could be shown to act in a multiplicative manner. We conclude that this instantaneous adaptation mechanism for color appearance is situated at a later processing stage, after mechanisms common to appearance and discrimination, and is based on multiplicative spatial interactions rather than on local, temporal adaptational processes. Color appearance, and thus color constancy, seems to be determined in large part by cortical computations.},
url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/pdf99.pdf},
department = {Department B{\"u}lthoff},
web_url = {http://www.sciencedirect.com/science/article/pii/S004269890000050X},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
DOI = {10.1016/S0042-6989(00)00050-X},
author = {Rinner, O and Gegenfurtner, KR}
}
@Article { 80,
title = {Grasping visual illusions: No evidence for a dissociation between perception and action},
journal = {Psychological Science},
year = {2000},
month = {1},
volume = {11},
number = {1},
pages = {20-25},
abstract = {Neuropsychological studies prompted the theory
that the primate visual system might be organized
into two parallel pathways, one for conscious
perception and one for guiding action. Supporting
evidence in healthy subjects seemed to come from a
dissociation in visual illusions: In previous
studies, the Ebbinghaus (or Titchener) illusion
deceived perceptual judgments of size, but only
marginally influenced the size estimates used in
grasping. Contrary to those results, the findings
from the present study show that there is no
difference in the sizes of the perceptual and
grasp illusions if the perceptual and grasping
tasks are appropriately matched. We show that the
differences found previously can be accounted for
by a hitherto unknown , nonadditive effect in the
addition. We conclude that the illusion does not
provide evidence for the existence of two distinct
pathways for perception and action in the visual
system.},
url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/pdf80.pdf},
department = {Department B{\"u}lthoff},
web_url = {http://pss.sagepub.com/content/11/1/20.full.pdf},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
DOI = {10.1111/1467-9280.00209},
author = {Franz, VH and Gegenfurtner, KR and B{\"u}lthoff, HH and Fahle, M}
}
@Article { 191,
title = {Visual Perception: Reflections on colour constancy},
journal = {Nature},
year = {1999},
month = {12},
volume = {402},
number = {6764},
pages = {855-856},
abstract = {A study of colour perception shows that, when assigning colour to objects, the seeing brain takes into account subtle reflections of light between the surfaces in a scene.
For more than two centuries, scientists and artists have come up with a range of ways to demonstrate that the wavelength composition over a whole scene can affect how we perceive the colour of the individual parts of that scene. The proportion of light of each wavelength reflected from an object can be highly beneficial in detecting or recognizing objects1. However, to make use of that invariant, the visual system somehow has to discount the illuminating light, which can vary quite drastically.
This process is usually called 'colour constancy', and the degree to which it is shown depends on many factors. Some of them occur at the early stages of sensory processing2, such as local colour contrast, whereas others (for instance, colour memory) occur at higher cognitive levels3. Most computational schemes for achieving colour constancy try to decompose the overall light reaching the eye into one component that is due to the illuminant, and a second component due to the reflectance.
However, the physics of light is more complicated than the simple reflection of light from a surface into the eye, as if looking at a photograph. In a three-dimensional world, some light is reflected from one surface, but it then bounces to yet another surface from which it is reflected into the eye (Fig. 1). And so on. These indirect reflections are called 'inter-reflections', and are of especial interest to those involved in computer graphics and computer vision4. For example, computer simulations of indoor scenes appear more realistic when inter-reflections are taken into account. Indeed, many recent advances in computer graphics are due to the discovery of efficient algorithms to calculate the effects of all such multiple bounces of light among the vast number of surfaces typically contained in a scene.},
url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/pdf191.pdf},
department = {Department B{\"u}lthoff},
web_url = {http://www.nature.com/nature/journal/v402/n6764/pdf/402855a0.pdf},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
DOI = {10.1038/47194},
author = {Gegenfurtner, KR}
}
@Article { 211,
title = {Velocity tuned mechanisms in human motion processing},
journal = {Vision Research},
year = {1999},
month = {10},
volume = {39},
number = {19},
pages = {3267-3286},
abstract = {We determined two-dimensional motion discrimination contours in the spatio-temporal frequency plane to characterize the mechanisms underlying velocity perception. In particular, we wanted to determine whether there exist mechanisms tuned specifically to velocity, rather than separable mechanisms tuned to spatial and temporal frequency. A 4-AFC paradigm was used to determine spatio-temporal frequency discrimination thresholds for moving sinewave gratings defined by luminance contrast. Three of the grating patches used were defined by the same spatial and temporal frequency (standard), the other (test) differed by a fixed proportional change in spatial and temporal frequency. Subjects had to indicate which grating differed most from the others and the thresholds determined for varying proportions of change in spatial and temporal frequency were used to trace out complete threshold contours in the plane spanned by these attributes. Some of the contours, primarily at speeds above 1 deg/s, were noticeably oriented along lines of constant velocity. To further isolate these mechanisms, spatio-temporal noise was added to the standard stimuli either along a line of constant velocity or in the direction orthogonal to it. When spatio-temporal noise of constant velocity was added to the standard stimuli, threshold contours became elongated only along the direction of the noise. The same amount of noise in the orthogonal direction produced an overall increase in thresholds without changing the shape of the contour, presenting clear evidence for velocity tuned mechanisms. In further experiments we discovered that velocity tuned mechanisms interact with separable mechanisms to produce optimal discriminability. Analogous experiments with isoluminant stimuli failed to exhibit evidence for velocity tuning, supporting the notion that the human color vision system is impaired in its coding of stimulus speed, despite excellent sensitivity to direction of motion.},
url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/pdf211.pdf},
department = {Department B{\"u}lthoff},
web_url = {http://www.sciencedirect.com/science/article/pii/S0042698999000176},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
DOI = {10.1016/S0042-6989(99)00017-6},
author = {Reisbeck, TE and Gegenfurtner, KR}
}
@Article { 213,
title = {Contrast sensitivity and appearance in briefly presented illusory figures},
journal = {Spatial Vision},
year = {1999},
month = {7},
volume = {12},
number = {3},
pages = {329-344},
abstract = {We examined the contributions of brightness enhancement, illusory figure formation and figural completion to changes in contrast sensitivity in contour gaps. The brightness on the border of a Kanizsa-square and an outline square was measured as the point of subjective equality with the background (PSE) for small line targets. Increment and decrement thresholds were measured at the same location. We found that contrast thresholds were lower than in a control condition without inducers, and that the threshold reduction was independent of the contrast polarity of the inducers. This reduction cannot be explained by a simple summation of stimulus contrast and induced brightness. In a second experiment the inducers that define the contour of the Kanizsa and the outline square were changed so that the figure was no longer closed, keeping the local stimulus surround constant. Thresholds were equally reduced for all conditions, independently of whether the figure was completed or not, or whether an illusory contour was perceived or not. The results suggest that the reduction of contrast threshold in contour gaps is independent of the brightness perceived in these gaps and of the formation of an illusory figure. Processes that cause contrast threshold reduction in contour gaps also seem to operate independently of figural completion.},
department = {Department B{\"u}lthoff},
web_url = {http://www.ingentaconnect.com/content/vsp/spv/1999/00000012/00000003/art00005?token=005b1edb4cc8d54d6978b767232d45232b46243f38765731665d3e3f3568293c62207d673f582f6b092e5ce1dd5},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
DOI = {10.1163/156856899X00193},
author = {Rieger, JW and Gegenfurtner, KR}
}
@Article { 192,
title = {Seeing movement in the dark.},
journal = {Nature},
year = {1999},
month = {4},
volume = {398},
number = {6727},
pages = {475-476},
abstract = {Our visual world is greatly reduced at night. Spatial and temporal resolution are poor, contrast sensitivity is diminished, and colour vision is totally absent1, as rod photoreceptors are used rather than the cone photoreceptors that operate during the day. Many aspects of rod vision, including spectral, contrast and flicker sensitivity, have been studied in detail1, but motion perception has been largely ignored2. We find that motion perception using rods is impaired, with moving objects appearing to be slower than they are during cone vision.},
url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/pdf192.pdf},
department = {Department B{\"u}lthoff},
web_url = {http://www.nature.com/nature/journal/v398/n6727/pdf/398475a0.pdf},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
DOI = {10.1038/19004},
author = {Gegenfurtner, KR and Mayser, H and Sharpe, LT}
}
@Article { 215,
title = {Selective Color Constancy Deficits after Circumscribed Unilateral Brain Lesions},
journal = {Journal of Neuroscience},
year = {1999},
month = {4},
volume = {19},
number = {8},
pages = {3094-3106},
abstract = {The color of an object, when part of a complex scene, is determined not only by its spectral reflectance but also by the colors of all other objects in the scene (von Helmholtz, 1886; Ives, 1912; Land, 1959). By taking global color information into account, the visual system is able to maintain constancy of the color appearance of the object, despite large variations in the light incident on the retina arising from changes in the spectral content of the illuminating light (Hurlbert, 1998; Maloney, 1999). The neural basis of this color constancy is, however, poorly understood. Although there seems to be a prominent role for retinal, cone-specific adaptation mechanisms (von Kries, 1902; P{\"o}ppel, 1986; Foster and Nascimento, 1994), the contribution of cortical mechanisms to color constancy is still unclear (Land et al., 1983; D’Zmura and Lennie, 1986). We examined the color perception of 27 patients with defined unilateral lesions mainly located in the parieto-temporo-occipital and fronto-parieto-temporal cortex. With a battery of clinical and specially designed color vision tests we tried to detect and differentiate between possible deficits in central color processing. Our results show that color constancy can be selectively impaired after circumscribed unilateral lesions in parieto-temporal cortex of the left or right hemisphere. Five of 27 patients exhibited significant deficits in a color constancy task, but all of the 5 performed well in color discrimination or higher-level visual tasks, such as the association of colors with familiar objects. These results indicate that the computations underlying color constancy are mediated by specialized cortical circuitry, which is independent of the neural substrate for color discrimination and for assigning colors to objects.},
url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/pdf215.pdf},
department = {Department B{\"u}lthoff},
web_url = {http://www.jneurosci.org/content/19/8/3094.long},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
author = {R{\"u}ttiger, L and Braun, DI and Gegenfurtner, KR and Petersen, D and Sch{\"o}nle, P and Sharpe, LT}
}
@Article { 190,
title = {Neurobiology - The eyes have it!},
journal = {Nature},
year = {1999},
month = {3},
volume = {398},
number = {6725},
pages = {291-292},
abstract = {The transmission of visual signals from eye to brain involves considerable delays in conduction and processing1. Because stimuli of varying intensity or colour can cause different delays, it could be difficult to synchronize events from different parts of a visual scene — in particular, our perception of moving stimuli would consistently trail behind their real locations. But the visual system can circumvent such delays by anticipating the path of moving stimuli. Such motion anticipation was assumed to be controlled by high-level motion areas of the visual cortex. Now, very much to our surprise, Berry et al.2 (page 334 of this issue) report that motion anticipation is already accomplished to a large extent in the retina, by neural circuits that were discovered long ago.
Judging the location of moving objects is important for evading obstacles or predators and for catching prey. These tasks would be almost impossible if the relevant information was delayed. If, for example, we assume a processing delay1 of about 100 ms, an animal (or a car nowadays) moving at a speed of 40 km per hour would be seen more than one metre behind its actual position. To overcome this potentially lethal problem, evolution has selected mechanisms that anticipate the path of motion.
The existence of mechanisms that compensate for visual delays was uncovered by clever psychophysical experiments, which compared the perceived locations of flashed and moving objects3, 6 (Fig. 1). If presented at the same position, flashed objects are seen to trail moving objects by as much as 80 ms. The common interpretation of this phenomenon was that both types of stimuli — flashed and moving — go through the same delays in the eye, and that the position of the predictable, moving stimulus is then corrected by movement-selective mechanisms in areas of the brain concerned with analysing visual motion.},
url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/pdf190.pdf},
department = {Department B{\"u}lthoff},
web_url = {http://www.nature.com/nature/journal/v398/n6725/pdf/398291a0.pdf},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
DOI = {10.1038/18563},
author = {Gegenfurtner, KR}
}
@Article { 159,
title = {Visual psychophysics: synchrony in motion},
journal = {Nature Neuroscience},
year = {1998},
month = {6},
volume = {1},
number = {2},
pages = {96-98},
abstract = {Studies with ambiguous visual stimuli are claimed to indicate that synchronous neuronal oscillations can mediate perceptual binding. But the authors' interpretation will be controversial.},
url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/pdf159.pdf},
department = {Department B{\"u}lthoff},
web_url = {http://www.nature.com/neuro/journal/v1/n2/pdf/nn0698_96.pdf},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
DOI = {10.1038/344},
author = {Gegenfurtner, KR}
}
@Article { 252,
title = {Effects of contrast and temporal frequency on orientation discrimination for luminance and isoluminant stimuli},
journal = {Vision Research},
year = {1998},
month = {4},
volume = {38},
number = {8},
pages = {1105-1117},
abstract = {thresholds to stimulus contrast had similar shapes for luminance and isoluminant gratings, indicating similar processing mechanisms. Thresholds for stationary or slowly moving gratings were consistently lower for isoluminant than for luminance gratings, when contrast was expressed on an absolute RMS-cone-contrast scale. When contrast was defined as multiples of detection thresholds, discrimination was slightly better for luminance gratings. Thresholds for fast moving gratings were similar, irrespective of the definition of contrast. In contrast to previous work, we found a marked “oblique-effect” for both luminance and isoluminant gratings, when measuring discrimination thresholds as a function of standard orientation. Finally, we measured discrimination thresholds for gratings that varied in contrast and orientation simultaneously. The shapes of the resulting two-dimensional threshold contours were similar for luminance and isoluminant gratings, indicating again that these stimuli undergo similar neuronal processing. Performance of the observers could be described by probability summation of the orientation and contrast cues, resulting in an elliptical shape of the two-dimensional threshold contours. In conclusion, our results show similar performance for luminance and isoluminant gratings in several orientation discrimination tasks. The similarity in shape of the different threshold functions presents strong evidence that similar mechanisms underlie orientation discrimination of luminance and isoluminant stimuli.},
url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/pdf252.pdf},
department = {Department B{\"u}lthoff},
web_url = {http://www.sciencedirect.com/science/article/pii/S004269899700240X},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
DOI = {10.1016/S0042-6989(97)00240-X},
author = {Reisbeck, TE and Gegenfurtner, KR}
}
@Article { 230,
title = {The contribution of color to visual memory in X-chromosome-linked dichromats},
journal = {Vision Research},
year = {1998},
month = {4},
volume = {38},
number = {7},
pages = {1041-1045},
abstract = {We used a recognition memory paradigm to assess the visual memory of X-chromosome-linked dichromats for color images of natural scenes. The performance of 17 protanopes and 14 deuteranopes, who lack the second (red-green opponent) subsystem of color vision, but retain the primordial (yellow-blue opponent) subsystem, was compared with that of 36 color normal observers. During the presentation phase, 48 images of natural scenes were displayed on a CRT for durations between 50 and 1000 msec. Each image was followed by a random noise mask. Half of the images were presented in color and half in black and white. In the subsequent query phase, the same 48 images were intermixed with 48 new images and the subjects had to indicate which of the images they had already seen during the presentation phase. We find that the performance of the color normal observers increases with exposure duration. However, they perform 5–10\% better for colored than for black and white images, even at exposure durations as short as 50 msec. Surprisingly, performance is not impaired for the dichromats, whose recognition performance is also better for colored than for black and white images. We conclude either that X-chromosome-linked dichromats may be able to compensate for their reduced chromatic information range when viewing complex natural scenes or that the chromatic information in most natural scenes, for the durations tested, is sufficiently represented by the surviving primordial color subsystem.},
url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/pdf230.pdf},
department = {Department B{\"u}lthoff},
web_url = {http://www.sciencedirect.com/science/article/pii/S0042698997002009},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
DOI = {10.1016/S0042-6989(97)00200-9},
author = {Gegenfurtner, K and Wichmann, FA and Sharpe, LT}
}
@Article { 158,
title = {Thresholds for the identification of the direction of motion of plaid patterns defined by luminance or chromatic contrast},
journal = {Vision Research},
year = {1998},
month = {3},
volume = {38},
number = {6},
pages = {881-888},
abstract = {Contrast thresholds for identification of the direction of motion were determined for sinusoidal gratings and plaid patterns moving in eight possible directions. Since plaid patterns are the sum of two component gratings, a prediction of the thresholds for plaids can be made by assuming that the motions of both component gratings are independently identified (probability summation). In agreement with standard two-stage models of plaid perception, our results show that for stimuli defined by luminance contrast, plaid direction thresholds can be predicted well from the component thresholds. This also holds for fast-moving isoluminant plaid patterns, but for slowly moving (<4 Hz) isoluminant plaids, direction thresholds were substantially higher than the prediction from the components. In the latter case, subjects frequently were unable to identify the motion of the plaid in the pattern direction, even when the direction of motion of both components could be reliably identified. Different mechanisms might underlie the perception of luminance and isoluminant plaids at slow speeds.},
url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/pdf158.pdf},
department = {Department B{\"u}lthoff},
web_url = {http://www.sciencedirect.com/science/article/pii/S0042698997002149},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
DOI = {10.1016/S0042-6989(97)00214-9},
author = {Gegenfurtner, KR}
}
@Article { 366,
title = {Chromatic properties of neurons in macaque area V2},
journal = {Visual Neuroscience},
year = {1997},
month = {11},
volume = {14},
number = {5},
pages = {1061-1072},
abstract = {We recorded from single cells in area V2 of cynomolgus monkeys using standard acute recording techniques. After measuring each cell's spatial and temporal properties, we performed several tests of its chromatic properties using sine-wave gratings modulated around a mean gray background. Most cells behaved like neurons in area V1 and their responses were adequately described by a model that assumes a linear combination of cone signals. Unlike in V1, we found a subpopulation of cells whose activity was increased or inhibited by stimuli within a narrow range of color combinations. No particular color directions were preferentially represented. V2 cells showing color specificity, including cells showing narrow chromatic tuning, were present in any of the stripe compartments, as defined by cytochrome-oxidase (CO) staining. An addition of chromatic contrast facilitated the responses of most neurons to gratings with various luminance contrasts. Neurons in all three CO compartments gave significant responses to isoluminant gratings. Receptive-field properties of cells were generally similar for luminance and chromatically defined stimuli. We found only a small number of cells with a clearly identifiable double-opponent receptive-field organization.},
department = {Department B{\"u}lthoff},
web_url = {http://journals.cambridge.org/action/displayAbstract?fromPage=online\&aid=4650292},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
DOI = {10.1017/S0952523800011779},
author = {Kiper, DC and Fenstemaker, SB and Gegenfurtner, KR}
}
@Article { 360,
title = {Interpolation processes in the perception of real and illusory contours},
journal = {Perception},
year = {1997},
month = {11},
volume = {26},
number = {11},
pages = {1445-1458},
abstract = {The spatial and temporal characteristics of mechanisms that bridge gaps between line segments were determined. The presentation time that was necessary for localisation and identification of a triangular shape made up of pacmen, pacmen with lines, lines, line segments (corners), or pacmen with circles (amodal completion) was measured. The triangle was embedded in a field of distractors made up of the same components but at random orientations. Subjects had to indicate whether the triangle was on the left or on the right of the display (localisation) and whether it was pointing upward or downward (identification). Poststimulus masks consisted of pinwheels for the pacmen stimuli or wheels defined by lines. Stimuli were presented on a grey background and defined by luminance or isoluminant contrast. Thresholds were fastest when the triangle was defined by real contours, as for the pacmen with lines (105 ms) and the lines only (92 ms), slightly slower for corners (118 ms) and pacmen (136 ms), and much slower for the amodally completed pacmen (285 ms). For all inducer types localisation was about 20 ms faster than identification. In a second experiment the relative length of the gap between inducers was varied. Thresholds increased as a function of gap length, indicating that the gaps between the inducers need to be interpolated. There was no significant difference in the speed of this interpolation process between the pacman stimuli and the line-segment stimuli. About 40 mswere required to interpolate 1 deg of visual angle, corresponding to about one third of the distance between inducers. In a third experiment, it was found that processing of isoluminant stimuli was as fast as for low-contrast luminance stimuli, when targets were defined by real contours (lines), butmuch slower for illusory contours (pacmen). The conclusion is that the time necessary to interpolate a contour depends greatly on the spatial configuration of the stimulus. Since interpolation is faster for the line-segment stimuli, which do not elicit the percept of an illusory contour, the interpolation process seems to be independent of the formation of illusory contours.},
department = {Department B{\"u}lthoff},
web_url = {http://www.perceptionweb.com/abstract.cgi?id=p261445},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
DOI = {10.1068/p261445},
author = {Gegenfurtner, KR and Brown, JE and Rieger, JW}
}
@Article { 359,
title = {Visual neurobiology: Colouring the cortex},
journal = {Nature},
year = {1997},
month = {7},
volume = {388},
number = {6637},
pages = {23-24},
abstract = {In humans, the neural basis for colour vision lies in the activity of the 'colour-opponent' neurons, which receive inputs of opposite sign from the three different classes of cone photoreceptors that are found in the eye (Fig. 1). Colour-opponent neurons are abundant in the first stages of the visual pathway — the retina and the lateral geniculate nucleus. Surprisingly, however, they are observed rather infrequently by single-cell recordings in the next stage, the primary visual cortex (V1), where neurons that add inputs from all three cone types predominate.},
url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/pdf359.pdf},
department = {Department B{\"u}lthoff},
web_url = {http://www.nature.com/nature/journal/v388/n6637/full/388023a0.html},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
author = {Gegenfurtner, KR}
}
@Article { 361,
title = {Functional Properties of Neurons in Macaque Area V3},
journal = {Journal of Neurophysiology},
year = {1997},
month = {4},
volume = {77},
number = {4},
pages = {1906-1923},
abstract = {Functional properties of neurons in macaque area V3. J. Neurophysiol. 77: 1906–1923, 1997. We investigated the functional properties of neurons in extrastriate area V3. V3 receives inputs from both magno- and parvocellular pathways and has prominent projections to both the middle temporal area (area MT) and V4. It may therefore represent an important site for integration and transformation of visual signals. We recorded the activity of single units representing the central 10\(^{\circ}\) in anesthetized, paralyzed macaque monkeys. We measured each cell's spatial, temporal, chromatic, and motion properties with the use of a variety of stimuli. Results were compared with measurements made in V2 neurons at similar eccentricities. Similar to area V2, most of the neurons in our sample (80\%) were orientation selective, and the distribution of orientation bandwidths was similar to that found in V2. Neurons in V3 preferred lower spatial and higher temporal frequencies than V2 neurons. Contrast thresholds of V3 neurons were extremely low. Achromatic contrast sensitivity was much higher than in V2, and similar to that found in MT. About 40\% of all neurons showed strong directional selectivity. We did not find strongly directional cells in layer 4 of V3, the layer in which the bulk of V1 and V2 inputs terminate. This property seems to be developed within area V3. An analysis of the responses of directionally selective cells to plaid patterns showed that in area V3, as in MT and unlike in V1 and V2, there exist cells sensitive to the motion of the plaid pattern rather than to that of the components. The exact proportion of cells classified as being selective to color depended to a large degree on the experiment and on the criteria used for classification. With the use of the same conditions as in a previous study of V2 cells, we found as many (54\%) color-selective cells as in V2 (50\%). Furthermore, the responses of V3 cells to colored sinusoidal gratings were well described by a linear combination of cone inputs. The two subpopulations of cells responsive to color and to motion overlapped to a large extent, and we found a significant proportion of cells that gave reliable and directional responses to drifting isoluminant gratings. Our results show that there is a significant interaction between color and motion processing in area V3, and that V3 cells exhibit the more complex motion properties typically observed at later stages of visual processing.},
department = {Department B{\"u}lthoff},
web_url = {http://jn.physiology.org/content/77/4/1906.long},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
author = {Gegenfurtner, KR and Kiper, DC and Levitt, JB}
}
@Article { 449,
title = {Interaction of motion and color in the visual pathways},
journal = {Trends in Neurosciences},
year = {1996},
month = {9},
volume = {19},
number = {9},
pages = {394-401},
abstract = {In recent years the idea of parallel and independent processing streams for different visual attributes has become a guiding principle for linking the organization, architecture and function of the visual system. Findings concerning the segregation of motion and color information have been at the forefront of the evidence in favor of the parallel processing scheme. A number of studies have shown that motion perception is impaired for isoluminant stimuli, which are thought to isolate the color system. However, there are now many studies, the results of which are incompatible with the simple idea of segregated pathways. We propose two processing streams for motion that differ mostly in their temporal characteristics. Although neither of the two motion streams is color-blind, as was originally suggested, they differ radically in the way they process color information. The view that we propose provides a framework that reconciles a number of seemingly contradictory results. Evidence to support the new framework comes from psychophysical, physiological and lesion studies.},
department = {Department B{\"u}lthoff},
web_url = {http://download.cell.com/trends/neurosciences/pdf/PII0166223696100369.pdf},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
DOI = {10.1016/0166-2236(96)10036-9},
author = {Gegenfurtner, KR and Hawken, MJ}
}
@Article { 448,
title = {Perceived velocity of luminance, chromatic and non-fourier stimuli: Influence of contrast and temporal frequency},
journal = {Vision Research},
year = {1996},
month = {5},
volume = {36},
number = {9},
pages = {1281-1290},
abstract = {We measured perceived velocity as a function of contrast for luminance and isoluminant sinusoidal gratings, luminance and isoluminant plaids, and second-order, amplitude-modulated, drift-balanced stimuli. For all types of stimuli perceived velocity was contrast-invariant for fast moving patterns at or above 4 deg/sec. For slowly moving stimuli the log of perceived velocity was a linear function of the log of the contrast. The slope of this perceived velocity-vs-contrast line (velocity gain) was relatively shallow for luminance gratings and luminance plaids, but was steep for isoluminant gratings and isoluminant plaids, as well as for drift-balanced stimuli. Independent variation of spatial and temporal frequency showed that these variables, and not velocity alone, determine the velocity gain. Overall, the results indicate that slow moving stimuli defined by chromaticity or by second-order statistics are processed in a different manner from luminance defined stimuli. We propose that there are a number of independent mechanisms processing motion targets and it is the interplay of these mechanisms that is responsible for the final percept.},
department = {Department B{\"u}lthoff},
web_url = {http://www.sciencedirect.com/science/article/pii/0042698995001980},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
DOI = {10.1016/0042-6989(95)00198-0},
author = {Gegenfurtner, KR and Hawken, MJ}
}
@Article { 522,
title = {Cortical oscillatory responses do not affect visual segmentation},
journal = {Vision Research},
year = {1996},
month = {2},
volume = {36},
number = {4},
pages = {539-544},
abstract = {We tested the hypothesis that synchronization of oscillatory responses between populations of visually driven neurons could be the basis for visual segmentation and perceptual grouping. We reasoned that oscillations in response induced by flickering visual targets should have an effect on visual performance in these tasks. We therefore measured the psychophysical performance of human subjects in a texture segregation task (Expt I) and in a perceptual grouping task (Expt II). In both experiments, the elements composing the stimuli were flickered and presented in a variety of flicker conditions. These experimental conditions were designed to either interfere with naturally occuring synchronization of oscillations, or to induce synchronization and bias a subject's perceptual judgement. Performance in these tasks was neither helped nor hindered by the temporal pattern of flicker. These results suggest that physiologically observed oscillatory responses are unrelated to the processes underlying visual segmentation and perceptual grouping.},
url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/pdf522.pdf},
department = {Department B{\"u}lthoff},
web_url = {http://www.sciencedirect.com/science/article/pii/0042698995001352},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
DOI = {10.1016/0042-6989(95)00135-2},
author = {Kiper, DC and Gegenfurtner, KR and Movshon, JA}
}
@Article { 451,
title = {Processing of color, form, and motion in macaque area V2},
journal = {Visual Neuroscience},
year = {1996},
month = {1},
volume = {13},
number = {1},
pages = {161-172},
abstract = {We investigated the representation of color in cortical area V2 of macaque monkeys, and the association of color with other stimulus attributes. We measured the selectivity of individual V2 neurons for color, motion, and form. Most neurons in V2 were orientation selective, about half of them were selective for color, and a minority of cells (about 20\%) were selective for size or direction. We correlated these physiological measurements with the anatomical location of the cells with respect to the cytochrome oxidase (CO) compartments of area V2. There was a tendency for color-selective cells to be found more frequently in the thin stripes, but color-selective cells also occurred frequently in thick stripes and inter-stripes. We found no difference in the degree of color selectivity between the different CO compartments. Furthermore, there was no negative correlation between color selectivity and selectivity for other stimulus attributes. We found many cells capable of encoding information along more than one stimulus dimension, regardless of their location with respect to the CO compartments. We suggest that area V2 plays an important role in integrating information about color, motion, and form. By this integration of stimulus attributes a cue invariant representation of the visual world might be achieved.},
department = {Department B{\"u}lthoff},
web_url = {http://journals.cambridge.org/action/displayAbstract?fromPage=online\&aid=4616584\&fulltextType=RA\&fileId=S0952523800007203},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
DOI = {10.1017/S0952523800007203},
author = {Gegenfurtner, KR and Kiper, DC and Fenstemaker, SB}
}
@Article { 624,
title = {Temporal and chromatic properties of motion mechanisms},
journal = {Vision Research},
year = {1995},
month = {6},
volume = {35},
number = {11},
pages = {1547-1563},
abstract = {We measured threshold contours in color space for detecting drifting sinusoidal gratings over a range of temporal frequencies, and for identifying their direction of motion. Observers were able to correctly identify the direction of motion in all directions of color space, given a sufficiently high contrast. At low temporal frequencies we found differences between luminance and isoluminance conditions; for isoluminance there was a marked threshold elevation for identification when compared to detection. The threshold elevation for identification is dependent on eccentricity as well as on temporal frequency. At high temporal frequencies there were no differences between detection and identification thresholds, or between thresholds for luminance and isoluminance. A quantitative analysis of the threshold contours allowed us to identify two mechanisms contributing to motion: a color-opponent mechanism with a high sensitivity at low temporal frequencies and a luminance mechanism whose relative sensitivity increases with temporal frequency. An analysis of the cone contributions to motion detection and identification showed that L-cones dominated threshold behavior for both detection and identification at high temporal frequencies. There was a weak S-cone input to motion detection and identification at high temporal frequencies.},
department = {Department B{\"u}lthoff},
web_url = {http://www.sciencedirect.com/science/article/pii/004269899400264M},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
DOI = {10.1016/0042-6989(94)00264-M},
author = {Gegenfurtner, KR and Hawken, MJ}
}
@Inproceedings { 570,
title = {Repr{\"a}sentation und Verarbeitung sensorischer Information in biologischen und k{\"u}nstlichen Systemen},
year = {1996},
month = {9},
pages = {91},
department = {Department B{\"u}lthoff},
editor = {Thielscher , M. , S.-E. Bornscheuer},
publisher = {Dresden University Press},
address = {Dresden, Germany},
booktitle = {Fortschritte der k{\"u}nstlichen Intelligenz (KI 96)},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {Dresden, Germany},
event_name = {20. Deutsche Jahrestagung f{\"u}r K{\"u}nstliche Intelligenz},
author = {Gegenfurtner, KR and Schill, K}
}
@Techreport { 2004,
title = {The Dynamics of Visual Pattern Masking in Natural Scene
processing: A MEG-Study},
year = {2002},
month = {10},
number = {103},
abstract = {We investigated the mechanisms of pattern masking in a scene recognition task by recording simultaneously
psychophysical performance and magnetic brain activity using magnetoencephalography (MEG). Photographs
of natural scenes were displayed for various durations and then immediately followed by a pattern mask.
We were able to identify the transient brain activation caused by the switching from scene to mask. The latency
of this mask-transient signals the earliest cortical interaction between target and mask. The scenes alone elicited a transient occipital activation starting 70ms after stimulus onset, peaking at 110ms and reaching a minimum at 160ms. By comparing psychophysical performance with the latency of the mask transient and the dynamics of the undistorted processing of the scene at various SOAs we found that the initial occipital activation peak reflects processes vulnerable to pattern masking. The additional activation from the mask falling within this target-processing activity significantly reduces recognition performance. We found no measurable impact of mask activation later than 160ms after target onset. Our results indicate that the information necessary for the reliable recognition of a scene among a set of distracters can be extracted within about 90ms of cortical processing. Our data support the view, that the effect of the pattern backward mask occurs by overwriting a visual buffer in which the scene is stored during analysis.},
url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/pdf2004.pdf},
department = {Department B{\"u}lthoff},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
institution = {Max Planck Institute for Biological Cybernetics, T{\"u}bingen, Germany},
author = {Rieger, JW and Braun, C and Gegenfurtner, KR and B{\"u}lthoff, HH}
}
@Techreport { 1541,
title = {Motion Perception at Scotopic Light Levels},
year = {1999},
month = {12},
number = {76},
abstract = {Although the spatial and temporal properties of rod-mediated
vision have been extensively characterized, very little is known about
scotopic motion perception. To provide such information, we determined
thresholds for the detection and identification of the direction of
motion of sinusoidal grating patches moving at speeds from 1 to 32
deg/s, under scotopic light levels, in four different types of
observers: three normals, a rod monochromat (who lacks all cone
vision), an S-cone monochromat (who lacks M- and L-cone vision), and
four deuteranopes (who lack M-cone vision). The deuteranopes, whose
motion perception does not differ from that of normals, allowed us to
measure rod and L-cone thresholds under silent substitution conditions
and to directly compare the perceived velocity for moving stimuli
detected by either rod or cone vision at the same light level. We find,
for rod as for cone vision, that the direction of motion can be
reliably identified very near to detection threshold. In contrast, the
perceived velocity of rod-mediated stimuli is reduced by about 20\%
relative to cone-mediated stimuli at temporal frequencies below 4 Hz
and at all intensity levels investigated (0.92 to -1.12 log cd m-2).
Most likely the difference in velocity perception is distal in origin
because rod and cone signals converge in the retina and further
processing of their combined signals in the visual cortex is presumably
identical. To account for the difference, we propose a model of
velocity, in which the greater temporal averaging of rod signals in the
retina leads to an attenuation of the motion signal in the detectors
tuned to high velocities.},
url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/pdf1541.pdf},
department = {Department B{\"u}lthoff},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
institution = {Max Planck Institute for Biological Cybernetics T{\"u}bingen},
author = {Gegenfurtner, KR and Mayser, HM and Sharpe, LT}
}
@Techreport { 1346,
title = {The Effects of Visual Illusions on Grasping},
year = {1999},
month = {11},
number = {74},
abstract = {In recent years the view has been advocated that the motor system is immune to visual size illusions. This is regarded as a consequence of a fundamental division of labor in the primate brain: vision for action versus vision for
perception. We tested this claim for the Mueller-Lyer illusion and the Parallel-Lines illusion. Both illusions clearly affected grasping. The effects on grasping were similar though not perfectly equal to the effects on
perception. We present evidence that these small
differences are due to problems in matching the perceptual and the motor tasks. We argue that grasping is an inherently unipolar measure because only one object can be grasped with the same hand at a time, while perceptual measures usually are bipolar because they require a comparison of two objects. We show that this difference is a central problem in matching the perceptual and the motor
task.},
url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/effects_of_visual_illusions_on_grasping_1346[0]_1346[0].pdf},
department = {Department B{\"u}lthoff},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
institution = {Max Planck Institute for Biological Cybernetics, T{\"u}bingen, Germany},
author = {Franz, V and Fahle, M and B{\"u}lthoff, HH and Gegenfurtner, K}
}
@Techreport { 1537,
title = {Time course of chromatic adaptation for color appearance and discrimination},
year = {1999},
month = {10},
number = {69},
abstract = {Adaptation to a steady background has a profound effect on both color
appearance and discrimination. We determined the temporal
characteristics of chromatic adaptation for appearance and
discrimination along different color directions. Subjects were adapted
to a large uniform background made up of a CRT screen and a 45x64 deg
wall, illuminated by computer controlled lamps. After an instant
change in background color along a red-green or blue-yellow color
axes, we measured thresholds for the detection of increments along the
same axes at fixed times between 25 ms and 121 s. Analogously, color
appearance was determined using achromatic matching. Three components
of adaptation could be identified by their temporal characteristics. A
slow exponential time course of adaptation with a half-life of about
20 seconds was common to appearance and discrimination. A faster
component with a half-life of 40-70 ms - probably due to photoreceptor
adaptation - was also common to both. Exclusive for color appearance,
there was a third, extremely rapid mechanism with a half-life faster
than 10ms. This instantaneous process explained more than 50\% of total
adaptation for color appearance and could be shown to act in a
multiplicative manner. We conclude that this instantaneous adaptation
mechanism for color appearance is situated at a later processing
stage, after mechanisms common to appearance and discrimination, and
is based on multiplicative spatial interactions rather than on local,
temporal adaptational processes. Color appearance, and thus color
constancy, seems to be determined in large part by cortical
computations.},
url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/pdf1537.pdf},
department = {Department B{\"u}lthoff},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
institution = {Max Planck Institute for Biological Cybernetics T{\"u}bingen},
author = {Rinner, O and Gegenfurtner, KR}
}
@Techreport { 1535,
title = {Grasping visual illusions: No evidence for a dissociation
between perception and action},
year = {1999},
month = {2},
number = {67},
abstract = {Neuropsychological studies motivated the theory that the
primate visual system might be organized into two parallel pathways, one for conscious perception and one to guide action (Milner \& Goodale, 1995). Supporting evidence in healthy humans seemed to come from a dissociation in visual illusions: Aglioti, DeSouza, and Goodale (1995) reported that the Ebbinghaus (or Titchener) Illusion deceived
perceptual judgments of size, but only marginally influenced the size estimates used in grasping. Here we show that identical effects of the illusion are found if the perceptual and grasping tasks are appropriately matched. We show that the differences found by Aglioti
et al. (1995) can be accounted for by a hitherto unknown, super additive effect in the illusion. We conclude that the illusion does not provide evidence for the existence of two distinct pathways for perception and action in the visual system.},
department = {Department B{\"u}lthoff},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
institution = {Max Planck Institute for Biological Cybernetics, T{\"u}bingen, Germany},
author = {Franz, V and Gegenfurtner, K and B{\"u}lthoff, HH and Fahle, M}
}
@Techreport { 1526,
title = {Velocity Tuned Mechanisms in Human Motion Processing},
year = {1998},
number = {58},
url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/pdf1526.pdf},
department = {Department B{\"u}lthoff},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
institution = {Max Planck Institute for Biological Cybernetics T{\"u}bingen},
author = {Reisbeck, TE and Gegenfurtner, KR}
}
@Techreport { 1498,
title = {Chromatic Properties of Neurons in Macaque Area V2},
year = {1996},
month = {7},
number = {34},
abstract = {We recorded from single cells in area V2 of cynomolgus monkeys using
standard acute recording techniques. After measuring each cell's
spatial and temporal properties, we performed several tests of its
chromatic properties using sinewave gratings modulated around a mean
gray background. Most cells behaved like neurons in area V1 and their
response was adequately described by a model that assumes a linear
combination of cone signals. Unlike in V1, we found a subpopulation of
cells whose activity was increased or inhibited by stimuli within a
narrow range of color combinations. No particular color directions
were preferentially represented. V2 cells showing color-specificity,
including cells showing narrow chromatic tuning, could be found in any
of the stripe compartments, as defined by cytochrome-oxidase (CO)
staining. An addition of chromatic contrast facilitated the responses
of most neurons to gratings with various luminance contrasts. Neurons
in all three CO-compartments gave a significant population response to
isoluminant gratings. Receptive fields properties of cells were
generally similar for luminance and chromatically defined stimuli. We
found only a small number of cells with a clearly identifiable
double-opponent receptive field organization. The similarity between
the chromatic tuning characteristics of individual color-specific
cells in area V2 and psychophysically observed higher order color
mechanisms suggests an important role for area V2 in the cortical
hierarchy for the processing of color signals.},
note = {This technical report has also been published elsewhere},
department = {Department B{\"u}lthoff},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
institution = {Max Planck Institute for Biological Cybernetics, T{\"u}bingen, Germany},
author = {Kiper, DC and Fenstemaker, SB and Gegenfurtner, KR}
}
@Techreport { 1495,
title = {Effects of Contrast, Temporal Frequency and Chromatic
Content on Orientation Discrimination},
year = {1996},
month = {6},
number = {32},
abstract = {We compared the mechanisms responsible for orientation discrimination
of stimuli defined by luminance and red/green isoluminant contrast in
three tasks. A 4-AFC paradigm was used to determine thresholds for
discriminating 1 cpd sinewave gratings differing in orientation,
contrast, or both. When measuring orientation thresholds as a function
of stimulus contrast, we found a decrease in thresholds with
increasing stimulus contrast. For three temporal frequencies (0 Hz, 1
Hz, and 8 Hz) the functions relating orientation thresholds to
stimulus contrast had similar shapes for luminance and isoluminant
gratings, indicating similar processing mechanisms. Thresholds for
stationary and slowly moving gratings were consistently lower for
isoluminant than for luminance gratings when contrast was expressed on
an absolute RMS-cone-contrast scale. When contrast was defined as
multiples of detection thresholds discrimination was slightly better
for luminance gratings. Thresholds for fast moving gratings were
similar irrespective of the definition of contrast. For both luminance
and isoluminant gratings, we found a marked ''oblique-effect'' when
measuring thresholds as a function of standard orientation. Finally,
we measured discrimination thresholds for gratings that varied in
contrast and orientation simultaneously. The shapes of the resulting
two-dimensional threshold contours were similar for luminance and
isoluminant gratings, indicating again that these stimuli undergo the
same neuronal processing. Performance of the observers could be
described by probability summation of the orientation and contrast
cues, resulting in an elliptical shape of the two-dimensional
threshold contours. In conclusion, our results show similar
performance for luminance and isoluminant gratings in three different
orientation discrimination tasks. The similarity in shape of the
different threshold functions presents strong evidence that a single
common mechanism might underlie orientation discrimination of
luminance and isoluminant stimuli.},
note = {This technical report has also been published elsewhere},
department = {Department B{\"u}lthoff},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
institution = {Max Planck Institute for Biological Cybernetics, T{\"u}bingen, Germany},
author = {Reisbeck, TE and Gegenfurtner, KR}
}
@Techreport { 1492,
title = {Functional Properties of Neurons in Macaque Area V3},
year = {1996},
month = {4},
number = {29},
note = {This technical report has also been published elsewhere},
department = {Department B{\"u}lthoff},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
institution = {Max Planck Institute for Biological Cybernetics, T{\"u}bingen, Germany},
author = {Gegenfurtner, KR and Kiper, DC and Levitt, JB}
}
@Techreport { 1491,
title = {Integration Processes in the Perception of Real and Illusory Contours},
year = {1996},
month = {3},
number = {28},
abstract = {We measured spatial and temporal characteristics of mechanisms that
bridge gaps between line segments. The presentation time was measured
which was necessary for localization and identification of a triangular
shape made up of (a) pacmen, (b) pacmen with lines, (c) lines, (d) line
segments (corners) or (e) pacmen with circles (amodal completion). The
triangle was embedded in a field of distractors of the same components
at random orientations. Subjects had to indicate whether the triangle
was to the left or to the right of the midline (localization) and
whether it was pointing upward or downward (identification).
Poststimulus masks consisted of pinwheels (a, b, e) or randomly
oriented lines (c, d). Stimuli were presented on a gray background and
defined by luminance or isoluminant contrast. Thresholds were fastest
when the triangle was defined by real contours (b: 98 msec; c: 106
msec), slightly slower for corners and pacmen (d:129 msec; a: 157
msec), and much slower for the amodally completed pacmen (e: 355 msec).
For all pattern types localization was about 20 msec faster than
identification. Compared to low contrast luminance stimuli, processing
of isoluminant stimuli was equally fast for targets defined by real
contours (c), but much slower for illusory contours (a). We conclude
that speed of contour integration depends greatly on the spatial
configuration of the stimulus, but not directly on the formation of
illusory contours. The contour integration process is impaired under
conditions of isoluminance, but not the perception of contours per se.},
department = {Department B{\"u}lthoff},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
institution = {Max Planck Institute for Biological Cybernetics, T{\"u}bingen, Germany},
author = {Gegenfurtner, KR and Brown, JE and Rieger, JW}
}
@Techreport { 1143,
title = {The contribution of colour to recognition memory in normal and colour-deficient observers},
year = {1996},
month = {2},
number = {25},
abstract = {We used a recognition memory paradigm to assess the influence of color
information on visual memory for color images of natural scenes.
During the presentation phase 48 images of natural scenes were
presented on a CRT for exposure durations between 50 and 1000 msec
followed by a random noise mask. Half of the images were presented in
color and half in black \& white. In the subsequent query phase the
same 48 images were intermixed with 48 new images and the subjects had
to indicate which of the images they had already seen during the
presentation phase. We found that performance increased with exposure
duration. However, independent of exposure duration subjects performed
5-10\% better for colored than for black \& white images, even for
exposure durations as short as 50 msec. This effect cannot be due to
contrast differences in the images since a second experiment showed
little effect of contrast once the images were suprathreshold. Further
experiments showed that performance worsened when images were
presented in color and tested in black \& white, or vice versa.
Performance was not impaired for a comparison group of 31 color
deficient observers (17 protanopes and 14 deuteranopes), whose
recognition performance was also better for colored than for black \&
white images. We conclude that color information plays an important
role in the early and fast processing of visual images. Both sensory
and cognitive factors seem to contribute to the superior recognition
of color images. Finally, color-deficient observers appear to be able
to compensate for their reduced chromatic information range when
viewing and analyzing complex scenes.},
url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/pdf1143.pdf},
department = {Department B{\"u}lthoff},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
institution = {Max Planck Institute for Biological Cybernetics, T{\"u}bingen, Germany},
author = {Gegenfurtner, KR and Wichmann, FA and Sharpe, LT}
}
@Techreport { 1469,
title = {Integration of Color Information in Macaque Area V2},
year = {1995},
month = {1},
number = {10},
abstract = {We investigated the representation of color in cortical area V2 of macaque monkeys, and the association of color with other stimulus attributes. We measured the selectivity of individual V2 neurons for color, motion and form. Most neurons in V2 were orientation selective, about half of them were selective for color, and a minority of cells
(about 20\%) were selective for size or direction. We correlated these physiological measurements with the anatomical location of the cells with respect to the cytochrome oxidase (CO) compartments of area V2. There was a tendency for color selective cells to be more frequent in
the thin stripes, but color selective cells did also occur frequently in thick stripes and inter-stripes. We found no difference in the degree of color selectivity between the different CO-compartments. Furthermore, there was no negative correlation between color selectivity and selectivity for other stimulus attributes. We found
many cells capable of encoding information along more than one stimulus dimension, regardless of their location with respect to the CO-compartments. We suggest that area V2 plays an important role in integrating information about color, motion and form. By this integration of stimulus attributes a cue-invariant representation of the visual world might be achieved.},
note = {This technical report has also been published elsewhere},
department = {Department B{\"u}lthoff},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
institution = {Max Planck Institute for Biological Cybernetics T{\"u}bingen},
author = {Gegenfurtner, KR and Kiper, DC and Fenstemaker, SB}
}
@Techreport { 1470,
title = {Perceived speed of luminance, chromatic and non-Fourier stimuli: influence of contrast and temporal frequency},
year = {1995},
month = {1},
number = {11},
abstract = {We measured perceived speed as a function of contrast for luminance and isoluminant sinusoidal gratings, luminance and isoluminant plaids, and second order amplitude- modulated drift-balanced stimuli. For all types of stimuli perceived speed was contrast- invariant for fast moving patterns at or above 4 Hz. For slowly moving stimuli the log of perceived speed was a linear function of the log of the contrast. The slope of this speed- versus-contrast line (velocity gain) was relatively shallow for luminance gratings and luminance plaids, but was steep for isoluminant gratings and isoluminant plaids, as well as
for the drift-balanced stimuli. Independent variation of spatial and temporal frequency showed that these variables, and not velocity, determine the velocity gain. Over all the results indicate that slow moving stimuli defined by chromaticity or by second-order statistics are processed in different manner from luminance defined stimuli. We propose that there are a number of independent mechanisms processing
motion targets and it is the interplay of these mechanisms that is responsible for the final percept.},
note = {This technical report has also been published elsewhere},
department = {Department B{\"u}lthoff},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
institution = {Max Planck Institute for Biological Cybernetics T{\"u}bingen},
author = {Gegenfurtner, KR and Hawken, MJ}
}
@Poster { 4383,
title = {Classification of natural scenes: Critical features revisited},
journal = {Journal of Vision},
year = {2006},
month = {6},
volume = {6},
number = {6},
pages = {561},
abstract = {Human observers are capable of detecting animals within novel natural scenes with remarkable speed and accuracy. Despite the seeming complexity of such decisions it has been hypothesized that a simple global image feature, the relative abundance of high spatial frequencies at certain orientations, could underly such fast image classification (A. Torralba \& A. Oliva, Network: Comput. Neural Syst., 2003).
We successfully used linear discriminant analysis to classify a set of 11.000 images into “animal” and “non-animal” images based on their individual amplitude spectra only (Drewes, Wichmann, Gegenfurtner VSS 2005). We proceeded to sort the images based on the performance of our classifier, retaining only the best and worst classified 400 images (“best animals”, “best distractors” and “worst animals”, “worst distractors”).
We used a Go/No-go paradigm to evaluate human performance on this subset of our images. Both reaction time and proportion of correctly classified images showed a significant effect of classification difficulty. Images more easily classified by our algorithm were also classified faster and better by humans, as predicted by the Torralba \& Oliva hypothesis.
We then equated the amplitude spectra of the 400 images, which, by design, reduced algorithmic performance to chance whereas human performance was only slightly reduced (cf. Wichmann, Rosas, Gegenfurtner, VSS 2005). Most importantly, the same images as before were still classified better and faster, suggesting that even in the original condition features other than specifics of the amplitude spectrum made particular images easy to classify, clearly at odds with the Torralba \& Oliva hypothesis.},
department = {Department Sch{\"o}lkopf},
web_url = {http://journalofvision.org/6/6/561/},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {Sarasota, FL, USA},
event_name = {6th Annual Meeting of the Vision Sciences Society (VSS 2006)},
language = {en},
DOI = {10.1167/6.6.561},
author = {Drewes, J and Wichmann, FA and Gegenfurtner, K}
}
@Poster { 4834,
title = {Classification of Natural Scenes: Critical Features Revisited},
year = {2006},
month = {3},
volume = {9},
pages = {92},
abstract = {Human observers are capable of detecting animals within novel natural scenes with remarkable speed and accuracy. Despite the seeming complexity of such decisions it has been hypothesized that a simple global image feature, the relative abundance of high spatial frequencies at certain orientations, could underly such fast image classification [1].
We successfully used linear discriminant analysis to classify a set of 11.000 images into animal and non-animal images based on their individual amplitude spectra only [2]. We proceeded to sort the images based on the performance of our classifier, retaining only the best and worst classified 400 images (''best animals'', ''best distractors'' and ''worst animals'', ''worst distractors'').
We used a Go/No-go paradigm to evaluate human performance on this subset of our images. Both reaction time and proportion of correctly classified images showed a significant effect of classification difficulty. Images more easily classified by our algorithm were also classified faster and better by humans, as predicted by the Torralba \& Oliva hypothesis.
We then equated the amplitude spectra of the 400 images, which, by design, reduced algorithmic performance to chance whereas human performance was only slightly reduced [3]. Most importantly, the same images as before were still classified better and faster, suggesting that even in the original condition features other than specifics of the amplitude spectrum made particular images easy to classify, clearly at odds with the Torralba \& Oliva hypothesis.},
department = {Department Sch{\"o}lkopf},
web_url = {http://www.twk.tuebingen.mpg.de/twk06/abstract.php?_load_id=drewes01},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {T{\"u}bingen, Germany},
event_name = {9th T{\"u}bingen Perception Conference (TWK 2006)},
language = {en},
author = {Drewes, J and Wichmann, FA and Gegenfurtner, KR}
}
@Poster { 4387,
title = {Classification of natural scenes: critical features revisited},
journal = {Experimentelle Psychologie},
year = {2006},
month = {3},
volume = {48},
pages = {251},
department = {Department Sch{\"o}lkopf},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {Mainz, Germany},
event_name = {48. Tagung Experimentell Arbeitender Psychologen (TeaP 2006)},
language = {en},
author = {Drewes, J and Wichmann, FA and Gegenfurtner, K}
}
@Poster { 4469,
title = {Classification of natural scenes using global image statistics},
journal = {Journal of Vision},
year = {2005},
month = {9},
volume = {5},
number = {8},
pages = {602},
abstract = {The algorithmic classification of complex, natural scenes is generally considered a difficult task due to the large amount of information conveyed by natural images. Work by Simon Thorpe and colleagues showed that humans are capable of detecting animals within novel natural scenes with remarkable speed and accuracy. This suggests that the relevant information for classification can be extracted at comparatively limited computational cost. One hypothesis is that global image statistics such as the amplitude spectrum could underly fast image classification (Johnson \& Olshausen, Journal of Vision, 2003; Torralba \& Oliva, Network: Comput. Neural Syst., 2003).
We used linear discriminant analysis to classify a set of 11.000 images into animal and non-animal images. After applying a DFT to the image, we put the Fourier spectrum into bins (8 orientations with 6 frequency bands each). Using all bins, classification performance on the Fourier spectrum reached 70\%. However, performance was similar (67\%) when only the high spatial frequency information was used and decreased steadily at lower spatial frequencies, reaching a minimum (50\%) for the low spatial frequency information. Similar results were obtained when all bins were used on spatially filtered images. A detailed analysis of the classification weights showed that a relatively high level of performance (67\%) could also be obtained when only 2 bins were used, namely the vertical and horizontal orientation at the highest spatial frequency band.
Our results show that in the absence of sophisticated machine learning techniques, animal detection in natural scenes is limited to rather modest levels of performance, far below those of human observers. If limiting oneself to global image statistics such as the DFT then mostly information at the highest spatial frequencies is useful for the task. This is analogous to the results obtained with human observers on filtered images (Kirchner et al, VSS 2004).},
department = {Department Sch{\"o}lkopf},
web_url = {http://www.journalofvision.org/5/8/602/},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {Sarasota, FL, USA},
event_name = {Fifth Annual Meeting of the Vision Sciences Society (VSS 2005)},
language = {en},
DOI = {10.1167/5.8.602},
author = {Drewes, J and Wichmann, FA and Gegenfurtner, KR}
}
@Poster { 3049,
title = {Fixating for grasping},
journal = {Journal of Vision},
year = {2005},
month = {9},
volume = {5},
number = {8},
pages = {117},
abstract = {In a grasping task, Johansson et al. (2001) found that subjects look at the position to which the finger tips are guided. However, in their experiment, only the contact position of the thumb was visible. We investigated what happens if the contact positions of both finger and thumb are visible. We recorded eye and finger movements. In a first experiment, subjects always grasped with the index finger at the top and the thumb at the bottom of a flat shape that was mounted on a horizontal bar. In order to see whether a salient feature of a shape would affect the fixation positions, we presented an (asymmetric) cross in 4 orientations (with the crossing of the bars representing the salient feature). In order to see whether gaze is attracted to the position where the finger has to be guided relatively precisely, we presented a triangle in two orientations that subjects had to contact at the base and at the pointed top (i.e., a higher required precision to contact the top than the base). We found that the crossing of the bars cross attracted the gaze whereas the top of a triangle did not. A prominent result was that subjects fixated above the center of the shape. In order to distinguish between subjects fixating the upper part of the shape versus being attracted by the index finger, we mounted a square and a triangle in two orientations on a vertical bar. We asked subjects to grasp first with one hand and then with the other so that the shape remained constant but the contact positions of the index finger and thumb were reversed. Subjects still looked above the center. In addition, the gaze was attracted to the index finger for the triangle but to the thumb for the square. We conclude that both features of the shape and the grasp affect gaze location. The exact location depends on the specific circumstances.},
department = {Department B{\"u}lthoff},
web_url = {http://www.journalofvision.org/content/5/8/117},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {Sarasota, FL, USA},
event_name = {Fifth Annual Meeting of the Vision Sciences Society (VSS 2005)},
DOI = {10.1167/5.8.117},
author = {Brouwer, A-M and Franz, VH and Kerzel, D and Gegenfurtner, KR}
}
@Poster { 3555,
title = {Rapid animal detection in natural scenes: Critical features are local},
journal = {Journal of Vision},
year = {2005},
month = {9},
volume = {5},
number = {8},
pages = {376},
abstract = {Thorpe et al (Nature 381, 1996) first showed how rapidly human observers are able to classify natural images as to whether they contain an animal or not. Whilst the basic result has been replicated using different response paradigms (yes-no versus forced-choice), modalities (eye movements versus button presses) as well as while measuring neurophysiological correlates (ERPs), it is still unclear which image features support this rapid categorisation. Recently Torralba and Oliva (Network: Computation in Neural Systems, 14, 2003) suggested that simple global image statistics can be used to predict seemingly complex decisions about the absence and/or presence of objects in natural scences. They show that the information contained in a small number (N=16) of spectral principal components (SPC)—principal component analysis (PCA) applied to the normalised power spectra of the images—is sufficient to achieve approximately 80\% correct animal detection in natural scenes.
Our goal was to test whether human observers make use of the power spectrum when rapidly classifying natural scenes. We measured our subjects' ability to detect animals in natural scenes as a function of presentation time (13 to 167 msec); images were immediately followed by a noise mask. In one condition we used the original images, in the other images whose power spectra were equalised (each power spectrum was set to the mean power spectrum over our ensemble of 1476 images). Thresholds for 75\% correct animal detection were in the region of 20–30 msec for all observers, independent of the power spectrum of the images: this result makes it very unlikely that human observers make use of the global power spectrum. Taken together with the results of Gegenfurtner, Braun \& Wichmann (Journal of Vision [abstract], 2003), showing the robustness of animal detection to global phase noise, we conclude that humans use local features, like edges and contours, in rapid animal detection.},
department = {Department Sch{\"o}lkopf},
web_url = {http://www.journalofvision.org/5/8/376/},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {Sarasota, FL, USA},
event_name = {Fifth Annual Meeting of the Vision Sciences Society (VSS 2005)},
language = {en},
DOI = {10.1167/5.8.376},
author = {Wichmann, FA and Rosas, P and Gegenfurtner, K}
}
@Poster { 3558,
title = {Classification of natural scenes using global image statistics},
journal = {Experimentelle Psychologie},
year = {2005},
month = {4},
volume = {47},
pages = {88},
department = {Department Sch{\"o}lkopf},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {Regensburg, Germany},
event_name = {47. Tagung Experimentell Arbeitender Psychologen (TeaP 2005)},
author = {Drewes, J and Wichmann, FA and Gegenfurtner, K}
}
@Poster { 3554,
title = {Rapid animal detection in natural scenes: critical features are local},
journal = {Experimentelle Psychologie},
year = {2005},
month = {4},
volume = {47},
pages = {225},
department = {Department Sch{\"o}lkopf},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {Regensburg, Germany},
event_name = {47. Tagung Experimentell Arbeitender Psychologen (TeaP 2005)},
author = {Wichmann, F and Rosas, P and Gegenfurtner, K}
}
@Poster { DrewesWG2005,
title = {Classification of Natural Scenes using Global Image Statistics},
year = {2005},
month = {2},
volume = {8},
pages = {88},
abstract = {The algorithmic classification of complex, natural scenes is generally considered a difficult
task due to the large amount of information conveyed by natural images. Work by Simon
Thorpe and colleagues showed that humans are capable of detecting animals within novel natural
scenes with remarkable speed and accuracy. This suggests that the relevant information
for classification can be extracted at comparatively limited computational cost. One hypothesis
is that global image statistics such as the amplitude spectrum could underly fast image classification
(Johnson \& Olshausen, Journal of Vision, 2003; Torralba \& Oliva, Network: Comput.
Neural Syst., 2003).
We used linear discriminant analysis to classify a set of 11.000 images into animal and nonanimal
images. After applying a DFT to the image, we put the Fourier spectrum of each image
into 48 bins (8 orientations with 6 frequency bands). Using all of these bins, classification
performance on the Fourier spectrum reached 70\%. In an iterative procedure, we then removed
the bins whose absence caused the smallest damage to the classification performance (one
bin per iteration). Notably, performance stayed at about 70\% until less then 6 bins were left.
A detailed analysis of the classification weights showed that a comparatively high level of
performance (67\%) could also be obtained when only 2 bins were used, namely the vertical
orientations at the highest spatial frequency band. When using only a single frequency band
(8 bins) we found that 67\% classification performance could be reached when only the high
spatial frequency information was used, which decreased steadily at lower spatial frequencies,
reaching a minimum (50\%) for the low spatial frequency information. Similar results were
obtained when all bins were used on spatially pre-filtered images.
Our results show that in the absence of sophisticated machine learning techniques, animal
detection in natural scenes is limited to rather modest levels of performance, far below those
of human observers. If limiting oneself to global image statistics such as the DFT then mostly
information at the highest spatial frequencies is useful for the task. This is analogous to the
results obtained with human observers on filtered images (Kirchner et al, VSS 2004).},
department = {Department Sch{\"o}lkopf},
department2 = {Department B{\"u}lthoff},
web_url = {http://www.twk.tuebingen.mpg.de/twk05/programm.php},
event_place = {T{\"u}bingen, Germany},
event_name = {8th T{\"u}bingen Perception Conference (TWK 2005)},
author = {Drewes, J and Wichmann, FA and Gegenfurtner, KR}
}
@Poster { BrouwerFKG2005,
title = {Looking During Grasping},
year = {2005},
month = {2},
volume = {8},
pages = {161},
abstract = {In a grasping task, Johansson et al. [1] found that subjects look at the position to which the
finger tips are guided. However, in their experiment, only the contact position of the thumb
was visible. We investigated what happens if the contact positions of both finger and thumb are
visible. We recorded eye and finger movements. In a first experiment, subjects always grasped
with the index finger at the top and the thumb at the bottom of a flat shape that was mounted on
a horizontal bar. In order to see whether a salient feature of a shape would affect the fixation
positions, we presented an (asymmetric) cross in 4 orientations (with the crossing of the bars
representing the salient feature). In order to see whether gaze is attracted to the position where
the finger has to be guided relatively precisely, we presented a triangle in two orientations that
subjects had to contact at the base and at the pointed top (i.e., a higher required precision to
contact the top than the base). We found that the crossing of the bars attracted the gaze whereas
the top of a triangle did not. A prominent result was that subjects fixated above the center of
the shape. In order to distinguish between subjects fixating the upper part of the shape versus
being attracted by the index finger, we mounted a square and a triangle in two orientations on a
vertical bar. We asked subjects to grasp first with one hand and then with the other so that the
shape remained constant but the contact positions of the index finger and thumb were reversed.
Subjects still looked above the center. In addition, for the square the gaze was now attracted to
the thumb so that the average fixation location was to the left or to the right half of the square,
depending on the used hand. The latter result indicates that gaze not only depends on the shape
but also on features of the grasp. This is also supported by the finding that the variability in
fixation locations was more in the horizontal direction for the second experiment than for the
first, i.e. the variability tends to be along the grasping axis. We conclude that both features of
the shape and the grasp affect gaze location.},
department = {Department B{\"u}lthoff},
web_url = {http://www.twk.tuebingen.mpg.de/twk05/programm.php},
event_place = {T{\"u}bingen, Germany},
event_name = {8th T{\"u}bingen Perception Conference (TWK 2005)},
author = {Brouwer, A-M and Franz, V and Kerzel, D and Gegenfurtner, KR}
}
@Poster { 3560,
title = {Global image statistics of natural scenes},
journal = {Bioinspired Information Processing},
year = {2005},
volume = {08},
pages = {1},
department = {Department Sch{\"o}lkopf},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
author = {Drewes, J and Wichmann, F and Gegenfurtner, K}
}
@Poster { 2634,
title = {Greifen isoluminanter Stimuli},
journal = {Experimentelle Psychologie},
year = {2004},
month = {4},
volume = {46},
pages = {258},
abstract = {Visuelle Information wird in anatomisch unterschiedlichen kortikalen Pfaden verarbeitet, deren genaue Funktion jedoch noch umstritten ist. Goodale und Milner [TiNS,15,97-112(1992)] ordnen dem ventralen Pfad Aufgaben der Objekterkennung zu, w{\"a}hrend der dorsale Pfad visuelle Reize zur Ausf{\"u}hrung von motorischen Handlungen verarbeiten soll. Auch die Verarbeitung von Farbinformation wird h{\"a}ufig dem ventralen Pfad zugeordnet. Man k{\"o}nnte also annehmen, dass das Greifen von Objekten, die ausschlie{\ss}lich {\"u}ber ihre Farbe definiert sind, beeintr{\"a}chtigt ist. Wir untersuchten Greifbewegungen nach im Vergleich zum Hintergrund isoluminanten (gr{\"u}n, X=0.2856, Y=0.6020) vs. {\"u}ber
ihren Helligkeitskontrast definierte Scheiben verschiedener Gr{\"o}{\ss}e (30, 35 und 40 mm). Diese wurden visuell {\"u}ber einen Spiegel dargestellt, haptisch verwendeten wir reale Scheiben unter dem Spiegel. In einer Wahrnehmungsaufgabe stellten die Versuchsteilnehmer die Gr{\"o}{\ss}e eines Vergleichsreizes ein. Wir fanden keine Beeintr{\"a}chtigung der Greifbewegung oder Gr{\"o}{\ss}enwahrnehmung im isoluminanten Fall. Reine Farbinformation kann zur Ausf{\"u}hrung der Greifbewegung genutzt werden.},
url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/pdf2634.pdf},
department = {Department B{\"u}lthoff},
web_url = {http://www.allpsych.uni-giessen.de/teap/index.php},
editor = {Kerzel, D., V. Franz and K. Gegenfurtner},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {Giessen, Germany},
event_name = {46. Tagung Experimentell Arbeitender Psychologen (TeaP 2004)},
author = {Stockmeier, K and Gegenfurtner, KR and B{\"u}lthoff, HH and Franz, VH}
}
@Poster { 2377,
title = {The importance of phase information for recognizing natural images},
journal = {Journal of Vision},
year = {2003},
month = {10},
volume = {3},
number = {9},
pages = {519},
abstract = {Fourier phase plays an important role in determining image structure. For example, when the phase spectrum of an image showing a flower is swapped with the phase spectrum of an image showing a tank, then we will usually perceive a tank in the resulting image, even though the amplitude spectrum is still that of the flower. Also, when the phases of an image are randomly swapped across frequencies, the resulting image becomes impossible to recognize. Our goal was to evaluate the effect of phase manipulations in a more quantitative manner. On each trial subjects viewed two images of natural scenes. The subject had to indicate which one of the two images contained an animal. The spectra of the images were manipulated by adding random phase noise at each frequency. The phase noise was uniformly distributed in the interval [-phi,phi], where phi was varied between 0 degree and 180 degrees. Image pairs were displayed for 100 msec. Subjects were remarkably resistant to the addition of phase noise. Even with [−120,120] degree noise, subjects still were at a level of 75\% correct. The introduction of phase noise leads to a reduction of image contrast. Subjects were slightly better than a simple prediction based on this contrast reduction. However, when contrast response functions were measured in the same experimental paradigm, we found that performance in the phase noise experiment was significantly lower than that predicted by the corresponding contrast reduction.},
department = {Department B{\"u}lthoff},
department2 = {Department Sch{\"o}lkopf},
web_url = {http://www.journalofvision.org/content/3/9/519.abstract},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {Sarasota, FL, USA},
event_name = {Third Annual Meeting of the Vision Sciences Society (VSS 2003)},
author = {Gegenfurtner, KR and Braun, DI and Wichmann, FA}
}
@Poster { 2131,
title = {Phase Information and the Recognition of Natural Images},
year = {2003},
month = {2},
volume = {6},
pages = {138},
abstract = {Fourier phase plays an important role in determining image structure. For example,
when the phase spectrum of an image showing a
ower is swapped with the phase
spectrum of an image showing a tank, then we will usually perceive a tank in the
resulting image, even though the amplitude spectrum is still that of the
ower. Also,
when the phases of an image are randomly swapped across frequencies, the resulting
image becomes impossible to recognize. Our goal was to evaluate the e ect of phase
manipulations in a more quantitative manner. On each trial subjects viewed two images
of natural scenes. The subject had to indicate which one of the two images contained
an animal. The spectra of the images were manipulated by adding random phase noise
at each frequency. The phase noise was uniformly distributed in the interval [ ;+ ],
where was varied between 0 degree and 180 degrees. Image pairs were displayed for
100 msec. Subjects were remarkably resistant to the addition of phase noise. Even with
[120; 120] degree noise, subjects still were at a level of 75\% correct. The introduction
of phase noise leads to a reduction of image contrast. Subjects were slightly better
than a simple prediction based on this contrast reduction. However, when contrast
response functions were measured in the same experimental paradigm, we found that
performance in the phase noise experiment was signi cantly lower than that predicted
by the corresponding contrast reduction.},
department = {Department Sch{\"o}lkopf},
web_url = {http://www.twk.tuebingen.mpg.de/twk03/},
editor = {H.H. B{\"u}lthoff, K.R. Gegenfurtner, H.A. Mallot, R. Ulrich, F.A. Wichmann},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {T{\"u}bingen, Germany},
event_name = {6. T{\"u}binger Wahrnehmungskonferenz (TWK 2003)},
author = {Braun, DI and Wichmann, FA and Gegenfurtner, KR}
}
@Poster { 1154,
title = {Phase information in the recognition of natural images},
journal = {Perception},
year = {2002},
month = {8},
volume = {31},
number = {ECVP Abstract Supplement},
pages = {133},
abstract = {Fourier phase plays an important role in determining global image structure. For example, when the phase spectrum of an image of a flower is swapped with that of a tank, we usually perceive a tank, even though the amplitude spectrum is still that of the flower. Similarly, when the phase spectrum of an image is randomly swapped across frequencies, that is its Fourier energy is randomly distributed over the image, the resulting image becomes impossible to recognise. Our goal was to evaluate the effect of phase manipulations in a quantitative manner. Subjects viewed two images of natural scenes, one of which contained an animal (the target) embedded in the background. The spectra of the images were manipulated by adding random phase noise at each frequency. The phase noise was the independent variable, uniformly distributed between 0\(^{\circ}\) and ±180\(^{\circ}\). Subjects were remarkably resistant to phase noise. Even with ±120\(^{\circ}\) noise, subjects were still 75\% correct. The proportion of correct answers closely followed the correlation between original and noise-distorted images. Thus it appears as if it was not the global phase information per se that determines our percept of natural images, but rather the effect of phase on local image features.},
department = {Department Sch{\"o}lkopf},
web_url = {http://www.perceptionweb.com/abstract.cgi?id=v020075},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {Glasgow, UK},
event_name = {25th European Conference on Visual Perception},
author = {Braun, DI and Wichmann, FA and Gegenfurtner, KR}
}
@Poster { 62,
title = {A comparison of localization and pointing accuracy in peripheral position judgements},
journal = {Investigative Ophthalmology \& Visual Science},
year = {2001},
month = {5},
volume = {42},
number = {4},
pages = {S651},
department = {Department B{\"u}lthoff},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {Fort Lauderdale, FL, USA},
event_name = {Annual Meeting of the Association for Research in Vision and Ophthalmology (ARVO 2001)},
author = {Gegenfurtner, KR and Franz, VH}
}
@Poster { 1340,
title = {Ein Vergleich von Wahrnehmung und Handlung bei der peripheren Lokalisation},
journal = {Experimentelle Psychologie},
year = {2001},
month = {4},
volume = {43},
abstract = {Ziel dieser Experimente war ein Vergleich der
Genauigkeit mit der die Position von peripher
dargebotenen Objekten eingeschaetzt wird mit der
Genauigkeit von Zeigebewegungen zu diesen Objekten
hin. Die Vpn mussten dabei in jedem Durchgang die
Position eines scheibenfoermigen Reizes relativ zu
einer konstanten Markierungslinie
angeben. Gleichzeitig mussten die Vpn mit dem
Zeigefinger auf die Scheibe zeigen. Die
Zeigebewegungen wurden mit einem Optotrak-System
aufgezeichnet. Dabei war die perzeptuelle
Genauigkeit deutlich hoeher als die Genauigkeit
der Zeigebewegungen (9 versus 14 Winkelminuten)
Fuer die einzelnen Versuchspersonen (N=11) ergab
sich jedoch eine hohe Korrelation (rho=0.72)
zwischen den beiden Aufgaben. Des weiteren
korrelierten die Lokalisationsfehler bei beiden
Aufgaben fuer alle Vpn ueber die einzelnen
Durchgaenge hinweg. Die Ergebnisse unterstuetzen
die Hypothese dass die Signale, die die
wahrgenommene Position eines Objekts bestimmen
auch benutzt werden um das motorische System bei
Zeigebewegungen zu fuehren.},
department = {Department B{\"u}lthoff},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {Regensburg, Germany},
event_name = {43. Tagung Experimentell Arbeitender Psychologen (TeaP 2001)},
author = {Gegenfurtner, KR and Franz, VH}
}
@Poster { 60,
title = {Cone contrast sensitivity in human trichromats and dichromats},
year = {2001},
month = {3},
pages = {71},
abstract = {Our goal was to compare the long-wavelength (L-), middle-wavelength (M-) and short-wavelength (S-) cone contrast sensitivities of normal trichromats with those of deuteranopes (who lack M-cone function) and protanopes (who lack L-cone function).
8 trichromats and 8 dichromats (4 deuteranopes and 4 protanopes) served as observers. In a 4-AFC staircase procedure, their contrast thresholds were measured for detecting the position of a 1 or 16 Hz-flickering, 4\(^{\circ}\) dia. target. The target was presented on a neutral grey background, which was bright enough (10.2 cd/m2 or 2.1 log scotopic tds) to desensitize the rods. A silent substitution technique was used to selectively modulate the target color contrast so that it stimulated only the L-, M- or S-cones.
At 1 Hz, trichromats had significantly better L- and M-cone contrast sensitivities than deuteranopes and protanopes, respectively. But the S-cone contrast sensitivities of all three groups were similar. At 16 Hz, the L-cone contrast sensitivities of trichromats did not differ from those of deuteranopes, but their M-cone contrast sensitivities were significantly poorer than those of protanopes. Once again, the S-cone contrast sensitivities of all three groups were similar.
These results are consistent with cone photoreceptor replacement occurring in the dichromat eye and influencing the sensitivity of the post-receptoral chromatic and luminance channels. The 1 Hz targets were selected to favour the chromatic channels, which are functionally altered in the dichromats; hence presumably the better performance of the normal trichromats. On the other hand, the 16 Hz targets were selected to favor the luminance channel, the sensitivity of which is predominantly an additive combination of the L- and M-cone inputs. Given a typical L-/M-cone ratio (1.5) in the normal eye and the full substitution of the missing by the remaining cone type in dichromats, then replacing L- by M-cones in protanopes (200\% increase) may bring more benefit in contrast sensitivity than replacing M- by L-cones (50\% increase) in deuteranopes.},
department = {Department B{\"u}lthoff},
web_url = {http://www.twk.tuebingen.mpg.de/twk01/Pkontrast.htm},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {T{\"u}bingen, Germany},
event_name = {4. T{\"u}binger Wahrnehmungskonferenz (TWK 2001)},
author = {De Luca, E and Sharpe, LT and Gegenfurtner, KR}
}
@Poster { 119,
title = {A comparison of pursuit eye movement and perceptual performance in speed discrimination},
journal = {Perception},
year = {2000},
month = {8},
volume = {29},
number = {ECVP Abstract Supplement},
pages = {37},
abstract = {A central goal of sensation and perception is to direct our interactions with the environment. During most voluntary motor actions that are driven by sensory input we consciously experience an internal representation of the visual world. This leads to the question how faithful this internal representation is, and how precise our actions are compared to this reference. To answer that question, we studied the relationship between the perceived speed, which is the experiential representation of the stimulus, and the speed of smooth-pursuit eye movements, the motor action.
We determined psychophysical thresholds for detecting small perturbations in the speed of Gabor patterns (1 cycle deg-1) moving at a base speed of 4 deg s-1. At the same time we recorded eye-movement traces and used an ideal-observer analysis to compute analogous 'oculometric' thresholds. Our results show a remarkable agreement between perceptual judgments for speed discrimination and the fine gradations in eye-movement speed, with psychophysical and oculometric functions exhibiting the same slope. However, there was no correlation between perceptual errors and eye-movement errors on a trial-by-trial basis. We conclude that the motor system and perception share the same constraints in their analysis of motion signals, but they act independently and have different sources of noise.},
url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/pdf119.pdf},
department = {Department B{\"u}lthoff},
web_url = {http://www.perceptionweb.com/abstract.cgi?id=v000115},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {Groningen, Netherlands},
event_name = {23rd European Conference on Visual Perception (ECVP 2000)},
author = {Gegenfurtner, KR and Hawken, MJ and Scott, BH}
}
@Poster { 116,
title = {Effects of visual illusions on grasping: The parallel-lines illusion},
journal = {Investigative Ophthalmology \& Visual Science},
year = {2000},
month = {5},
volume = {41},
number = {4},
pages = {S43},
url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/pdf116.pdf},
department = {Department B{\"u}lthoff},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {Fort Lauderdale, FL, USA},
event_name = {Annual Meeting of the Association for Research in Vision and Ophthalmology (ARVO 2000)},
author = {Franz, VH and Fahle, M and Gegenfurtner, KR and B{\"u}lthoff, HH}
}
@Poster { 134,
title = {Predicting the recognition of natural scenes from single trial MEG recordings},
journal = {Investigative Ophthalmology \& Visual Science},
year = {2000},
month = {5},
volume = {41},
number = {4},
pages = {S962},
url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/pdf134.pdf},
department = {Department B{\"u}lthoff},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {Fort Lauderdale, FL, USA},
event_name = {Annual Meeting of the Association for Research in Vision and Ophthalmology (ARVO 2000)},
author = {Rieger, JW and Plum, F and Gegenfurtner, KR and Braun, C and Preissl, H and B{\"u}lthoff, HH}
}
@Poster { 1343,
title = {Gr{\"o}{\ss}enillusionen beeinflussen das Greifen - wie auch die Wahrnehmung},
journal = {Experimentelle Psychologie},
year = {2000},
month = {4},
volume = {42},
pages = {36},
abstract = {In den letzten Jahren ueberprueften wir den
Befund, dass visuelle Grosssenillusionen auf die
Greifmotorik einen deutlich geringeren Einfluss
ausueben als auf die Wahrnehmung (Aglioti, DeSouza\& Goodale, 1995). Dies wurde bisher als Indiz
dafuer gewertet, dass Informationen ueber visuelle
Grossse vom Wahrnehmungs- und vom Handlungssystem
unabhaengig ausgewertet werden (Action
vs. Perception-Hypothese, Milner \& Goodale,
1995). Es sollen unsere Ergebnisse zur Ebbinghaus
Illusion, zur Mueller-Lyer Illusion und zur
Parallele-Linien Illusion zusammenfassend
dargestellt werden. Die Hauptergebnisse sind: (a)
Greifen wird von optischen Illusionen
beeinflusst. (b) Der Einfluss auf das Greifen
stimmt nicht immer exakt mit dem Einfluss auf die
Wahrnehmung ueberein. Diese Unterschiede liessen
sich jedoch bisher mit unterschiedlichen
Anforderungen von Wahrnehmungsaufgabe und
Greifaufgabe erklaeren. Aufgrund dieser Ergebnisse
kommen wir zu dem Schluss, dass Greifen bei
optischen Taueschungen keine Evidenz fuer eine
Dissoziation zwischen Wahrnehmungs- und
Handlungssystem bietet.},
department = {Department B{\"u}lthoff},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {Braunschweig, Germany},
event_name = {42. Tagung Experimentell Arbeitender Psychologen (TeaP 2000)},
author = {Franz, VH and Gegenfurtner, KR and B{\"u}lthoff, HH and Fahle, M}
}
@Poster { 130,
title = {A color indexing system based on perception (CISBOP)},
year = {2000},
month = {2},
pages = {45},
abstract = {Color is an important feature for searching large databases of images, since it is invariant
with respect to camera position, object orientation and size, and partial occlusion. There
are currently many color-based image indexing systems (e.g. Flickner et al., 1995), which
all basically work by building color histograms in RGB space. Our goal was to construct
a color-indexing system based on the known properties of the human color vision system.
Our images were chosen from a large commercially available (COREL) image database
consisting of 60.000 digitized photographs. For each image, we buildt a color histogram
by converting the RGB triplets for each pixel into color-opponent coordinates. These luminance,
red-green, and yellow-blue coordinates correspond to the color directions found
in human color vision (Krauskopf, Williams \& Heeley, 1982). Luminance was averaged
for each color value, and the resulting color circle was split into 127 segments. The categories
were constructed so that the number of hue categories increased with increasing
saturation. Six different rings were used for saturation, with the radius doubling as saturation
increases. Thus, there is little discrimination of hues for unsaturated colors, whereas
there are 64 different hues at the most saturated level. Two different histograms were
built, one using the frequencies with which the different colors occurred, and another one
that used the average luminance level of each color segment.
We used a query-by-example stragey for searching. Several different distance measures
were evaluated by asking human observers to make similarity judgments. For most images,
this search, based on color only, results in images that are perceptually and often semantically
similar to the target image.},
url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/pdf130.pdf},
department = {Department B{\"u}lthoff},
web_url = {http://www.twk.tuebingen.mpg.de/twk00/},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {T{\"u}bingen, Germany},
event_name = {3. T{\"u}binger Wahrnehmungskonferenz (TWK 2000)},
author = {Neumann, D and Gegenfurtner, KR}
}
@Poster { 136,
title = {Beitrag der Zapfen zur Farbkonstanz},
year = {2000},
month = {2},
pages = {49},
abstract = {Farbkonstanz ist die wahrgenommene Konstanz der Farberscheinung unter variierenden
Beleuchtungsbedingungen. {\"A}nderungen der Lichtquelle werden kompensiert; die
Objektfarben {\"a}ndern sich scheinbar kaum. Verschiedene Mechanismen werden als
Grundlage dieses Ph{\"a}nomens diskutiert. Nach dem Zapfenskalierungsmodell wird die
Zapfenerregung bei Beleuchtungs{\"a}nderung durch lokale Adaptation normalisiert und
dadurch konstant gehalten. Im Model von Foster und Nascimento ist die r{\"a}umliche Korrelation
der Zapfenerregung unter Beleuchtungswechsel das Konstanzsignal: Bei einer
Beleuchtungs{\"a}nderung bleibt die Rangfolge der Zapfenerregung der einzelnen Objekte
erhalten.
Durch Messung der zeitlichen Entwicklung von Farbkonstanz unter Bedingungen mit
r{\"a}umlich korrelierten versus dekorrelierten {\"A}nderungen der Reizchromatizit{\"a}ten untersuchten
wir den Beitrag von Zapfenmechanismen zur Farbkonstanz bei schnellen
Beleuchtungswechseln.
Die Versuchspersonen adaptierten auf einen Hintergrund, der aus einem Monitor und
einer 45x64 Grad gro{\ss}en homogenen Wand aufgebaut war, die mit computergesteuerten
Leuchtstofflampen beleuchtet wurde. Auf dem Monitor wurden 400 Farbchips dargestellt,
deren Chromatizit{\"a}t entsprechend der Hintergrundbeleuchtung simuliert wurde.
Nach vollst{\"a}ndiger Adaptation wechselte die Hintergrundbeleuchtung und die Chromatizit{\"a}t
der Farbchips entlang der kardinalen rot-gr{\"u}n (L-M) Achse. 25 ms und 250 ms nach
Wechsel der Adaptationsbedingung wurde ein Testreiz dargeboten. Durch Grauwerteinstellung
konnte die Farbkonstanz zu diesen Zeitpunkten bestimmt werden.
Der Wechsel der Beleuchtungsbedingungen erfolgte korreliert oder unkorreliert. In der
korrelierten Bedingung wurde die Chromatizit{\"a}t jedes Farbchips entsprechend der neuen
Beleuchtung simuliert. In der unkorrelierten Bedingung {\"a}nderte sich zwar die mittlere
Chromatizit{\"a}t der Farbchips, doch die Farben wurden zuf{\"a}llig den Chips zugeordnet.
Wir fanden einen schnellen Mechanismus, der nach 25ms Adaptation auf die neue
Beleuchtungsbedingung {\"u}ber 50\% der Farbkonstanz erkl{\"a}rt, die nach vollst{\"a}ndiger
Adaptation erreicht wird. Dieser Zeitverlauf ist schneller als alle bekannten adaptiven
Prozesse des Zapfensystems. Die Korrelation der Zapfenerregung unter Beleuchtungs{\"a}nderungen
hatte keinen Einflu{\ss} auf diesen schnellen Mechanismus der Farbkonstanz.
Wir schlie{\ss}en aus diesen Ergebnissen, da{\ss} ein gro{\ss}er Anteil der Farbkonstanz nicht
durch lokale Zapfenprozesse sondern durch globalere Eigenschaften von beleuchteten
Szenen erkl{\"a}rt werden mu{\ss}.},
department = {Department B{\"u}lthoff},
web_url = {http://www.twk.tuebingen.mpg.de/twk00/},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {T{\"u}bingen, Germany},
event_name = {3. T{\"u}binger Wahrnehmungskonferenz (TWK 2000)},
author = {Rinner, O and Gegenfurtner, KR}
}
@Poster { 117,
title = {Der Einflu{\ss} optischer T{\"a}uschungen auf das Greifen: Die Parallele-Linien T{\"a}uschung},
year = {2000},
month = {2},
pages = {154},
abstract = {Motorische Handlungen sollen von optischen T{\"a}uschungen kaum beeinflu{\ss}t werden.
Dies wird als Indiz daf{\"u}r gewertet, dass visuelle Information durch qualitativ unterschiedliche
Prozesse f{\"u}r die Zwecke von Wahrnehmung und Handlung verarbeitet wird
(z.B. Aglioti, DeSouza, \& Goodale, 1995, Current Biology 5, 679-685). Im Gegensatz zu
dieser Auffassung konnten wir zeigen, dass Greifen von der Ebbinghaus / Titchener Illusion
in {\"a}hnlicher Weise wie die Wahrnehmung beeinflu{\ss}t wird (Franz, Gegenfurtner,
B{\"u}lthoff, \& Fahle, 2000; Psychological Science 11, 20-25). In der vorliegenden Studie
sollten diese Experimente auf die Parallele-Linien Illusion verallgemeinert werden.
Sechsundzwanzig Versuchspersonen wurden Plastik-St{\"a}bchen (40, 43, 46 und 49 mm
lang, 5 mm breit) pr{\"a}sentiert. Parallel zu den St{\"a}bchen wurden in einem Abstand von 11
mm zwei Linien pr{\"a}sentiert, die entweder 100 mm (illusion{\"a}r vergr{\"o}{\ss}ernde Figur) oder
22 mm lang waren (illusion{\"a}r verkleinernde Figur). Bei der Greifaufgabe sollten die Versuchspersonen
die St{\"a}bchen greifen und die maximale Hand{\"o}ffnung zwischen Zeigefinger
und Daumen wurde mittels eines Optotrak (TM) Systems gemessen. Bei der Wahrnehmungsaufgabe
stellten die Versuchspersonen einen Vergleichsreiz auf einem
Computermonitor so ein, dass er ihnen gleich lang erschien wie das Plastik-St{\"a}bchen.
Die Ergebnisse zeigen klare Effekte der Parallele-Linien Illusion sowohl auf das Greifen
wie auch auf dieWahrnehmung. Der Greifeffekt (1,2 +/- 0,32 mm) war jedoch kleiner als
der Wahrnehmungseffekt (2,3 +/- 0,26 mm). Die individuelle Gr{\"o}{\ss}e der Effekte korrelierte
zwischen den Versuchspersonen (r = 0,61; p<0,001). Das hei{\ss}t, eine Versuchsperson,
die einen starken Wahrnehmungseffekt hatte, zeigte ebenfalls einen gro{\ss}en Effekt
auf das Greifen.
Die Parallele Linien Illusion ist die erste Illusion, bei der wir einen konsistent kleineren
Illusionseffekt auf das Greifen als auf die Wahrnehmung gefunden haben. Wir fanden
jedoch ebenfalls eine starke Korrelation der Effekte zwischen den Versuchspersonen.
Dies legt nahe, dass der Greifeffekt und der Wahrnehmungseffekt den gleichen Ursprung
haben. Gr{\"u}nde f{\"u}r die absolut kleinere Gr{\"o}{\ss}e des Greifeffekts werden diskutiert.},
url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/pdf117.pdf},
department = {Department B{\"u}lthoff},
web_url = {http://www.twk.tuebingen.mpg.de/twk00/},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {T{\"u}bingen, Germany},
event_name = {3. T{\"u}binger Wahrnehmungskonferenz (TWK 2000)},
author = {Franz, VH and Fahle, M and Gegenfurtner, KR and B{\"u}lthoff, HH}
}
@Poster { 118,
title = {Retinale und kortikale Beitr{\"a}ge zu Farbadaptation und Farbkonstanz},
year = {2000},
month = {2},
pages = {42},
abstract = {Unter Farbkonstanz versteht man die F{\"a}higkeit des visuellen Systems, die Farbe von
Objekten als relativ konstant unter sich ver{\"a}ndernden Beleuchtungsbedingungen wahrzunehmen.
Obwohl es verschiedenen Modelle gibt, die theoretisch relativ gute Farbkonstanzleistungen
erzielen k{\"o}nnen, ist bisher immer noch unklar, ob Farbkonstanz bereits in
retinalen Schaltkreisen erreicht wird, oder ob dazu kortikale Mechanismen n{\"o}tig sind.
Wenn farbige Reize von gro{\ss}en farbigen Fl{\"a}chen umgeben werden, dann haben diese
Umfeldreize enormen Einflu{\ss} nicht nur auf die Farberscheinung, sondern auch auf die
Unterscheidbarkeit. In Experimenten mit schnellen Umfeld{\"a}nderungen konnten wir drei
Prozesse mit underschiedlichen Zeitkonstanten identifizieren. Ein langsamer Prozess mit
einer Halbwertszeit von ca. 30 s und ein schnellerer Prozess mit einer Halbwertszeit von
50-100 ms traten sowohl bei Farberscheinung und Farbunterscheidung auf. Der schnellste
Prozess jedoch, der ca. 70\% der gesamten Farb{\"a}nderung bei Beleuchtungswechseln
erkl{\"a}rte und eine Halbwertszeit von weniger als 20 ms hatte, trat nur bei der Farberscheinung
auf. Daher muss dieser Prozess, der wohl auf globale Reiz-Umfeld-kontraste
zur{\"u}ckgeht, auf einer sp{\"a}teren Verarbeitungsebene stattfinden als die langsameren. Mit
anderen Worten, die Bestimmung der Farberscheinung findet erst nach der Farbunterscheidung
statt. Der Einflu{\ss} von Beleuchtungs{\"a}nderungen wird also auf einer kortikalen
Ebene korrigiert.
Diese Ergebnisse stehen im Einklang mit Untersuchungen an Patienten mit kortikalen
Hirnl{\"a}sionen (R{\"u}ttiger et al., 1999). In dieser Studie fanden wir Patienten, die ein selektives
Defizit f{\"u}r Farbkonstanz bei unbeeintr{\"a}chtigter Farbunterscheidung aufwiesen. Drei
dieser Patienten hatten L{\"a}sionen in einem Bereich des Temporalkortex, der bisher nicht
mit Farbwahrnehmung in Verbindung gebracht wurde.
Diese Ergebnisse belegen, da{\ss} Farbkonstanzleistungen in erster Linie von spezialisierten
kortikalen Mechanismen erbracht werden, und da{\ss} diese Mechanismen unabh{\"a}ngig von
anderen Farbwahrnehmungsleistungen sind.},
department = {Department B{\"u}lthoff},
web_url = {http://www.twk.tuebingen.mpg.de/twk00/},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {T{\"u}bingen, Germany},
event_name = {3. T{\"u}binger Wahrnehmungskonferenz (TWK 2000)},
author = {Gegenfurtner, KR}
}
@Poster { 135,
title = {Single trial MEG recordings can predict the subject's ability to recognize a natural scene},
year = {2000},
month = {2},
pages = {97},
abstract = {To test the predictive power of brain activity during encoding of a natural scene for subsequent
recognition.
Evoked magnetic fields (EMF) were recorded while subjects performed a delayed matchto-
sample task with briefly presented and masked natural images. On each trial a digitized
image was presented for 37ms on a projection screen and immediately followed by
a pattern mask (1 sec). In the subsequent query phase, the subjects first had to judge
whether they would be able to recognize the image. Then the target and three distractor
images were shown, and the subjects had to indicate the target image (4AFC). During the
first 600 ms of presentation EMF’s were recorded with a CTF 151 channels whole cortex
system. We then used the MEG activity from individual trials to predict the subject’s
behavioural response on that trial. To circumvent the effects of guessing, we used only
those trials in which the subjects confidence judgement and recognition performance
agreed. We tested two classifiers, the partial correlation (PC) of a trial with the mean vectors
of correct and false trials and Support Vector (SV) classification which seeks a separating
hyperplane by maximizing the distance to the nearest samples of each class.
In 76.7\% of the trials the subjects confidence judgement and response agreed. In 78\% of
these trials the subjects gave a correct response. With PC on average 75.3\% of the correct
and 76.3\% of the false trials were correctly classified. But for only one subject best classification
was obtained with PC. Classification by support vector machines were typically
about 10-15\% better than with the PC classifier. Average performance with the best support
vector classifier was about 90.7\% for the correct and about 92.8\% for the false trials.
It is possible, with about 90\% accuracy, to predict in single trials subjects’ subsequent
recognition performance from the early information in the evoked magnetic fields
recorded while subjects were viewing the stimulus.},
url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/pdf135.pdf},
department = {Department B{\"u}lthoff},
web_url = {http://www.twk.tuebingen.mpg.de/twk00/},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {T{\"u}bingen, Germany},
event_name = {3. T{\"u}binger Wahrnehmungskonferenz (TWK 2000)},
author = {Rieger, JW and Plum, F and Gegenfurtner, KR and Braun, C and Preissl, H and B{\"u}lthoff, HH}
}
@Poster { 322,
title = {Categorisation of complex natural images in extreme peripheral vision},
journal = {Perception},
year = {1999},
month = {8},
volume = {28},
number = {ECVP Abstract Supplement},
pages = {61},
abstract = {Humans are very good at detecting animals in briefly flashed photographs of natural scenes, both in central [Thorpe et al, 1996 Nature (London) 381 520 - 522)] and in parafoveal vision [Fabre-Thorpe et al, 1998, in Computational Neuroscience: Trends in Research Eds J Bower (New York: Plenum Press) pp 7 - 12]. To test how far this ability extends into the periphery, we tested, ten human subjects in a 180 deg panoramic viewing theatre. 1400 highly varied photographs (37.5 deg high by 25 deg wide) were flashed for 28 ms, and subjects were asked to release a button if the image included an animal. Image position varied randomly from trial to trial with nine possible positions covering the entire horizontal extent of the visual field. Performance was remarkably good and decreased linearly with eccentricity from 93.3\% for central presentations, to 60.4\% for images centred at 75 deg, a remarkable result given the very low ganglion cell densities so far in the periphery. Note that this level of performance was only possible if the subjects were made to guess--most subjects were totally unaware of what had been presented in the far periphery. The results imply that rapid, automatic, and largely unconscious processing may be far more sophisticated that has been thought in the past.},
department = {Department B{\"u}lthoff},
web_url = {http://www.perceptionweb.com/abstract.cgi?id=v990238},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {Trieste, Italy},
event_name = {22nd European Conference on Visual Perception},
author = {Thorpe, S and Gegenfurtner, KR and Fabre-Thorpe, M and B{\"u}lthoff, HH}
}
@Poster { 312,
title = {Physiological basis of backward masking in scene recognition},
journal = {Perception},
year = {1999},
month = {8},
volume = {28},
number = {ECVP Abstract Supplement},
pages = {9},
abstract = {We examined the physiological basis of backward masking by recording evoked magnetic fields with a whole-head MEG-system during a recognition task. On each trial, a digitised image of a natural scene was displayed, immediately followed by a noise mask. Subsequently, the target and a distractor were shown, and subjects had to indicate the target. At 92 ms and 37 ms of presentation time, recognition performance was 97\% and 67\% correct, respectively. The MEG data revealed that, in the first 80 - 120 ms, activity was concentrated over the occipital cortex. At the 92 ms target duration, the mask had no effect on the initial activity caused by the target. However, at 37 ms of target duration, processing of the mask briefly interfered with the target. A significant difference in MEG activation in correct and false trials occurred at about 160 ms after target onset. The results indicate that, during the first 40 ms of processing of a natural scene, new information arriving in the early visual areas can lead to a profound degradation of recognition performance, correlating with the temporal overlap of target and mask signals in occipital cortex. Later processing stages, beyond 180 ms, seem to be unaffected by the mask.},
department = {Department B{\"u}lthoff},
web_url = {http://www.perceptionweb.com/abstract.cgi?id=v990208},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {Trieste, Italy},
event_name = {22nd European Conference on Visual Perception},
author = {Rieger, JW and Gegenfurtner, KR and Braun, C and Preissl, H and B{\"u}lthoff, HH}
}
@Poster { 313,
title = {Time course of adaptation for colour appearance and discrimination},
journal = {Perception},
year = {1999},
month = {8},
volume = {28},
number = {ECVP Abstract Supplement},
pages = {32},
abstract = {Adaptation to a steady background has a profound effect on both colour appearance and discriminability. We determined the temporal characteristics of adaptation for appearance and discrimination, and for changes along different colour directions. Subjects were adapted to a large uniform background made up of a CRT screen and a 60 deg \(\times\) 60 deg wall illuminated by computer-controlled lamps. After an instant change in background colour along the red - green or blue - yellow cardinal colour axes, we measured thresholds for the detection of increments or decrements along the same axes at fixed times between 16 and 120 s. Analogously, colour appearance was determined by means of observer production of achromatic appearance. We found a slow exponential time-course of adaptation with a half-life of 20 - 30 s that was common to appearance and discrimination. Also, a 50 - 100 ms component could be identified, which was probably due to photoreceptor adaptation. There was an extremely fast mechanism with a half-life faster than 10 ms, but only for colour appearance. There were no differences for adaptational changes along the different colour axes. We conclude that the fast adaptation mechanism for colour appearance is of higher order and is situated after the mechanisms mediating slower adaptational changes in colour discrimination and appearance.},
department = {Department B{\"u}lthoff},
web_url = {http://www.perceptionweb.com/abstract.cgi?id=v990209},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {Trieste, Italy},
event_name = {22nd European Conference on Visual Perception},
author = {Rinner, O and Gegenfurtner, KR}
}
@Poster { 310,
title = {Backwards masking in visual scene recognition: A MEG study},
journal = {Investigative Ophthalmology \& Visual Science},
year = {1999},
month = {5},
volume = {40},
number = {4},
pages = {414},
department = {Department B{\"u}lthoff},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {Fort Lauderdale, FL, USA},
event_name = {Annual Meeting of the Association for Research in Vision and Ophthalmology (ARVO 1999)},
author = {Rieger, JW and Gegenfurtner, KR and Braun, C and Preissl, H and B{\"u}lthoff, HH}
}
@Poster { 317,
title = {Comparison of oculometric and psychometric functions for velocity discrimination of chromatic and luminance targets},
journal = {Investigative Ophthalmology \& Visual Science},
year = {1999},
month = {5},
volume = {40},
number = {4},
pages = {427},
department = {Department B{\"u}lthoff},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {Fort Lauderdale, FL, USA},
event_name = {Annual Meeting of the Association for Research in Vision and Ophthalmology (ARVO 1999)},
author = {Scott, BH and Gegenfurtner, KR and Hawken, MJ}
}
@Poster { 1344,
title = {Grasping visual illusions: No difference between perception and action?},
journal = {Investigative Ophthalmology \& Visual Science},
year = {1999},
month = {5},
volume = {40},
number = {4},
pages = {413},
abstract = {PURPOSE: Visually guided motor behavior is assumed
to be rather unreceptive to size illusions,
indicating two different cortical processing
streams for the purposes of perception and action
(e.g., Aglioti, DeSouza \& Goodale, 1995; Current
Biology 5, 679-685). Having shown - in contrary -
that grasping and perception are equally
influenced by the Ebbinghaus / Titchener Illusion
(ECVP 98), we tested whether this is also true for
the Mueller-Lyer Illusion. METHODS: Plastic bars
(40, 43, 46 and 49 mm long, 5 mm wide) were
positioned on top of a horizontally oriented
monitor. Fins were presented on the monitor being
directed either outwards or inwards, such that the
fins and the bars resulted in the Mueller-Lyer
Illusion. In the grasping task, twelve subjects
grasped the bars and the maximal aperture between
thumb and index finger was measured using an
Optotrak (TM) system. In the visual perception
task, the subjects adjusted the length of a
comparison bar on the screen to match the length
of the plastic bars. RESULTS: There were strong
effects of the Mueller-Lyer Illusion on grasping
as well as on visual perception. The effect on
grasping (3.5+-0.5 mm) was even larger than on
perception (2.1+-0.3 mm). CONCLUSIONS: Our
results show that grasping is influenced by visual
illusions, indicating that the motor system is
receptive to visual illusions.},
department = {Department B{\"u}lthoff},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {Fort Lauderdale, FL, USA},
event_name = {Annual Meeting of the Association for Research in Vision and Ophthalmology (ARVO 1999)},
author = {Franz, VH and Fahle, M and Gegenfurtner, KR and B{\"u}lthoff, HH}
}
@Poster { 314,
title = {Time course of adaptation for color discrimination and appearance},
journal = {Investigative Ophthalmology \& Visual Science},
year = {1999},
month = {5},
volume = {40},
number = {4},
pages = {750},
department = {Department B{\"u}lthoff},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {Fort Lauderdale, FL, USA},
event_name = {Annual Meeting of the Association for Research in Vision and Ophthalmology (ARVO 1999)},
author = {Rinner, O and Gegenfurtner, KR}
}
@Poster { 1345,
title = {Der Einfluss von Gr{\"o}{\ss}enillusionen auf das Greifen:
Die M{\"u}ller-Lyer Illusion},
journal = {Experimentelle Psychologie},
year = {1999},
month = {4},
volume = {41},
pages = {96},
abstract = {Auf der TeaP98 hatten wir einen Einfluss der
Ebbinghaus / Titchener Illusion sowohl auf die
Wahrnehmung als auch auf die Greifmotorik
gezeigt. Diese Daten widersprechen der
verbreiteten Auffassung, dass das motorische
System nur in geringem Masse visuellen
Grosssenillusionen unterliegt (Aglioti, DeSouza \&
Goodale, 1995). Damit wird die Theorie in Frage
gestellt, dass im Handlungsund im
Wahrnehmungssystem visuelle Information qualitativ
unterschiedlich verarbeitet wird (Milner \&
Goodale, 1995). In dem vorliegenden Experiment
wurde untersucht, inwieweit sich die Ergebnisse
zur Ebbinghaus Illusion auf die Mueller-Lyer
Taueschung generalisieren lassen. Zwoelf
Versuchspersonen (VPn) wurden Plastikstaebchen
(40, 43, 46 und 49 mm lang, 5 mm breit) auf der
Oberflaeche eines flach liegenden Bildschirmes
dargeboten. Auf dem Bildschirm wurden entweder
nach aussen oder nach innen gerichtete
Pfeilspitzen gezeigt, so dass sich aus Staebchen
und Pfeilspitzen die Mueller-Lyer Taueschung
ergab. Die VPn griffen die Staebchen und die
maximale Handoeffnung vor Beruehrung der Staebchen
wurde mittles eines Optotrak (TM) Systems
ermittelt. In einer zweiten Aufgabe wurde der
Einfluss der Illusion auf die Wahrnehmung mittels
einer Einstell-Prozedur ermittelt. Die Ergebnisse
zeigen starke Einflussse der Illusion sowohl auf
die Wahrnehmung als auch auf das Greifen. Auch
diese Ergebnis widerspricht der Auffassung, dass
das Greifen nur in geringem Masse visuellen
Illusionen unterliege. Interessanterweise ist in
unserem Experiment der Einfluss auf das Greifen
sogar grossser als auf die Wahrnehmung. Gruende
hierfuer werden diskutiert.},
department = {Department B{\"u}lthoff},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {Leipzig, Germany},
event_name = {41. Tagung Experimentell Arbeitender Psychologen (TeaP 1999)},
author = {Franz, VH and Gegenfurtner, KR and B{\"u}lthoff, HH and Fahle, M}
}
@Poster { 311,
title = {Eine MEG-Untersuchung zur R{\"u}ckw{\"a}rtsmaskierung bei der Wiedererkennung nat{\"u}rlicher Szenen},
year = {1999},
month = {2},
pages = {50},
abstract = {R{\"u}ckw{\"a}rtsmaskierung wird in vielen psychophysischen Experimenten eingesetzt und soll die Verarbeitungszeit f{\"u}r einen zeitlich vorangehenden Reiz limitieren. Wir untersuchten die physiologische Basis der visuellen R{\"u}ckw{\"a}rtsmaskierung, indem wir die magnetischen Felder an der Sch{\"a}deloberfl{\"a}che von Versuchspersonen (Vp) aufnahmen,
w{\"a}hrend sie eine Wiedererkennungsaufgabe durchf{\"u}hrten.
Den Vpn wurde in jedem Durchgang auf einem Projektionsschirm kurz (37 ms und 92 ms) Photographien einer nat{\"u}rlichen Szene dargeboten und anschlie{\ss}end f{\"u}r 500 ms eine Maske pr{\"a}sentiert. Danach wurden der Vp gleichzeitig zwei Photographien pr{\"a}sentiert, von denen eine die schon kurz gezeigte war, die andere jedoch eine neue Photographie war. Die Vp wurde angewiesen durch eine Fingerbewegung anzugeben, welches der beiden Bilder sie schon zuvor gesehen hatte (2AFC-Aufgabe). Die Maske war aus Linien und Quadraten zuf{\"a}lliger Gr{\"o}{\ss}e und Orientierung aufgebaut und ihre Farbe wurde aus den beiden Photos des jeweiligen Durchgangs entnommen. In zwei weiteren Bedingungen wurde entweder nur eine Maske oder nur ein Photo ohne eine darauffolgende Maske gezeigt. W{\"a}hrend der Reizdarbietung wurden die evozierten magnetischen Felder mit
einem CTF 151-Kanal MEG-Ganzkopfsystem aufgezeichnet.
Durch die Reduktion der Darbietungsdauer von 92 ms auf 37 ms wurde dieWiedererkennungsleistung der Versuchsperson von 97\% auf 67\% richtiger Antworten herabgesetzt. Die MEG-Daten zeigen, da{\ss} die Aktivit{\"a}t in den ersten 80-120 ms in den Kan{\"a}len {\"u}ber dem okzipitalen Kortex konzentriert ist. Bei langen Darbietungszeiten (92 ms) hatte die Maske keine Wirkung auf die Wiedererkennungleistung der Vp. Bei der kurzen (37 ms) Darbietungszeit kam es jedoch w{\"a}hrend der okzipitalen Verarbeitung des Photos zu einer kurzen Interferenz mit der durch die Maske verursachten okzipitalen Aktivierung. Die Ergebnisse deuten an, da{\ss} neue Information, die innerhalb der ersten 40 ms der kortikalen
Verarbeitung einer nat{\"u}rlichen Szene in den fr{\"u}hen visuellen Arealen eintrifft zu einer starken Reduktion der Wiedererkennungsleistung f{\"u}hren kann. Die Reduktion der
Wiedererkennungsleistung scheint mit der zeitlichen {\"U}berlappung der okzipitalen Aktivierung durch Zielreiz (Photo) und Maske einherzugehen. Auf Verabeitungsstufen, die
sp{\"a}ter als ca. 190 ms nach der Reizpr{\"a}setation aktiviert werden werden, scheint die Maske keinen Einflu{\ss} zu haben.},
url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/pdf311.pdf},
department = {Department B{\"u}lthoff},
web_url = {http://www.twk.tuebingen.mpg.de/twk99/},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {T{\"u}bingen, Germany},
event_name = {2. T{\"u}binger Wahrnehmungskonferenz (TWK 99)},
author = {Rieger, JW and Gegenfurtner, KR and Braun, C and Preissl, H and B{\"u}lthoff, HH}
}
@Poster { 303,
title = {Optische T{\"a}uschungen: Wird die Hand weniger get{\"a}uscht als das Auge?},
year = {1999},
month = {2},
pages = {104},
abstract = {Die prominente “Action vs. Perception” Hypothese von Milner \& Goodale (1995) nimmt an, da{\ss} visuelle Information f{\"u}r die Zwecke von Wahrnehmung und Handlung unterschiedlich
verarbeitet wird. Als starke Evidenz wurden bisher Befunde an optischen T{\"a}uschungen gewertet. So berichteten zum Beispiel Aglioti, DeSouza \& Goodale (1995), da{\ss} Greifen durch optische T{\"a}uschungen kaum beeinflu{\ss}t werde. Im Gegensatz zu diesen Befunden hatten wir einen Einflu{\ss} der Ebbinghaus / Titchener Illusion sowohl auf die
Wahrnehmung als auch auf die Greifmotorik gezeigt. In dem vorliegenden Experiment wurde untersucht, inwieweit dies ebenfalls auf die M{\"u}ller-Lyer T{\"a}uschung zutrifft.
Zw{\"o}lf Versuchspersonen (VPn) wurden Plastikst{\"a}bchen (40, 43, 46 und 49 mm lang, 5 mm breit) auf der Oberfl{\"a}che eines flach liegenden Bildschirmes dargeboten. Auf dem
Bildschirm wurden entweder nach au{\ss}en oder nach innen gerichtete Pfeilspitzen gezeigt, so da{\ss} sich aus St{\"a}bchen und Pfeilspitzen die M{\"u}ller-Lyer T{\"a}uschung ergab. Die VPn
griffen die St{\"a}bchen und die maximale Hand{\"o}ffnung vor Ber{\"u}hrung der St{\"a}bchen wurde mittels eines Optotrak (TM) Systems ermittelt. In einer zweiten Aufgabe wurde der Einflu{\ss} der Illusion auf die Wahrnehmung mittels eines Herstellungsverfahrens ermittelt.
Die Ergebnisse zeigen starke Einfl{\"u}sse der Illusion sowohl auf die Wahrnehmung (2.1 +/ - 0.3 mm) als auch auf das Greifen (3.5 +/- 0.5 mm). Dieses Ergebnis widerspricht der Auffassung, da{\ss} das Greifen nur in geringem Ma{\ss}e
visuellen Illusionen unterliege. Interessanterweise ist in unserem Experiment der Einflu{\ss} auf das Greifen sogar gr{\"o}{\ss}er als auf die Wahrnehmung.},
url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/pdf303.pdf},
department = {Department B{\"u}lthoff},
web_url = {http://www.twk.tuebingen.mpg.de/twk99/},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {T{\"u}bingen, Germany},
event_name = {2. T{\"u}binger Wahrnehmungskonferenz (TWK 99)},
author = {Franz, VH and Gegenfurtner, KR and B{\"u}lthoff, HH and Fahle, M}
}
@Poster { 315,
title = {Zeitverlauf der Adaptation f{\"u}r chromatische Diskrimination und Farberscheinung},
year = {1999},
month = {2},
pages = {57},
abstract = {Chromatische Adaptation ist ein zentraler Mechanismus des Farbensehens, der die Basis f{\"u}r ann{\"a}hernde Farbkonstanz {\"u}ber einen weiten Bereich von Beleuchtungsbedingungen
ist. Ziel unserer Untersuchung war es, den Zeitverlauf der chromatischen Adaptation f{\"u}r Farbunterscheidung und Farberscheinung im Bereich von Millisekunden bis Minuten zu
bestimmen. Uns interessierte, ob der zeitliche Verlauf f{\"u}r die beiden Ph{\"a}nomene, denen gew{\"o}hnlich verschiedene Verarbeitungsebenen zugeschrieben werden, unterschiedlich
ist, und ob sich Unterschiede entlang verschiedener Farbachsen finden lassen. Die Versuchspersonen adaptierten auf einen uniformen Hintergrund, der aus einem
Monitor und einer 60x60 Grad gro{\ss}en Wand aufgebaut war, die mit computergesteuerten Neonlampen beleuchtet wurde. Nach Umschalten des Hintergrunds auf die adaptierende Farbe, die entlang einer der kardinalen rot-gr{\"u}n (L-M) oder blau-gelb (S-(L+M)) Achsen lag, wurden zu definierten Zeitpunkten von 500 ms bis 2 min Adaptationsdauer Reize dargeboten und die Schwellen f{\"u}r jeden Zeitpunkt bestimmt. F{\"u}r die Messung der Zeitabh{\"a}ngigkeit der Farberscheinung wurde mit demselben Verfahren durch Grauwerteinstellung der Zeitverlauf der Farbinduktion bestimmt. Um die schnellen Komponenten der
Adaptation zu messen, wurde ein modifiziertes Paradigma eingesetzt. Die Reize wurden 8 ms bis 500 ms nach Umschalten auf die adaptierende Farbe dargeboten. Readaptation auf die Referenzfarbe erfolgte nach jedem Reiz.
Wir fanden drei Komponenten f{\"u}r den Zeitverlauf der Farberscheinung und chromatischen Diskrimination. Zwei Komponenten, ein langsamer exponentieller Abfall mit einer
Zeitkonstante von 20 - 30 s und ein schneller Mechanismus mit einer Zeitkonstante von 100 - 200 ms, sind Farberscheinung und -unterscheidung gemeinsam. Ausschlie{\ss}lich f{\"u}r die Farberscheinung fanden wir eine extrem schnelle Komponente mit einer Halbwertszeit
von h{\"o}chstens 10 ms, die den {\"u}berwiegenden Anteil der Gesamtadaptation ausmacht. F{\"u}r L-M und S-(L+M) Achse ergaben sich keine systematischen Unterschiede. Wir schlie{\ss}en aus den Ergebnissen, da{\ss} der schnellste chromatische Adaptationsmechanismus, der sich nur f{\"u}r die Farberscheinung finden l{\"a}{\ss}t, nicht auf einer unteren Verarbeitungsebene angesiedelt ist, sondern Te il eines h{\"o}heren Verarbeitungsmechanismus ist.},
url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/pdf315.pdf},
department = {Department B{\"u}lthoff},
web_url = {http://www.twk.tuebingen.mpg.de/twk99/},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {T{\"u}bingen, Germany},
event_name = {2. T{\"u}binger Wahrnehmungskonferenz (TWK 99)},
author = {Rinner, O and Gegenfurtner, KR}
}
@Poster { D039ZmuraRG1998,
title = {Colour and lightness of a surface seen behind a transparent filter},
journal = {Perception},
year = {1998},
month = {8},
volume = {27},
number = {ECVP Abstract Supplement},
pages = {170},
abstract = {We measured how the colour and lightness of a surface seen to lie behind a transparent filter depend on filter properties. A convergence model suggests that a filter's transformation of chromatic information from underlying surfaces is interpreted as a convergence in colour space (D'Zmura, Colantoni, Knoblauch, and Laget, 1997 Perception 26 471 - 492). Such a convergence is described by a transparency parameter alpha and by a colour that acts as the centre of convergence.
We used an asymmetric matching task to test the model. In computer-graphic simulation, observers adjusted the colour of a surface seen behind a transparent colour filter in order to match the colour of a surface seen in plain view. We varied the lightness and chromatic properties of both the surface to be matched and the transparent filter. We found that the convergence model fitted the matching data nearly as well as a more general affine transformation model, even though the latter has many more parameters (twelve) than the former (four). Linear transformation, translation, and Von Kries scaling models all performed poorly.
The convergence model of transparency is a general model of colour constancy. It can account for shifts in colour, such as those caused by changing the spectral properties of illumination, and can also account for shifts in contrast, like those caused by fog or by change in the spatial distribution of illumination.},
department = {Department B{\"u}lthoff},
web_url = {http://www.perceptionweb.com/abstract.cgi?id=v980274},
event_place = {Oxford, UK},
event_name = {21st European Conference on Visual Perception},
author = {D'Zmura, M and Rinner, O and Gegenfurtner, K}
}
@Poster { GegenfurtnerBRPSS1998,
title = {Selective colour constancy deficits after unilateral brain lesion},
journal = {Perception},
year = {1998},
month = {8},
volume = {27},
number = {ECVP Abstract Supplement},
pages = {181},
abstract = {To gain insight into the neural basis of colour constancy, we examined the colour vision of twenty-seven patients with defined unilateral lesions mainly located in the parieto-temporo-occipital cortex. Patients were tested with a battery of vision and colour vision tests. Detection and grouping thresholds for isoluminant chromatic and for luminance stimuli were measured to assess retinal and early cortical processing. To examine higher cortical functions, we tested colour memory, colour - object association, and colour constancy. For the evaluation of colour constancy, subjects had to adjust the colour of a test field until it appeared as neutral gray. The test field was embedded amid a set of coloured patches, and the illuminant was varied from trial to trial. A control group of healthy subjects was tested in the same tasks.
Five of the twenty-seven patients showed a selective deficit in the colour constancy tests. All five patients showed normal colour discrimination. A comparison with anatomical lesion data, based on CT- or MRI-scans, showed that one of the five patients had a lesion near the fusiform and lingual gyri, whose importance for colour constancy had been suggested in earlier studies. However, three other patients had overlapping lesions in a region of parieto-temporal cortex, which so far had not been associated with colour vision. These results indicate that the computations underlying colour constancy are mediated by specialised cortical circuitry, which is independent of the neural substrate for colour discrimination and for assigning colours to objects.},
department = {Department B{\"u}lthoff},
web_url = {http://www.perceptionweb.com/abstract.cgi?id=v980162},
event_place = {Oxford, UK},
event_name = {21st European Conference on Visual Perception},
author = {Gegenfurtner, KR and Braun, DI and R{\"u}ttiger, L and Petersen, D and Sch{\"o}nle, P and Sharpe, LT}
}
@Poster { 1348,
title = {Size-contrast illusions deceive grasping as well as perception},
journal = {Perception},
year = {1998},
month = {8},
volume = {27},
number = {ECVP Abstract Supplement},
pages = {140},
abstract = {Size contrast illusions are assumed to exert a
smaller effect on human motor behavior than on
perception, indicating different cortical pathways
for perception and action (e.g., Aglioti, DeSouza\& Goodale, 1995 Current Biology 5 679-685). We
tried to replicate these findings for the
Ebbinghaus Illusion. Special effort was taken to
minimize effects of motor learning and on
assessment of the size of the perceptual illusion.
An aluminum disc (28, 31, 34 or 37 mm in diameter,
5 mm in height) was positioned as target on a
board. Around the target either small or large
context discs were drawn (10 or 58 mm in
diameter). Close to the board a monitor was
mounted on which a comparison disc was
displayed. In a visual task twelve subjects
adjusted the size of the comparison disc to match
the size of the target. In a grasping task
subjects grasped the target. Subjects wore shutter
glasses and could not see their hand during
grasping (open loop condition). The grasp
trajectory was recorded and the maximum preshape
aperture was calculated. Preshape aperture and
adjusted size showed strong and similar linear
relationships to the size of the target. The mean
perceptual effect of the illusion was 1.4 mm (SE =
0.1 mm) while the effect of the illusion on
preshape aperture was 1.5 mm (SE = 0.4 mm). Thus,
grasping was just as much influenced by the
illusion as perception. Possible reasons for this
discrepancy to previous studies are discussed.},
department = {Department B{\"u}lthoff},
web_url = {http://www.perceptionweb.com/abstract.cgi?id=v980014},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {Oxford, UK},
event_name = {21st European Conference on Visual Perception},
author = {Franz, VH and Fahle, M and Gegenfurtner, KR and B{\"u}lthoff, HH}
}
@Poster { RiegerG1998_2,
title = {The relationship between perceived brightness and contrast threshold in illusory figures},
journal = {Perception},
year = {1998},
month = {8},
volume = {27},
number = {ECVP Abstract Supplement},
pages = {90-91},
abstract = {We investigated the relationship between changes in contrast thresholds on illusory contours and the brightness changes perceived on these contours.
We measured the perceived brightness in the gaps of a Kanizsa square, where an illusory figure is perceived, and in the gaps of an outline square by determining the point of subjective equality with the background for a small line target presented in the gap. White inducers were displayed on a gray background. We also determined the decrement and increment thresholds for detecting the same target in these two configurations. While the gap appeared to be brighter than the background, there was no significant difference between increment and decrement thresholds, which means that the perceived brightness in the gap does not act like a simple contrast pedestal on the detection of the target. This implies that brightness and luminance are processed at different levels.
To investigate possible top - down influences of figural completion we compared the increment thresholds obtained in a closed configuration (same as above) to thresholds in an open configuration where only two sides of the square were outlined by the inducers. Contrast thresholds for both configurations were significantly lower than in the control configuration, where the target was displayed alone. We found no difference in increment thresholds between the open and the closed configuration, which suggests that later processing stages, in which the unity of the square is established, have no influence on contrast thresholds.},
department = {Department B{\"u}lthoff},
web_url = {http://www.perceptionweb.com/abstract.cgi?id=v980265},
event_place = {Oxford, UK},
event_name = {21st European Conference on Visual Perception},
author = {Rieger, JW and Gegenfurtner, K}
}
@Poster { 284,
title = {Contrast thresholds and perceived brightness in contour gaps},
year = {1998},
month = {5},
volume = {26},
pages = {84},
department = {Department B{\"u}lthoff},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {G{\"o}ttingen, Germany},
event_name = {26th G{\"o}ttingen Neurobiology Conference},
author = {Rieger, JW and Gegenfurtner, KR}
}
@Poster { 1349,
title = {Grasping isoluminant objects},
journal = {Investigative Ophthalmology and Visual Science},
year = {1998},
month = {5},
volume = {39},
number = {4},
pages = {1095},
department = {Department B{\"u}lthoff},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {Fort Lauderdale, FL, USA},
event_name = {Annual Meeting of the Association for Research in Vision and Ophthalmology (ARVO 1998)},
author = {Franz, VH and Gegenfurtner, KR and B{\"u}lthoff, HH and Fahle, M}
}
@Poster { 1350,
title = {T{\"a}uschen Gr{\"o}{\ss}enillusionen sowohl die Hand wie das Auge?},
journal = {Experimentelle Psychologie},
year = {1998},
month = {4},
volume = {40},
pages = {80},
abstract = {Visuelle Groessenillusionen sollen auf die
Greifmotorik einen deutlich geringeren Einluss
ausueben als auf die Wahrnehmung (Aglioti, DeSouza\& Goodale, 1995). Dies wird als Indiz dafuer
gewertet, dass Information ueber visuelle Grossse
vom Wahrnehmungs- und vom Handlungssystem
unabhaengig ausgewertet werden. In dem
vorliegenden Experiment sollte diese Hypthese
ueberprueft werden. Insbesondere sollten moegliche
Artefakte durch motorisches Lernen vermieden
werden. Sechzehn Versuchspersonen (VPn) wurden
Scheiben mittels Bildschirm und Stereobrille
virtuell dargeboten. Eine zentrale Scheibe war von
fuenf grossen bzw. kleinen Kontext-Scheiben
umgeben, so dass sich die Ebbinghaus Illusion
ergab: Bei grossen Kontext-Scheiben wird die
zentrale Scheibe kleiner, bei kleinen
Kontext-Scheiben groesser wahrgenommen. Der
Durchmesser der zentrale Scheibe variierte von 27
bis 37 mm, in 2 mm Schritten. Die Wahrnehmung der
virtuellen zentrale Scheibe deckte sich in der
raeumlichen Ausdehnung mit einer realen Scheibe,
die jedoch hinter einem Spiegel lag und daher von
den VPn nicht gesehen wurde. Die VP fuehrte eine
Greifbewegung nach der virtuellen Scheibe durch
und erhielt haptisches Feedback durch die reale
Scheibe. Mittels eines Optotrak (TM) - Systems
wurde die maximale Handoeffnung vor Beruehrung der
Scheibe gemessen. Der Einfluss der Illusion auf
die Wahrnehmung wurde ueber eine Einstell-Prozedur
ermittelt. Im Widerspruch zu den Ergebnissen von
Aglioti et. al. fanden wir sowohl fuer die
wahrgenommene Groesse als auch fuer die maximale
Griffgroesse einen Einfluss der Illusion. Dies
legt nahe, dass die gleichen Signale sowohl fuer
Handlung als auch fuer die Wahrnehmung benutzt
werden. Verschiedene Erklaerungen fuer diesen
Widerspruch werden anhand von Kontrollexperimenten
diskutiert.},
department = {Department B{\"u}lthoff},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {Marburg, Germany},
event_name = {40. Tagung Experimentell Arbeitender Psychologen (TeaP 1998)},
author = {Franz, VH and Gegenfurtner, KR and B{\"u}lthoff, HH and Fahle, M}
}
@Poster { 273,
title = {Einflu{\ss} der Gr{\"o}{\ss}e bekannter Objekte auf Geschwindigkeitskonstanz},
year = {1998},
month = {2},
pages = {48},
abstract = {Geschwindigkeitskonstanz ist die F{\"a}higkeit des Menschen, die physikalische Geschwindigkeit von Objekten, die sich in unterschiedlicher Entfernung vom Beobachter bewegen,
korrekt einzusch{\"a}tzen. Es ist bekannt, da{\ss} die Gr{\"o}{\ss}e der Objekte einen sehr starken Einflu{\ss} auf die wahrgenommene Geschwindigkeit aus{\"u}bt. In unserem ersten Experiment
haben wir unter Verwendung von bekannten Objekten den Einflu{\ss} der Gr{\"o}{\ss}e auf die Geschwindigkeitskonstanz genauer untersucht. Im zweiten Experiment haben wir getestet,
inwieweit Vorwissen {\"u}ber die Geschwindigkeit und Gr{\"o}{\ss}e der Objekte im Alltag (Auto versus Lkw) in die Einsch{\"a}tzung ihrer Geschwindigkeit einbezogen wird.
In einem 2-AFC Paradigma wurden Versuchspersonen 3D-Computer-Grafikmodelle zweier Fahrzeuge pr{\"a}sentiert, die links und rechts von der Bildschirmmitte versetzt
waren und sich in Richtung der Bildschirmmitte bewegten. Die beiden Fahrzeuge wurden f{\"u}r eine Sekunde auf einer zylinderf{\"o}rmigen Gro{\ss}bildleinwand (Durchmesser: 7 m,
H{\"o}he: 3.15 m) mit einem Gesichtsfeld von 180x50 Grad dargestellt. Aufgabe der Versuchspersonen war es zu entscheiden, welches der beiden Fahrzeuge schneller f{\"a}hrt.
Dabei wurde eines dieser beiden Fahrzeuge, das Standard-Fahrzeug, w{\"a}hrend eines jeden Versuchsdurchganges in einer simulierten Beobachter-Objekt Entfernung von 20 m dargestellt und bewegte sich mit einer konstanten Geschwindigkeit von 3.0 m/s (10.8 km/h).
Die Test-Fahrzeuge wurden in drei Entfernungen (10, 20 und 40 m) pr{\"a}sentiert. Ihre Geschwindigkeit wurde mittels eines adaptiven Schwellenverfahrens bestimmt. Im ersten
Experiment wurden Test-Fahrzeuge vom gleichen Typ in drei verschiedenen Gr{\"o}{\ss}en (50, 100 und 200\% Gr{\"o}{\ss}e des Standards) verwendet. Im zweiten Experiment wurden drei verschiedene
Test-Fahrzeuge eingesetzt: ein Auto normaler Gr{\"o}{\ss}e, ein Lkw (280\% Gr{\"o}{\ss}e des Standards) und einen {\"u}bergro{\ss}es Auto in der Gr{\"o}{\ss}e des Lkw.
Bei gleicher Entfernung zweier Fahrzeuge betr{\"a}gt die wahrgenommene Geschwindigkeit eines doppelt so gro{\ss}en Fahrzeuges 88\% der Geschwindigkeit eines Fahrzeuges normaler
Gr{\"o}{\ss}e (10m: 86\%, 20m: 86\%, 40m: 92\%). Bei halber Gr{\"o}{\ss}e des Fahrzeuges betr{\"a}gt die Geschwindigkeit 126\% (10m: 125\%, 20m: 124\%, 40m: 128\%). Die wahrgenommene Geschwindigkeit des Lkw liegt bei 86\% der Geschwindigkeit des normal gro{\ss}en Fahrzeuges, w{\"a}hrend die wahrgenommene Geschwindigkeit des {\"u}bergro{\ss}en Fahrzeuges 72\% der Geschwindigkeit des normal gro{\ss}en Fahrzeuges betr{\"a}gt.
Die Gr{\"o}{\ss}e von Objekten {\"u}bt unabh{\"a}ngig von der Entfernung der Objekte auch bei bekannten Objekten einen sehr starken Einflu{\ss} auf die wahrgenommene Geschwindigkeit aus. Je gr{\"o}{\ss}er ein Objekt ist, desto langsamer wird es wahrgenommen. Weiterhin wird aber auch Vorwissen {\"u}ber Geschwindigkeit und Gr{\"o}{\ss}e des Objektes im Alltag bei der
Einsch{\"a}tzung seiner Geschwindigkeit ber{\"u}cksichtigt, da ein Lkw schneller als ein Auto gleicher Gr{\"o}{\ss}e wahrgenommen wird.},
department = {Department B{\"u}lthoff},
web_url = {http://www.twk.tuebingen.mpg.de/twk98/},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {T{\"u}bingen, Germany},
event_name = {1. T{\"u}binger Wahrnehmungskonferenz (TWK 98)},
author = {Distler, HK and Gegenfurtner, KR}
}
@Poster { ReisbeckG1998,
title = {Geschwindigkeitssensitive Mechanismen bei der
menschlichen Bewegungswahrnehmung},
year = {1998},
month = {2},
pages = {47},
abstract = {Die neuronalen Mechanismen zur Verarbeitung von Bewegungsrichtung sind schon sehr genau charakterisiert.Weitgehend ungekl{\"a}rt sind jedoch noch die neuronalen Grundlagen der Geschwindigkeitswahrnehmung. Wir untersuchten, ob es selektive Mechanismen gibt, die f{\"u}r die Ermittlung der Objektgeschwindigkeit verantwortlich sind.
Dazu wurden zweidimensionale Unterscheidungskonturen in der Ebene, die durch Orts und Zeitfrequenz aufgespannt wird, bestimmt. Die Form dieser Konturen gibt dar{\"u}ber Aufschlu{\ss}, ob in der Bewegungswahrnehmung geschwindigkeitssensitive Mechanismen oder separable Mechanismen bez{\"u}glich Orts- und Zeitfrequenz realisiert sind. Versuchspersonen wurden 4 Reize dargeboten, von denen drei (Standards) dieselbe Orts- und Zeitfrequenz aufwiesen und einer sich in einem bestimmten Verh{\"a}ltnis von Orts- zu Zeitfrequenz (Test) von den Standards unterschied. Die Versuchspersonen mu{\ss}ten angeben, welches der Testreiz war.
Die Schwellenkonturen waren deutlich entlang einer Achse konstanter Geschwindigkeit ausgerichtet. Das ist eine systematische und signifikante Abweichung von der Vorhersage
f{\"u}r separable Mechanismen bez{\"u}glich Orts- und Zeitfrequenz. Um die verantwortlichen Mechanismen zu isolieren, wurden zwei Arten von Rauschen zu den Standardreizen addiert: zum einen entlang einer Achse konstanter Geschwindigkeit und zum anderen entlang einer dazu senkrechten Achse. Die Rauschamplitude in Bezug auf Orts- und Zeitfrequenz
war in beiden F{\"a}llen gleich. Im ersten Fall kam es zu einer deutlichen Verl{\"a}ngerung der Kontur entlang der Achse konstanter Geschwindigkeit, im anderen Fall kam es
zu einem allgemeinen Anstieg der Unterscheidungsschwellen. Dies bedeutet, da{\ss} es Mechanismen gibt, die selektiv Information {\"u}ber die Geschwindigkeit extrahieren.},
department = {Department B{\"u}lthoff},
web_url = {http://www.twk.tuebingen.mpg.de/twk98/},
event_place = {T{\"u}bingen, Germany},
event_name = {1. T{\"u}binger Wahrnehmungskonferenz (TWK 98)},
author = {Reisbeck, TE and Gegenfurtner, KR}
}
@Poster { 275,
title = {Greifen als Test f{\"u}r die Unterscheidung von Wahrnehmung und Handlung},
year = {1998},
month = {2},
pages = {162},
abstract = {In der Literatur wird angenommen, dass die Verarbeitung visueller Information fuer die Zwecke von Wahrnehmung und Handlung unterschiedlich verlaueft. Diese Unterscheidung soll sich bei gesunden Personen darin zeigen, dass
Grosssenillusionen auf die Greifmotorik einen deutlich geringeren Einluss ausueben als auf die Wahrnehmung (Aglioti, DeSouza \& Goodale, 1995; Brenner \& Smeets, 1996). Zur Ueberpruefung der Hypothese wurde eine virtuelle
Untersuchungsapparatur verwendet, die eine weitgehende Manipulation der visuellen Information gestattet. Mit dieser Apparatur liessen sich Stoervariablen besser als in vorherigen Studien kontrollieren. Sechzehn Versuchspersonen (VPn) wurden Scheiben mittels Bildschirm und Stereobrille virtuell dargeboten. Eine zentrale
Scheibe war von fuenf grossen bzw. kleinen
Kontext-Scheiben umgeben, so dass sich die Ebbinghaus Illusion ergab: Bei grossen Kontext-Scheiben wird die zentrale Scheibe kleiner, bei kleinen Kontext-Scheiben grossser wahrgenommen. Der Durchmesser der zentrale Scheibe
variierte von 27 bis 37 mm, in 2 mm Schritten. Die
Wahrnehmung der virtuellen zentrale Scheibe deckte sich in der rauemlichen Ausdehnung mit einer realen Scheibe, die jedoch hinter einem Spiegel lag und daher von den VPn nicht gesehen wurde. Die VP fuehrte eine Greifbewegung nach der virtuellen Scheibe durch und erhielt haptisches Feedback
durch die reale Scheibe. Mittels eines Optotrak -
Systems wurde die maximale Handoeffnung vor
Ber{\"u}hrung der Scheibe gemessen. Der Einfluss der
Illusion auf die Wahrnehmung wurde ueber eine Einstell - Prozedur ermittelt. Wir fanden sowohl fuer die wahrgenommene Groesse als auch fuer die maximale Griffgroesse einen Einfluss der Illusion. Dieses Ergebnis steht im Widerspruch zu den Ergebnissen in der Literatur. Gruende fuer diese Diskrepanz werden diskutiert.},
department = {Department B{\"u}lthoff},
web_url = {http://www.twk.tuebingen.mpg.de/twk98/},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {T{\"u}bingen, Germany},
event_name = {1. T{\"u}binger Wahrnehmungskonferenz (TWK 98)},
author = {Franz, VH and Gegenfurtner, KR and B{\"u}lthoff, HH and Fahle, M}
}
@Poster { RiegerG1998,
title = {Subjektive Helligkeit und Kontrastschwellen in Konturl{\"u}cken},
year = {1998},
month = {2},
pages = {139},
abstract = {Kontur (Dresp \& Bonnet, 1995), als auch auf einem unterschwelligen Kontrastsockel (Foley \& Legge, 1981) herabgesetzt sein k{\"o}nnen. Das l{\"a}{\ss}t die Frage offen, ob die Kontrastschwellen durch unterschwellige Summation der subjektiven Helligkeit mit der objektiven Helligkeit des Testreizes reduziert werden.
Um die Kontrastschwellen f{\"u}r einen Testreiz zu bestimmen, mu{\ss}ten die Versuchspersonen entscheiden, in welcher von zwei gegen{\"u}berliegenden Konturl{\"u}cken eines Quadrats
er dargestellt wurde. Wir verwendeten drei Reizkonfigurationen: (1) Ein Kanizsa-Quadrat, bei dem eine illusion{\"a}re Kontur wahrgenommen wird, (2) ein Quadrat aus unterbrochenen Linien und (3) eine Kontrollbedingung, bei der der Testreiz alleine dargestellt wurde.
Subjektive Helligkeit: Bei kurzen Darbietungszeiten werden illusion{\"a}re Helligkeitsunterschiede nicht nur im Kanizsa-Quadrat, sondern auch zwischen Liniensegmenten wahrgenommen.
Um die St{\"a}rke der empfundenen Helligkeit zu messen, bestimmten wir f{\"u}r den Testreiz den Punkt subjektiver Gleichheit mit dem Hintergrund (PsG). Bei den Liniensegmenten wurde der PsG des Testreizes im Mittel um 4,8\% Weber-Kontrast unter die Hintergrundluminanz
verschoben. Beim Kanizsa-Quadrat betrug die Verschiebung 3,9\% Weber-Kontrast. Zus{\"a}tzlich bestimmten wir unter den gleichen Bedingungen die Inkrement- und die Dekrementschwellen f{\"u}r den Testreiz.Wir fanden keinen Unterschied zwischen den Inkrement- und den Dekrementschwellen. Verhielte sich die subjektive Helligkeit
aber gleich wie die objektive, w{\"a}re zu erwarten, da{\ss} die Dekrementschwellen erh{\"o}ht sind. Subjektive Helligkeit und Kontrastschwellenreduktion sind daher unabh{\"a}ngige Ph{\"a}nomene.
Offene und geschlossene Figuren: In einem weiteren Experiment {\"u}berpr{\"u}ften wir, ob die Reduktion der Kontrastschwellen durch lokale Prozesse, die die Konturl{\"u}cken {\"u}berbr{\"u}kken, verursacht wird. Es w{\"a}re denkbar, da{\ss} auch globale Prozesse, die erst wirksam werden
k{\"o}nnen nachdem das Quadrat vollst{\"a}ndig etabliert ist, einen Einflu{\ss} haben. In der offenen Bedingung wurden die Konturelemente des Kanizsa-Quadrats und des Quadrats
aus Linien so ver{\"a}ndert, da{\ss} die Figur nicht mehr zu einem Quadrat vervollst{\"a}ndigt werden konnte. Wir fanden keinen Unterschied zwischen den Kontrastschwellen der offenen
und der geschlossenen Bedingung. Das zeigt, da{\ss} Prozesse, die Kontrastschwellen erniedrigen, lokal wirksam sind und von nachfolgenden Prozessen, in denen die Konturelemente
zum Quadrat integriert werden, unbeeinflu{\ss}t bleiben.},
department = {Department B{\"u}lthoff},
web_url = {http://www.twk.tuebingen.mpg.de/twk98/},
event_place = {T{\"u}bingen, Germany},
event_name = {1. T{\"u}binger Wahrnehmungskonferenz (TWK 98)},
author = {Rieger, JW and Gegenfurtner, KR}
}
@Poster { 395,
title = {Cortical and subcortical inputs to macaque area V3},
year = {1997},
month = {10},
volume = {27},
pages = {1032},
department = {Department B{\"u}lthoff},
web_url = {http://www.sfn.org/index.aspx?pagename=annualmeeting_futureandpast},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {New Orleans, LA, USA},
event_name = {27th Annual Meeting of the Society for Neuroscience (Neuroscience 1997)},
author = {Angelucci, A and Levitt, JB and Gegenfurtner, KR and Reisbeck, TE and Lund, JS}
}
@Poster { 405,
title = {Color in the recognition of natural scenes},
journal = {Investigative Ophthalmology \& Visual Science},
year = {1997},
month = {5},
volume = {38},
number = {4},
pages = {900},
department = {Department B{\"u}lthoff},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {Fort Lauderdale, FL, USA},
event_name = {Annual Meeting of the Association for Research in Vision and Ophthalmology (ARVO 1997)},
author = {Gegenfurtner, KR}
}
@Poster { 418,
title = {Human motion perception: Velocity based or space-time separable mechanisms?},
journal = {From Membrane to Mind},
year = {1997},
month = {5},
pages = {565},
department = {Department B{\"u}lthoff},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {G{\"o}ttingen, Germany},
event_name = {25th G{\"o}ttingen Neurobiology Conference},
author = {Reisbeck, TE and Gegenfurtner, KR}
}
@Poster { 402,
title = {Velocity constancy in virtual reality environments},
journal = {Investigative Ophthalmology \& Visual Science},
year = {1997},
month = {5},
volume = {38},
number = {4},
pages = {76},
department = {Department B{\"u}lthoff},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {Fort Lauderdale, FL, USA},
event_name = {Annual Meeting of the Association for Research in Vision and Ophthalmology (ARVO 1997)},
author = {Distler, HK and Gegenfurtner, KR and van Veen, HAHC and Hawken, MJ}
}
@Poster { 419,
title = {Velocity tuned mechanisms in human motion perception},
journal = {Investigative Ophthalmology \& Visual Science},
year = {1997},
month = {5},
volume = {38},
number = {4},
pages = {376},
department = {Department B{\"u}lthoff},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {Fort Lauderdale, FL, USA},
event_name = {Annual Meeting of the Association for Research in Vision and Ophthalmology (ARVO 1997)},
author = {Reisbeck, TE and Gegenfurtner, KR}
}
@Poster { 588,
title = {Colour mechanisms in patients with cortical lesions},
journal = {Vision Research},
year = {1996},
month = {10},
volume = {36},
number = {Supplement},
pages = {S57},
department = {Department B{\"u}lthoff},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {Montpellier, France},
event_name = {Joint European Research Meetings in Ophthalmology and Vision (JERMOV 96)},
author = {R{\"u}ttiger, L and Braun, D and Gegenfurtner, KR and Sch{\"o}nle, P and Sharpe, LT}
}
@Poster { 532,
title = {A comparison of grasping real and virtual objects},
journal = {Perception},
year = {1996},
month = {9},
volume = {25},
number = {ECVP Abstract Supplement},
pages = {92-93},
abstract = {We investigated whether computer-generated stereo projected images (virtual objects) are suitable as targets in grasping experiments. For real and virtual objects we measured grasp quality, movement time, preshape aperture, and terminal aperture angle under two different conditions: (a) block presentation of virtual and real objects and (b) mixed presentation (real and virtual objects interspersed). Maximal number of consecutive presentations of virtual objects was limited to seven under the mixed condition. Six subjects took part in condition (a) and ten subjects in condition (b). Objects had a smooth spline-based contour with a limited number of stable grasp points. Six objects were presented in six different orientations and each grasp was repeated five times.
We found that in block presentation mode grasp quality was generally lower for virtual objects (43\%) than for real objects (78\%). Analysis of the time course revealed that grasp quality was initially the same for both types of objects, but decreased for virtual objects during the course of the experiment. In mixed presentation mode, no such difference was found: grasp quality was equally high for both object types (75\%). No significant differences in movement time and other dynamic parameters were found.
One of the major differences between the two conditions is the lack of haptic feedback for virtual objects in block presentation mode. We argue that missing haptic feedback for virtual objects leads to pantomiming and decreased grasp quality. Haptic feedback is necessary for maintaining grasp quality at a stable level.},
department = {Department B{\"u}lthoff},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {Strasbourg, France},
event_name = {19th European Conference on Visual Perception},
author = {Opitz, D and Gegenfurtner, KR and B{\"u}lthoff, HH}
}
@Poster { 587,
title = {Interpolation of real and illusory contours},
journal = {Brain and Evolution},
year = {1996},
month = {5},
volume = {2},
pages = {430},
department = {Department B{\"u}lthoff},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {G{\"o}ttingen, Germany},
event_name = {24th G{\"o}ttingen Neurobiology Conference},
author = {Rieger, JW and Gegenfurtner, KR}
}
@Poster { 585,
title = {Orientation discrimination of luminance and isoluminant stimuli},
journal = {Brain and Evolution},
year = {1996},
month = {5},
volume = {2},
pages = {429},
department = {Department B{\"u}lthoff},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {G{\"o}ttingen, Germany},
event_name = {24th G{\"o}ttingen Neurobiology Conference},
author = {Reisbeck, TE and Gegenfurtner, KR}
}
@Poster { 577,
title = {A comparison of neuronal properties in macaque areas V2 and V3},
journal = {Investigative Ophthalmology \& Visual Science},
year = {1996},
month = {4},
volume = {37},
number = {3},
pages = {482},
department = {Department B{\"u}lthoff},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {Fort Lauderdale, FL, USA},
event_name = {Annual Meeting of the Association for Research in Vision and Ophthalmology (ARVO 1996)},
author = {Kiper, DC and Gegenfurtner, KR and Levitt, JB and Fenstemaker, SB}
}
@Poster { 569,
title = {Localization and identification of shapes defined by real or illusory contours},
journal = {Investigative Ophthalmology \& Visual Science},
year = {1996},
month = {4},
volume = {37},
number = {3},
pages = {174},
abstract = {Purpose: To determine spatial and temporal characteristics of mechanisms that bridge gaps between line segments. Methods: The presentation time was measured which was necessary for localization and identification of a triangular shape made up of (a) pacmen, (b) pacmen with extended lines, (c) lines, (d) corners or (e) pacmen with circles (see Figure). The triangle was embedded in a field of distractors of the same components at random orientations. Subjects had to indicate whether the triangle was left or right of the midline (localization) and pointing up or down (identification). Poststimulus masks consisted of pinwheels (a, b, e) or random lines (c, d). Stimuli were presented on a gray background and defined by luminance or isoluminant contrast. Results: Thresholds for identification were fastest when the triangle was defined by real contours (b: 98 msec; c: 106 msec), slightly slower for corners and pacmen (d: 129 msec; a: 157 msec), and much slower for the amodally completed pacmen (e: 359 msec). For all pattern types localization was about 20 msec faster than identification. Compared to low contrast luminance stimuli, processing of isoluminant stimuli was equally fast for targets defined by real contours (c), but much slower for illusory contours (a). Conclusions: Since processing is faster for corners than for pacmen, bridging line gaps is not dependent on the formation of illusory contours.},
department = {Department B{\"u}lthoff},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {Fort Lauderdale, FL, USA},
event_name = {Annual Meeting of the Association for Research in Vision and Ophthalmology (ARVO 1996)},
author = {Gegenfurtner, KR and Brown, JE and Rieger, JW}
}
@Poster { 573,
title = {Motion of second order stimuli: Smooth pursuit eye movements and perceived speed},
journal = {Investigative Ophthalmology \& Visual Science},
year = {1996},
month = {4},
volume = {37},
number = {3},
pages = {741},
department = {Department B{\"u}lthoff},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {Fort Lauderdale, FL, USA},
event_name = {Annual Meeting of the Association for Research in Vision and Ophthalmology (ARVO 1996)},
author = {Hawken, MJ and Gegenfurtner, KR}
}
@Poster { 586,
title = {Orientation perception for luminance and isoluminant stimuli},
journal = {Investigative Ophthalmology \& Visual Science},
year = {1996},
month = {4},
volume = {37},
number = {3},
pages = {1073},
department = {Department B{\"u}lthoff},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {Fort Lauderdale, FL, USA},
event_name = {Annual Meeting of the Association for Research in Vision and Ophthalmology (ARVO 1996)},
author = {Reisbeck, TE and Gegenfurtner, KR}
}
@Poster { 1140,
title = {Colour in Recognition Memory and Image Understanding},
journal = {Investigative Ophthalmology \& Visual Sciences},
year = {1995},
month = {5},
volume = {36},
number = {4},
pages = {S14},
department = {Department B{\"u}lthoff},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {Fort Lauderdale, FL, USA},
event_name = {Annual Meeting of the Association for Research in Vision and Ophthalmology (ARVO 1995)},
author = {Wichmann, FA and Gegenfurtner, KR}
}
@Conference { Gegenfurtner1998,
title = {Colour mechanisms: from retina to cortex},
journal = {Perception},
year = {1998},
month = {8},
day = {26},
volume = {27},
number = {ECVP Abstract Supplement},
pages = {25},
abstract = {Over the last twenty years, our understanding of colour vision has advanced significantly. In this talk I review some of the important developments during that time.},
department = {Department B{\"u}lthoff},
talk_type = {Abstract Talk},
web_url = {http://www.perceptionweb.com/abstract.cgi?id=v980549},
event_place = {Oxford, UK},
event_name = {21st European Conference on Visual Perception},
author = {Gegenfurtner, K}
}
@Conference { 584,
title = {Orientation discrimination at isoluminance},
journal = {Perception},
year = {1996},
month = {9},
volume = {25},
number = {ECVP Abstract Supplement},
pages = {53},
abstract = {Colour and form are important attributes of the objects in our visual environment. We tested the hypothesis that colour and orientation are processed independently in the visual system. Orientation perception for stimuli defined by luminance is characterised by a decrease in thresholds with increasing stimulus contrast, and by a strong oblique effect: stimuli along the horizontal or vertical axes are discriminated more easily.
We determined orientation discrimination thresholds for stationary, slow (1 Hz) or fast (8 Hz) moving sine-wave gratings (1 cycle deg-1) defined by luminance or isoluminant (red -- green) contrast. In a 4AFC paradigm, three of four stimulus patches were identical and the fourth differed in orientation, contrast, or in both. When we measured orientation discrimination thresholds as a function of stimulus contrast, thresholds decreased for all stimuli with increasing contrast. At all temporal frequencies the functions relating orientation thresholds to stimulus contrast had similar shapes for luminance and isoluminant gratings. On a cone-contrast metric, thresholds for stationary and slowly moving stimuli were consistently lower for isoluminant compared to luminance stimuli. For fast-moving stimuli orientation thresholds were similar for both kinds of gratings. For both types of stimuli a marked oblique effect was observed. To characterise processing of contrast and orientation completely, we measured simultaneous thresholds for contrast and orientation. The shapes of the resulting two-dimensional threshold contours were similar for luminance and isoluminant gratings, indicating similar rules for combining differences in contrast and orientation. We conclude that processing of isoluminant and luminance stimuli undergoes the same neural processing at least for the low spatial frequencies used here.},
department = {Department B{\"u}lthoff},
talk_type = {Abstract Talk},
web_url = {http://www.perceptionweb.com/abstract.cgi?id=v96l1202},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {Strasbourg, France},
event_name = {19th European Conference on Visual Perception},
author = {Reisbeck, TE and Gegenfurtner, KR}
}
@Conference { 1141,
title = {The contribution of colour to recognition memory in normal and colour-deficient observers},
journal = {Perception},
year = {1995},
month = {8},
volume = {24},
number = {ECVP Abstract Supplement},
pages = {12-13},
abstract = {The role of chromatic information in visual cognition is still unclear. Considerable neural resources appear to be devoted to the analysis of chromatic information. Yet roughly 8\% of the male population are at least partially colour blind and many remain unaware of their deficiency until formally tested. We used a recognition task to assess the importance of colour information for recognition memory. During the presentation phase a series of 48 images of natural scenes was presented to subjects on a CRT display for exposure durations between 50 and 1000 msec. Display of the images was followed by a random noise mask. Half of the images were presented in colour; half in black \& white. The luminance component of the images remained constant. In the subsequent query phase the same 48 images were intermixed with 48 new images, and the subjects had to indicate which one of the images they had already seen in the presentation phase. We found a significant effect of exposure duration and colour on recognition performance. Subjects performed 5-10\% better for the coloured than for the black \& white images at all exposure durations, even the shortest ones. Surprisingly, performance was not impaired for a comparison group of 31 dichromats (17 protanopes and 14 deuteranopes), who were also better for colour images. The high speed of colour processing indicates that its usefulness might lie in fast image segmentation. Colour-deficient observers seem to be able to compensate their reduced chromatic information range when viewing and analysing complex scenes.},
department = {Department B{\"u}lthoff},
talk_type = {Abstract Talk},
institute = {Biologische Kybernetik},
organization = {Max-Planck-Gesellschaft},
event_place = {T{\"u}bingen, Germany},
event_name = {18th European Conference on Visual Perception},
author = {Gegenfurtner, KR and Wichmann, FA and Sharpe, LT}
}