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@Book { 1870,
   title = {Form, Space and Object: Geometrical Transformations in Object Recognition and Categorization},
   year = {2002},
   pages = {285},
   abstract = {In order to recognize an object, the visual system has to solve two basic problems: The first one is how to recognize an object after spatial transformations, i.e. regardless of its orientation, size and position. The second problem refers to the question how we perceive and categorize different objects as members of the same category.
A central hypothesis in this book is that both problems have a similar structure, and can be conceptualized within an integrative transformational account, based on concepts from geometry: Recognition after spatial transformations, on one hand, relies on Euclidean transformation processes that are conceptualized as frame transformations (or coordinate transformations). Categorization up to the basic level, on the other hand, can be accounted for by non-Euclidean topological (i.e. potentially space-curving) transformations. Thus, an integrative theory of recognition and categorization is suggested, based on a process-based interpretation of Felix Klein’s Erlanger Program.},
   note = {Zugl.: M{\"u}nchen, Univ. , Diss., 2002},
   department = {Department B{\"u}lthoff},
   web_url = {http://www.wvberlin.de/data/inhalt/graf.htm},
   publisher = {WVB},
   address = {Berlin, Germany},
   institute = {Biologische Kybernetik},
   organization = {Max-Planck-Gesellschaft},
   language = {en},
   ISBN = {3-932089-91-X},
   author = {Graf, M}
}

@Article { 6555,
   title = {Transformation Direction Influences Shape-Similarity Judgments},
   journal = {Psychological Science},
   year = {2010},
   month = {4},
   volume = {20},
   number = {4},
   pages = {447-454},
   abstract = {Three experiments provide evidence that the
perceived similarity between two images is systematically
affected by the inherent direction of a transformation that
links the two. Participants were shown short animations
morphing one object into another from the same basic
category. They were then asked to make directional similarity
judgments (‘‘How similar is object A to object B?’’)
for two stationary images drawn from the morph continuum.
Across three experiments, similarity ratings for
identical comparisons were higher when the reference
object, B, had appeared before the comparison object, A,
in the preceding morph sequence. This response to dynamic
transformational sequences is in accordance with
the view that similarity depends on the ease of transformation
between object representations and that transformations
between objects in categorization and object
recognition are psychologically real.},
   department = {Department B{\"u}lthoff},
   web_url = {http://pss.sagepub.com/content/20/4/447.full.pdf+html},
   institute = {Biologische Kybernetik},
   organization = {Max-Planck-Gesellschaft},
   language = {en},
   DOI = {10.1111/j.1467-9280.2009.02310.x},
   author = {Hahn, U and Close, J and Graf, M}
}

@Article { 6240,
   title = {Action observation can prime visual object recognition},
   journal = {Experimental Brain Research},
   year = {2010},
   month = {1},
   volume = {200},
   number = {3-4},
   pages = {251-258},
   abstract = {Observing an action activates action representations in the motor system. Moreover, the representations of manipulable objects are closely linked to the motor systems at a functional and neuroanatomical level. Here, we investigated whether action observation can facilitate object recognition using an action priming paradigm. As prime stimuli we presented short video movies showing hands performing an action in interaction with an object (where the object itself was always removed from the video). The prime movie was followed by a (briefly presented) target object affording motor interactions that are either similar (congruent condition) or dissimilar (incongruent condition) to the prime action. Participants had to decide whether an object name shown after the target picture corresponds with the picture or not (picture–word matching task). We found superior accuracy for prime–target pairs with congruent as compared to incongruent actions across two experiments. Thus, action observation can facilitate recogni
tion of a manipulable object typically involving a similar action. This action priming effect supports the notion that action representations play a functional role in object recognition.},
   department = {Department B{\"u}lthoff},
   department2 = {Research Group Ernst},
   web_url = {http://springerlink.metapress.com/content/a5ph883317156381/fulltext.pdf},
   institute = {Biologische Kybernetik},
   organization = {Max-Planck-Gesellschaft},
   language = {en},
   DOI = {10.1007/s00221-009-1953-8},
   author = {Helbig, HB and Steinwender, J and Graf, M and Kiefer, M}
}

@Article { 4326,
   title = {Predicting point-light actions in real-time},
   journal = {NeuroImage},
   year = {2007},
   month = {5},
   volume = {36},
   number = {Supplement 2},
   pages = {T22-T32},
   abstract = {There is convincing evidence for a mirror system in humans which simulates actions of conspecifics. One possible purpose of such a simulation system is to support action prediction in real-time. Our goal was to study whether the prediction of actions involves a real-time simulation process. We motion-captured a number of human actions and rendered them as previous termpoint-lightnext term action sequences. Observers perceived brief videos of these actions, followed by an occluder and a static test posture. We independently varied the occluder time and the movement gap (i.e., the time between the endpoint of the action and the test posture). Observers were required to judge whether the test stimulus depicted a continuation of the action in the same depth orientation. Prediction performance was best when occluder time and movement gap corresponded, i.e., when the test posture was a continuation of the sequence that matched the occluder duration (Experiments 1, 2 and 4). This pattern of results was destroyed when the sequences and test images were flipped around the horizontal axis (Experiment 3). Overall, our findings suggest that action prediction involves a simulation process that operates in real-time. This process can break down when the actions are presented under viewing conditions for which observers have little experience.},
   web_url = {http://www.sciencedirect.com/science?_ob=MImg\&_imagekey=B6WNP-4NC38V3-5-1\&_cdi=6968\&_user=29041\&_orig=search\&_coverDate=12\%2F31\%2F2007\&_sk=999639999.8997\&view=c\&wchp=dGLbVzz-zSkWz\&md5=94c254feab3c9dfc6fb2b6d7b0ffcd4c\&ie=/sdarticle.pdf},
   institute = {Biologische Kybernetik},
   organization = {Max-Planck-Gesellschaft},
   language = {en},
   DOI = {10.1016/j.neuroimage.2007.03.017},
   author = {Graf, M and Reitzner, B and Corves, C and Casile, A and Giese, M and Prinz, W}
}

@Article { 4769,
   title = {Close coordination between recognition and action: Really two separate streams?},
   journal = {Behavioral and Brain Sciences},
   year = {2007},
   month = {4},
   volume = {30},
   number = {2},
   pages = {210-211},
   abstract = {Somewhat in contrast to their proposal of two separate somatosensory streams, Dijkerman \& de Haan (D\&dH) propose that tactile recognition involves active manual exploration, and therefore involves parietal cortex. I argue that interactions from perception for action to object recognition can be found also in vision. Furthermore, there is evidence that perception for action and perception for recognition rely on similar processing principles.},
   department = {Department B{\"u}lthoff},
   web_url = {http://journals.cambridge.org/action/displayFulltext?type=6\&fid=1306160\&jid=BBS\&volumeId=30\&issueId=02\&aid=1306152\&fulltextType=RA\&fileId=S0140525X07001495},
   institute = {Biologische Kybernetik},
   organization = {Max-Planck-Gesellschaft},
   language = {en},
   DOI = {10.1017/S0140525X07001495},
   author = {Graf, M}
}

@Article { 2284,
   title = {Coordinate Transformations in Object Recognition},
   journal = {Psychological Bulletin},
   year = {2006},
   month = {11},
   volume = {132},
   number = {6},
   pages = {920-945},
   abstract = {A basic problem of visual perception is how we recognize objects after spatial transformations. Three central classes of findings have to be accounted for: (1) Recognition performance varies systematically with orientation, size, and position. (2) Recognition latencies are sequentially additive, suggesting analog transformation processes. (3) Orientation and size congruency effects indicate that recognition involves the adjustment of a perceptual coordinate system. While existing models of object recognition are unable to account for all three types of findings, the data can be explained by a transformational model of recognition (TMR), which relies on coordinate transformations and multiple representations. Recognition is achieved by transforming a generic perceptual coordinate system that defines the correspondence between positions specified in memory and positions in the current visual field so that memory and input representations are aligned. TMR is an analog model of recognition, based on analog (image
-like) representations and analog transformation processes. TMR is compatible with models in computational neuroscience proposing that object recognition involves coordinate transformations, implemented by neural gain (amplitude) modulation. These gain modulation processes correspond to transformations of receptive fields in upstream cortical areas. Coordinate transformations seem to underlie both object recognition and visuomotor control, and may be regarded as a general processing principle of the visual cortex. TMR discriminates between compensation processes in object recognition and mental imagery; coordinate transformations in recognition are more closely related to visuomotor control than to mental rotation. This framework has several advantages and overcomes arguments that were raised against alignment models of recognition.},
   url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/psych-bull-2006-920_2284[0].pdf},
   department = {Department B{\"u}lthoff},
   institute = {Biologische Kybernetik},
   organization = {Max-Planck-Gesellschaft},
   language = {en},
   DOI = {10.1037/0033-2909.132.6.920},
   author = {Graf, M}
}

@Article { 3345,
   title = {The role of action representations in visual object recognition},
   journal = {Experimental Brain Research},
   year = {2006},
   month = {4},
   volume = {174},
   number = {2},
   pages = {221-228},
   abstract = {It is typically assumed that perception for action and object recognition are subserved by functionally and neuroanatomically distinct processing streams in the brain. However, recent evidence challenges this classical view and suggests an interaction between both visual processing streams. While previous studies showed an influence of object perception on action-related tasks, we investigated whether action representations facilitate visual object recognition. In order to address this question, two briefly displayed masked objects were sequentially presented, either affording congruent or incongruent motor interactions. We found superior naming accuracy for object pairs with congruent as compared to incongruent motor interactions (Experiment 1). This action priming effect indicates that action representations can facilitate object recognition. We further investigated the nature of the representations underlying this action priming effect. The effect was absent when the prime stimulus was presented as a word
(Experiment 2). Thus, the action priming effect seems to rely on action representations specified by visual object information. Our findings suggest that processes of object-directed action influence object recognition.},
   url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/HelbigGrafKiefer_2006_EBR_3345[0].pdf},
   department = {Department B{\"u}lthoff},
   web_url = {http://springerlink.metapress.com/content/u22g7hg2r856k062/fulltext.pdf},
   institute = {Biologische Kybernetik},
   organization = {Max-Planck-Gesellschaft},
   language = {en},
   DOI = {10.1007/s00221-006-0443-5},
   author = {Helbig, HB and Graf, M and Kiefer, M}
}

@Article { 2543,
   title = {Orientation congruency effects for familiar objects: Coordinate transformations in object recognition},
   journal = {Psychological Science},
   year = {2005},
   month = {3},
   volume = {16},
   number = {3},
   pages = {214-221},
   abstract = {How do we recognize objects after spatial transformations? Recent neurocomputational models proposed that object recognition is based on coordinate transformations which align memory and stimulus representations. If the recognition of disoriented objects is achieved by adjusting a coordinate system (or reference frame) then recognition should be facilitated when the object is preceded by a different object in the same orientation. Two objects were presented in close temporal contiguity in brief masked displays, either in congruent or incongruent picture plane orientations. In two experiments, naming accuracy was higher for congruent orientations. The congruency effect was independent of superordinate category membership (Experiment 1), and was found for objects with different (horizontal or vertical) main axis of elongation (Experiment 2). The results indicate congruency effects for common familiar objects, even for dissimilar shapes. The findings are compatible with models in which object recognition is achi
eved by an adjustment of a perceptual coordinate system.},
   department = {Department B{\"u}lthoff},
   web_url = {http://www.blackwell-synergy.com/doi/pdf/10.1111/j.0956-7976.2005.00806.x},
   institute = {Biologische Kybernetik},
   organization = {Max-Planck-Gesellschaft},
   language = {en},
   DOI = {10.1111/j.0956-7976.2005.00806.x},
   author = {Graf, M and Kaping, D and B{\"u}lthoff, HH}
}

@Article { 1328,
   title = {Structural descriptions in HIT: a problematic commitment},
   journal = {Behavioral and Brain Sciences},
   year = {2001},
   month = {11},
   volume = {24},
   number = {3},
   pages = {483-484},
   web_url = {http://journals.cambridge.org/action/displayFulltext?type=1\&pdftype=1\&fid=88734\&jid=BBS\&volumeId=24\&issueId=\&aid=88733},
   institute = {Biologische Kybernetik},
   organization = {Max-Planck-Gesellschaft},
   language = {en},
   author = {Graf, M and Schneider, WX}
}

@Article { 1331,
   title = {Komplexes Lernen in der kaufm{\"a}nnischen Erstausbildung: Kognitive und motivationale Aspekte},
   journal = {Zeitschrift f{\"u}r Berufs  und Wirtschaftsp{\"a}dagogik},
   year = {1996},
   volume = {Beiheft 13},
   pages = {23-36},
   institute = {Biologische Kybernetik},
   organization = {Max-Planck-Gesellschaft},
   author = {Stark, R and Gruber, H and Graf, M and Renkl, A and Mandl, H}
}

@Article { 1330,
   title = {F{\"o}rderung von Handlungskompetenz durch geleitetes Probleml{\"o}sen und multiple Lernkontexte},
   journal = {Zeitschrift f{\"u}r Entwicklungspsychologie und P{\"a}dagogische Psychologie},
   year = {1995},
   volume = {27},
   pages = {289-312},
   institute = {Biologische Kybernetik},
   organization = {Max-Planck-Gesellschaft},
   author = {Stark, R and Graf, M and Renkl, A and Gruber, H and Mandl, H}
}

@Inproceedings { 2728,
   title = {On categorization in human and machine},
   journal = {Digital imaging in media and education. 28th workshop of the Austrian Association for pattern recognition (OAGM/AAPR)},
   year = {2004},
   month = {6},
   pages = {245-252},
   department = {Department B{\"u}lthoff},
   editor = {Burger, W. , J. Scharinger},
   publisher = {{\"O}sterreichische Computer Gesellschaft},
   address = {Wien, Austria},
   booktitle = {Digital Imaging in Media and Education},
   institute = {Biologische Kybernetik},
   organization = {Max-Planck-Gesellschaft},
   event_place = {Hagenberg, Austria},
   event_name = {28th Workshop of the Austrian Association for Pattern Recognition (OAGM/AAPR)},
   ISBN = {3-85403-179-3},
   author = {Skokaj, D and Graf, M and Dahl, C and Leonardis, A}
}

@Inproceedings { 2230,
   title = {Object Shape in Basic Level Categorisation},
   year = {2003},
   month = {9},
   pages = {390},
   url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/pdf2230.pdf},
   department = {Department B{\"u}lthoff},
   editor = {Schmalhofer, F. , R. Young, G. Katz},
   publisher = {Erlbaum},
   address = {Mahwah, NJ, USA},
   booktitle = {EuroCogSci 03},
   institute = {Biologische Kybernetik},
   organization = {Max-Planck-Gesellschaft},
   event_place = {Osnabr{\"u}ck, Germany},
   event_name = {European Cognitive Science Conference 2003},
   ISBN = {0-8058-5005-8},
   author = {Graf, M and B{\"u}lthoff, HH}
}

@Inbook { 4491,
   title = {Motor Involvement in Action and Object Perception: Similarity and Complementarity},
   year = {2010},
   month = {11},
   pages = {27-52},
   department = {Department B{\"u}lthoff},
   web_url = {http://www.psypress.com/grounding-sociality-9781848728998},
   editor = {Semin, G. R. , G. Echterhoff},
   publisher = {Psychology Press},
   address = {New York, NY, USA},
   booktitle = {Grounding sociality: neurons, mind, and culture},
   institute = {Biologische Kybernetik},
   organization = {Max-Planck-Gesellschaft},
   language = {en},
   ISBN = {978-1-84872-899-8},
   author = {Graf, M and Sch{\"u}tz-Bosbach, S and Prinz, W}
}

@Inbook { 4492,
   title = {Categorization and Object Shape},
   year = {2010},
   pages = {73-101},
   abstract = {Categorization is essential for perception and provides an important foundation for higher cognitive functions. In this review, I focus on perceptual aspects of categorization, especially related to object shape. In order to visually categorize an object, the visual system has to solve two basic problems. The first one is how to recognize objects after spatial transformations like rotations and size-scalings. The second problem is how to categorize objects with different shapes as members of the same category. I review the literature related to these two problems against the background of the hierarchy of transformation groups specified in Felix Klein’s Erlanger Programm. The Erlanger Programm provides a general framework for the understanding of object shape, and may allow integrating object recognition and categorization literatures.},
   department = {Department B{\"u}lthoff},
   web_url = {http://www.springerlink.com/content/m543xj3618683ml0/},
   editor = {Glatzeder, B. M. , V. Goel, A. M{\"u}ller},
   publisher = {Springer},
   address = {Berlin, Germany},
   series = {Parmenides book series on thinking},
   booktitle = {Towards a theory of thinking: building blocks for a conceptual framework},
   institute = {Biologische Kybernetik},
   organization = {Max-Planck-Gesellschaft},
   language = {en},
   ISBN = {978-3-642-03129-8},
   DOI = {10.1007/978-3-642-03129-8_6},
   author = {Graf, M}
}

@Techreport { 4782,
   title = {Psychophysical results from experiments on recognition \& categorisation},
   year = {2002},
   month = {11},
   number = {IST-2000-29375},
   abstract = {A firm understanding of how the human visual system recognises and categorises objects is important in order to build a successful cognitive vision system. We have reviewed the relevant literature both on visual object recognition and categorisation (chapter 1). Based
on this review and the technical annex of this project we have addressed several topics in a series of psychophysical experiments, focusing on structural aspects of recognition
memory, object similarity in the context of categorisation, shape transformations in categorisation, the role of context in recognition and categorisation, and the interplay
between object motion and shape for categorisation decisions (chapter 2). Based on our psychophysical results we present our view on recognition and categorisation, proposing an integrative framework that serves as a theoretical basis for a computational recognition
system grounded in cognitive research (chapter 3).},
   url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/GraSchWalBul2002_[0].pdf},
   department = {Department B{\"u}lthoff},
   web_url = {http://fhweb.imvs.ch/ppt/content/pub/psychophysical-results-from-experiments-on-recognition-categorisation},
   institute = {Biologische Kybernetik},
   organization = {Max-Planck-Gesellschaft},
   institution = {Fachhochschule Nordwestschweiz, Information Society Technologies Programme, Cognitive Vision Systems},
   language = {en},
   author = {Graf, M and Schwaninger, A and Wallraven, C and B{\"u}lthoff, HH}
}

@Poster { 4606,
   title = {When action influences object perception: Evidence for rapid access to action representations during visual object recognition},
   year = {2007},
   month = {4},
   abstract = {Brain areas involved in action representation (premotor cortex, posterior parietal cortex) are activated when subjects name pictures of manipulable objects, like tools (e.g., Chao \& Martin, 2000). Moreover, behavioral evidence indicates that manipulable objects potentiate possible actions (e.g., Tucker \& Ellis, 1998). Here we investigated whether action representations facilitate object recognition.
Subjects were sequentially presented with two pictures of artifactual manipulable objects (e.g., tools, musical instruments) and were required to name the objects. In the congruent condition both objects afford similar actions, while affordances are dissimilar in the incongruent condition. Stimulus pairs in both conditions were matched for baseline naming accuracy, word frequency, word length, and for visual and semantic similarity.
Naming accuracy was significantly higher in the congruent condition. This action priming effect substantiates our hypothesis that action representations play an important role in the recognition of artifactual manipulable objects.
We further conducted an event-related potentials (ERPs) experiment using the same task and stimuli to determine the temporal and spatial pattern of brain activity underlying the action priming.
An effect of action congruency on ERPs started at about 100ms after the onset of the target object at fronto-central electrodes close to the motor cortex. This finding demonstrates that the action priming effect in object recognition arises from rapid access to action representations in motor areas even though subjects did not act upon the objects.
Altogether, the results suggest that motor knowledge about potential interactions with objects can influence object recognition within the first 100ms of perceptual processing.},
   department = {Department B{\"u}lthoff},
   web_url = {http://www.cimec.unitn.it/events/caos/07/poster_session.htm},
   institute = {Biologische Kybernetik},
   organization = {Max-Planck-Gesellschaft},
   event_place = {Rovereto, Italy},
   event_name = {Rovereto Workshop on Concepts, Actions and Objects (CAOs 2007)},
   language = {en},
   author = {Helbig, HB and Graf, M and Sim, E-J and Kiefer, M}
}

@Poster { 4419,
   title = {Predicting point-light actions in real-time},
   journal = {Journal of Vision},
   year = {2006},
   month = {6},
   volume = {6},
   number = {6},
   pages = {793},
   abstract = {Evidence has accumulated for a mirror system in humans which simulates actions of conspecifics (Wilson \& Knoblich, 2005). One likely purpose of such a simulation system is to support action prediction. We focused on the time-course of action prediction, investigating whether the prediction of actions involves a real-time simulation process.
We motion-captured a number of human actions and rendered them as point light action sequences. In the experiments, we presented brief videos of human actions, followed by an occluder and a static test stimulus. Both the occluder duration (SOA of 100, 400, or 700 ms) and the distance of the test stimulus to the endpoint of the action sequence (corresponding to 100, 400, or 700 ms) were varied independently. Subjects had to judge whether the test stimulus depicted a continuation of the action in the same orientation, or whether the test stimulus was presented in a different orientation in depth as the previous action sequence.
Prediction accuracy was best when SOA and distance to the endpoint corresponded, i.e. when the test image was a continuation of the sequence that matched the occluder duration. This pattern of results was destroyed when the sequences and test images were inverted (flipped around the horizontal axis). In this case, performance simply deteriorated with increasing distance to the end of the sequence. Overall, our findings suggest that action prediction involves a real-time simulation process. This process can break down when the actions are presented under viewing conditions for which we have little experience.},
   department = {Department B{\"u}lthoff},
   web_url = {http://www.journalofvision.org/6/6/793/},
   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 = {10.1167/6.6.793},
   author = {Graf, M and Reitzner, B and Giese, M and Casile, A and Prinz, W}
}

@Poster { 3239,
   title = {Motor Representations in Visual Object Recognition},
   year = {2005},
   month = {2},
   volume = {8},
   pages = {126},
   abstract = {It has been proposed recently that object recognition relies on coordinate transformations, i.e.
on similar processes as visuomotor control [1]. Thus, the two visual streams involved in object
recognition and object-directed action may rely on common computational principles, which
provides the possibility for interactions between the two streams. Existing behavioral and neurophysiological
findings suggest that viewing manipulable objects automatically potentiates
possible actions [e.g., 2,3]. We investigated whether action knowledge has a functional role
in visual object recognition. More specifically, we used a priming paradigm to test whether
objects are recognized better when viewed after another object which affords congruent as
compared to incongruent motor interactions. Two grey-scale pictures of artifactual manipulable
objects were presented sequentially (tools, kitchen utensils, musical instruments). Subjects
were required to name the objects. The stimuli were briefly presented and masked. The presentation
time of the second object was adjusted individually in an adjustment phase so that
naming accuracy approached 80\%. In the congruent condition both objects afforded a similar
motor interaction, and dissimilar motor interactions in the incongruent condition. Stimulus
pairs in both conditions were matched for baseline naming accuracy, word frequency, word
length, as well as visual and semantic similarity. We found that naming accuracy was higher
in the congruent than in the incongruent condition (Experiment 1 and 2). This action congruency
effect indicates that object naming is facilitated by a previous activation of an appropriate
action representation. In two further experiments we investigated the nature of the representations
underlying the action congruency effect. The effect was reduced or absent when the
prime stimulus was inverted (Experiment 3), and when the prime was presented as a word (Experiment
4). This suggests that the action representations underlying this congruency effect
are closer to specific (parameterised) motor representations than to abstract semantic representations.
Overall, the findings suggest that the recognition of manipulable objects involves not
only visual but also action representations. These are not abstract semantic representations, but
are relatively close to motor representations.},
   department = {Department B{\"u}lthoff},
   web_url = {http://www.twk.tuebingen.mpg.de/twk05/programm.php},
   institute = {Biologische Kybernetik},
   organization = {Max-Planck-Gesellschaft},
   event_place = {T{\"u}bingen, Germany},
   event_name = {8th T{\"u}bingen Perception Conference (TWK 2005)},
   author = {Graf, M and Helbig, HB and Kiefer, M}
}

@Poster { 2620,
   title = {Basic level categorization and shape processing: an fMRI study},
   journal = {Journal of Vision},
   year = {2004},
   month = {8},
   volume = {4},
   number = {8},
   pages = {511},
   abstract = {How is basic level categorization achieved in the human brain? Behavioral studies showed that categorization performance depends systematically on the amount of morph transformation (e.g. Graf, 2002). These results may be due to time-consuming compensation processes (deformable template matching). If deforming (i.e. spatial) compensation processes are involved, then categorization might not only comprise the ventral visual pathway, as generally assumed, but also the dorsal stream. Objects from 25 common basic level categories were generated by morphing between two category members (using 3ds max). In the categorization task, subjects had to decide as fast as possible whether two sequentially presented objects belonged to the same category. The morph distance between category members was varied (event-related design). In a second task, the same observers perceived intact morphing sequences, scrambled sequences, and static presentations of different morphs (block design). In the categorization task, response latencies increased with increasing morph distance between exemplars. Correspondingly, the BOLD signal increased with increasing morph distance in the lateral occipital complex, the superior parietal and the frontal cortices. Control analyses showed that this pattern of activation cannot be reduced to task difficulty, or increasing shape dissimilarity. In the second task we found parietal activation for the contrast between intact vs. scrambled morphing sequences which was close to the dorsal activation in the categorization task, but not identical. The results suggest that basic level categorization relies on a network of ventral, dorsal and frontal areas. The activation within this network depends systematically on the amount of shape transformation. The dorsal activation seems related to compensation processes in parietal cortex, i.e. spatial (deforming) transformation processes. These findings are in accordance with an alignment approach of categorization.},
   department = {Department B{\"u}lthoff},
   web_url = {http://www.journalofvision.org/content/4/8/511.abstract},
   institute = {Biologische Kybernetik},
   organization = {Max-Planck-Gesellschaft},
   event_place = {Sarasota, FL, USA},
   event_name = {Fourth Annual Meeting of the Vision Sciences Society (VSS 2004)},
   DOI = {10.1167/4.8.511},
   author = {Graf, M and Dahl, C and Erb, M and Grodd, W and B{\"u}lthoff, HH}
}

@Poster { 2773,
   title = {The role of action affordances in visual object recognition},
   journal = {Perception},
   year = {2004},
   month = {8},
   volume = {33},
   number = {ECVP Abstract Supplement},
   pages = {75},
   abstract = {Brain areas involved in action representation (pre-motor cortex, posterior parietal cortex) are activated when subjects name pictures of artifactual objects, like tools (eg Chao and Martin, 2000 NeuroImage 12 478 - 484). Moreover, psychophysical evidence indicates that manipulable objects automatically potentiate possible actions (eg Tucker and Ellis, 1998 Journal of Experimental Psychology: Human Perception and Performance 24 830 - 846). We investigated whether knowledge about action affordances is actually involved in object recognition. We examined with a priming paradigm whether objects with congruent affordances are named more accurately than objects with incongruent affordances. Two gray-scale pictures of artifactual manipulable objects were sequentially presented (tools, kitchen utensils, musical instruments). Subjects were required to name the objects. Stimuli were briefly presented and masked. The presentation time of the second object was adjusted individually in an adjustment phase so that accuracy approached 80\%. In the congruent condition, both objects afford the same action (eg 'twisting', 'pouring'), while the affordances differ in the incongruent condition. Stimulus pairs in both conditions were matched for baseline accuracy, word frequency, word length, as well as visual and semantic similarity. Naming accuracy was significantly higher in the congruent condition. These findings substantiate our hypothesis that action affordances play an important role in the identification of artifactual manipulable objects.},
   url = {http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/pdf2773.pdf},
   department = {Department B{\"u}lthoff},
   web_url = {http://www.perceptionweb.com/abstract.cgi?id=v040364},
   institute = {Biologische Kybernetik},
   organization = {Max-Planck-Gesellschaft},
   event_place = {Budapest, Hungary},
   event_name = {27th European Conference on Visual Perception},
   author = {Helbig, HB and Graf, M and Kiefer, M}
}

@Poster { 2619,
   title = {Categorization and Object Shape: Behavioral Data and Global fMRI Analysis},
   journal = {NeuroImage},
   year = {2004},
   month = {6},
   volume = {22},
   number = {Supplement 1},
   pages = {e946-e947},
   abstract = {How is basic level categorization achieved in the human brain? Deforming shape (morphing) transformations are
well suited to describe the shape variability of members of common basic level categories (Figure 1). Behavioral
experiments showed that categorization performance deteriorates systematically with increasing amount of morph
transformation (Dahl, Graf, and B{\"u}lthoff, 2003; Graf, 2002). A possible explanation for these findings is that
categorization relies on time-consuming compensation processes (deformable template matching). We tested,
using fMRI, whether spatial (deforming) compensation processes are involved in categorization, and
hypothesized that such processes would additionally activate the dorsal stream.
Objects from 25 common basic level categories were generated by morphing between two members of the same
category (using 3ds max). Subjects were familiarized with all objects before the experiment. Eleven subjects
participated in two tasks, starting with the categorization task. Subjects had to decide as fast as possible whether
two sequentially presented objects belonged to the same basic level category. The transformational distance
between category members was varied (event-related design). In a second task, the same observers perceived
intact morphing sequences, scrambled morphing sequences, and static presentations of different morph exemplars
(updating task, block design). fMRI data were acquired on a 3T scanner (Siemens Trio), with 24 slices of 64x64
voxels every two seconds (resolution of 3x3x5 mm3), and whole brain coverage.
Behaviorally, we found that in the categorization task, the response latencies for same trials increased with
increasing morph distance between two category members. Correspondingly, the fMRI analysis, contrasting long
vs. short morph distance, revealed an increasing BOLD signal in LOC (lateral occipital complex) in both
hemispheres. Moreover, we found activation in the superior parietal cortices (BA 7) and in the right frontal cortex
(BA 44) (Figure 2). Control analyses showed that this pattern of activation cannot be reduced to task difficulty, or
increasing dissimilarity between the objects. In the second task we found dorsal activation for the comparison
between intact vs. scrambled morphing sequences (and additional bilateral activation in LOC when intact
morphing sequences were compared to scrambled and static sequences). The parietal activation, which was
located close to the dorsal activation in the categorization task (Figure 3), seems related to the perception of
continuously morphing objects.
These results suggest that basic level categorization is not limited to the ventral pathway, but rather relies on a
network of ventral, dorsal and frontal activation. The activation within this network systematically depends on the
amount of shape transformation. The dorsal activation seems related to compensational processes taking place in
parietal cortex, i.e. spatial (deforming) transformation processes. These findings are in accordance with an
alignment approach of object recognition and categorization.},
   department = {Department B{\"u}lthoff},
   web_url = {http://www.sciencedirect.com/science/article/pii/S1053811905700161},
   institute = {Biologische Kybernetik},
   organization = {Max-Planck-Gesellschaft},
   event_place = {Budapest, Hungary},
   event_name = {10th Annual Meeting of the Organization for Human Brain Mapping (HBM 2004)},
   DOI = {10.1016/S1053-8119(05)70016-1},
   author = {Dahl, C and Graf, M and Erb, M and Grodd, W and B{\"u}lthoff, HH}
}

@Poster { 2679,
   title = {Form and Space in Perception and Art},
   year = {2004},
   month = {6},
   department = {Department B{\"u}lthoff},
   institute = {Biologische Kybernetik},
   organization = {Max-Planck-Gesellschaft},
   event_place = {Bolzano, Italy},
   event_name = {The Depictive Space of Perception: A Conference on Visual Thought},
   author = {Graf, M}
}

@Poster { 2621,
   title = {Visual Categorization and Object Shape: ROI Analysis of fMRI Data},
   journal = {NeuroImage},
   year = {2004},
   month = {6},
   volume = {22},
   number = {Supplement 1},
   pages = {e956-e958},
   abstract = {Introduction:
Visual categorization is a fundamental capability of the visual system. Deforming shape (morphing)
transformations are well suited to describe the shape variability of members of common basic level categories
(see Figure 1). We investigated the cortical processes underlying basic level categorization, using region of
interest (ROI) analyses.
Material and Methods:
Objects from 25 common basic level categories were generated by morphing between two members of the same
category. Eleven subjects participated in three tasks, starting with the categorization task. Subjects had to decide
as fast as possible whether two sequentially presented objects belonged to the same basic level category. The
transformational distance between category members was varied (event-related design). In a second task, the
updating task, the same observers perceived intact morphing sequences, scrambled morphing sequences, and
static presentations of different morph exemplars (block design). In a third task [1] we presented intact objects,
scrambled objects, or periods of simple fixation. Subjects were required to perform a one-back-task (shape task,
block design).
fMRI data were acquired on a 3T scanner (Siemens Trio), measuring 24 slices of 64x64 voxels every two seconds
(resolution of 3x3x5 mm3 ), covering the whole brain.
Based on the shape processing tasks (red in Figure 2), we calculated ROIs. While the contrast ’intact objects -
scrambled objects’ revealed the usual LOC region (Figure 2c), a large network of ventral, dorsal and frontal
regions was activated when also the fixation period was included (contrast ’intact - scrambled - fixation’) (Figure
2a,b,d). We used these ventral, dorsal and frontal regions as templates for ROI analysis.
Within these ROIs, averaged time courses were calculated using the tools of Kalina Christoff
(http://www-psych.stanford.edu/\verb=~=kalina/SPM99/Tools/roi.html).
Results:
In the categorization task the contrast long vs. short morph distance revealed an increasing BOLD signal in LOC
(lateral occipital complex), in the superior parietal cortex (BA 7), and in the frontal cortex (BA 44) (Figure 2
yellow). ROI analyses showed highly similar pattern of results for ventral and dorsal regions (Figure 3). In the
updating task we found dorsal activation for the contrast between intact - (scrambled + static) conditions. This
activation spot was close to the dorsal activation in the categorization task, but was not identical (Figure 2b
green). Nevertheless, an ROI analysis on the categorization data, based on the dorsal activation in the updating
task as a ROI, showed similar results as the previous analyses.
Discussion:
The results confirm that basic level categorization is not limited to the ventral pathway, but rather relies on a
network of ventral, dorsal and frontal areas. ROI analyses showed that the activation within this network is
systematically dependent on the amount of shape transformation. Similar patterns of activation were found in the
ventral and dorsal stream, suggesting that both visual streams are involved in visual categorization.},
   department = {Department B{\"u}lthoff},
   web_url = {http://www.sciencedirect.com/science/article/pii/S1053811905700161},
   institute = {Biologische Kybernetik},
   organization = {Max-Planck-Gesellschaft},
   event_place = {Budapest, Hungary},
   event_name = {10th Annual Meeting of the Organization for Human Brain Mapping (HBM 2004)},
   DOI = {10.1016/S1053-8119(05)70016-1},
   author = {Erb, M and Graf, M and Dahl, C and Grodd, W and B{\"u}lthoff, HH}
}

@Poster { 2618,
   title = {Shape Processing in Basic Level Categorization—: An fMRI Investigation},
   year = {2004},
   month = {2},
   volume = {7},
   pages = {101},
   abstract = {How is basic level categorization achieved in the human brain? Deforming shape (morphing)
transformations are well suited to describe the shape variability of members of common basic
level categories. Behavioral experiments showed that categorization performance deteriorates
systematically with increasing amount of morph transformation [1, 2]. A possible explanation
for these ndings is that categorization relies on time-consuming compensation processes
(deformable template matching). If spatial compensation processes are involved, then categorization
might not only comprise the ventral visual pathway, as generally assumed, but also the
dorsal stream. We investigated this question with functional MRI.
Objects from 25 common basic level categories were generated by morphing between two
members of the same category (using 3ds max). Eleven subjects participated in two tasks,
starting with the categorization task. Subjects had to decide as fast as possible whether two
sequentially presented objects belonged to the same basic level category. The transformational
distance between category members was varied (event-related design). In a second task,
the same observers perceived intact morphing sequences, scrambled morphing sequences, and
static presentations of different morph exemplars (block design). fMRI data were acquired on a
3T scanner (Siemens Trio), measuring 24 slices of 64x64 voxels every two seconds (resolution
of 3x3x5 mm
A
).
In the categorization task, the response latencies for same trials increased with increasing
morph distance between two category members. Correspondingly, the contrast long vs. short
morph distance revealed an increasing BOLD signal in LOC (lateral occipital complex). Moreover,
activation increased also in the superior parietal cortex (BA 7) and in the frontal cortex
(BA 44). Control analyses showed that this pattern of activation cannot be reduced to task
difculty, or increasing dissimilarity between the objects. In the second task we found dorsal
activation for the comparison between intact vs. scrambled morphing sequences. This activation
spot was close to the dorsal activation in the categorization task, but was not identical.
The results suggest that basic level categorization is not limited to the ventral pathway,
but rather relies on a network of ventral, dorsal and frontal activation. The activation within
this network is systematically dependent on the amount of shape transformation. The dorsal
activation seems related to compensational processes taking place in parietal cortex, i.e. spatial
(deforming) transformation processes. These ndings are in accordance with an alignment
approach of object recognition and categorization.},
   department = {Department B{\"u}lthoff},
   web_url = {http://www.twk.tuebingen.mpg.de/twk04/index.php},
   institute = {Biologische Kybernetik},
   organization = {Max-Planck-Gesellschaft},
   event_place = {T{\"u}bingen, Germany},
   event_name = {7th T{\"u}bingen Perception Conference (TWK 2004)},
   author = {Dahl, C and Graf, M and Erb, M and Kourtzi, Z and Grodd, W and B{\"u}lthoff, HH}
}

@Poster { 2340,
   title = {Reference Frame Adjustment In Object Recognition},
   year = {2003},
   month = {11},
   volume = {44},
   pages = {1},
   abstract = {If the recognition of disoriented common objects relies on an adjustment of a reference frame, then recognition should be facilitated if the object is preceded by a different object in the same orientation. Two objects from different basic categories were presented in close temporal contiguity in brief masked displays, either in the same or in different picture plane orientations. Subjects had to name both objects. Before the test phase, presentation times for the second object were individually adjusted such that accuracy was at 80\%. Line-drawings of common objects were employed. In Experiment 1, objects were selected such that 12 were from biological and 12 from artifact categories. In Experiment 2, 12 objects with a vertical and 12 with a horizontal main axis were used. In both experiments, naming accuracy was higher when the two objects had congruent orientations. This effect was independent of object category, and of the objects’ main axis.},
   department = {Department B{\"u}lthoff},
   web_url = {http://www.psychonomic.org/past-meeting.html},
   institute = {Biologische Kybernetik},
   organization = {Max-Planck-Gesellschaft},
   event_place = {Vancouver, Canada},
   event_name = {44th Annual Meeting of The Psychonomic Society},
   author = {Graf, M and Kaping, D and B{\"u}lthoff, HH}
}

@Poster { 2229,
   title = {Shape transformations and image-plane rotations in object categorization},
   journal = {Journal of Vision},
   year = {2003},
   month = {10},
   volume = {3},
   number = {9},
   pages = {506},
   abstract = {Previous research suggested that the shape variability of objects from the same basic level category can be conceptualized by transformations which continuously change object shape (topological transformations). Experiments with line drawings (2D outline shapes) demonstrated that categorization latencies and error rates increase with increasing amount of shape transformation (Graf, 2001). We investigated whether these results generalize to more realistic gray-level images rendered from 3D object models. We also studied the effects of combined shape transformations and image-plane rotations on categorization performance.

New category members were produced by morphing between objects from the same basic level category. Subjects were required to decide whether two sequentially presented objects belonged to the same basic level category or not. In Experiment 1 the amount of shape transformation was varied, while in Experiment 2 topological distance and image-plane orientation were manipulated.

Categorization performance (latencies and accuracy) deteriorated systematically with increased shape transformation, both for upright (Exp. 1) and for rotated (Exp. 2) objects. Furthermore, Exp. 2 showed that categorization latencies increased with increasing amount of orientation change. There was no interaction between shape transformation and object orientation.

The results confirm that categorization performance is systematically related to the amount of shape transformation, both for line drawings and gray-level images, as well as for upright and plane rotated objects. In addition, orientation dependency was corroborated with a basic level categorization task. Finally, categorization processes which compensate for shape changes and plane rotations seem to be independent, confirming previous evidence of independent effects for other combinations of spatial transformations (e.g. Lawson et al., 2000). The results support an image-based model of basic level categorization.},
   department = {Department B{\"u}lthoff},
   web_url = {http://www.journalofvision.org/content/3/9/506.short},
   institute = {Biologische Kybernetik},
   organization = {Max-Planck-Gesellschaft},
   event_place = {Sarasota, FL, USA},
   event_name = {Third Annual Meeting of the Vision Sciences Society (VSS 2003)},
   DOI = {10.1167/3.9.506},
   author = {Graf, M and B{\"u}lthoff, HH}
}

@Poster { 2417,
   title = {Categorisation performance depends systematically on shape transformations},
   journal = {Perception},
   year = {2003},
   month = {9},
   volume = {32},
   number = {ECVP Abstract Supplement},
   pages = {117},
   abstract = {The shape variability of objects from the same basic-level category can be conceptualised by transformations which continuously change object shape. Morphing between members of a basic-level category allows to systematically vary the shape of common objects. We demonstrated that categorisation performance depends on the amount of shape transformation, using a sequential matching task (Graf and B{\"u}lthoff, 2003, EuroCogSci, Osnabr{\"u}ck, Germany). We further investigated shape dependence of basic-level categorisation with name matching and rating tasks. We created five category members (1\%, 25\%, 50\%, 75\%, and 100\% morphs) for twenty-five basic-level categories, based on morphable 3-D object models. Objects were rendered as grey-level images and presented in a canonical orientation. In the speeded name-matching experiment, subjects had to decide whether an object corresponded to a category name. In a second experiment, subjects were required to rate the typicality of the objects, ie they had to rate how well the objects corresponded to their mental image of the category. Both name-matching latencies and typicality ratings depended systematically on the amount of shape transformation. Name-matching latencies were significantly shorter for exemplars that were more in the middle of the morphing sequence. These exemplars were also rated as more typical in experiment 2. The findings confirm the systematic dependence of categorisation performance on the amount of shape transformation. Shapes that are rated as more prototypical are categorised faster. This shape-dependence in basic-level categorisation is reminiscent of the orientation-dependence in recognition, where the canonical perspective is rated as more typical and recognised faster [Palmer et al, 1981, in Attention and Performance IX Eds J Long, A Baddeley (Hillsdale, NJ: Lawrence Erlbaum Associates) pp 135 - 151]. Overall, the results support an extension of the image-based model of recognition (B{\"u}lthoff et al, 1995 Cerebral Cortex 3 297 - 260) to basic-level categorisation.},
   department = {Department B{\"u}lthoff},
   web_url = {http://www.perceptionweb.com/abstract.cgi?id=v031197},
   institute = {Biologische Kybernetik},
   organization = {Max-Planck-Gesellschaft},
   event_place = {Paris, France},
   event_name = {26th European Conference on Visual Perception},
   author = {Dahl, C and Graf, M and B{\"u}lthoff, HH}
}

@Poster { 2226,
   title = {Orientation congruency effect in object recognition},
   journal = {Perception},
   year = {2003},
   month = {9},
   volume = {32},
   number = {ECVP Abstract Supplement},
   pages = {117},
   abstract = {There is plenty of evidence that object recognition is orientation-dependent, but there is still considerable debate why recognition performance depends on orientation. It was proposed that recognition relies on an adjustment of a perceptual reference frame [Graf, 2002 Form, Space and Object. Geometrical Transformations in Object Recognition and Categorization (Berlin: Wissenschaftlicher Verlag)]--so that the recognition of disoriented objects would be facilitated if it is preceded by a different object in the same orientation. These orientation congruency effects were demonstrated previously for letters (Jolicoeur, 1990 Journal of Experimental Psychology: Human Perception and Performance 16 351 - 364) and for novel objects (Gauthier and Tarr, 1997 Perception 26 51 - 73), but not yet for common objects. Two objects from different categories were presented in close temporal contiguity in brief masked displays, either in the same or in different picture plane orientations. Subjects were required to name the objects. The main dependent measure was the number of errors. Line-drawings of twenty-four common objects were employed. Presentation times for the second object were individually adjusted before the test phase such that accuracy was at 80\%, when using a different set of objects. Naming accuracy was significantly higher when the orientation of the second object was congruent with the orientation of the previously presented object. Thus, an orientation congruency effect could be demonstrated also with common objects from different basic-level categories. The results suggest that the recognition of disoriented objects involves an adjustment of an abstract frame of reference which facilitates the recognition of different objects in the same orientation. This finding provides further important constraints for any model of object recognition.},
   department = {Department B{\"u}lthoff},
   web_url = {http://www.perceptionweb.com/abstract.cgi?id=v031203},
   institute = {Biologische Kybernetik},
   organization = {Max-Planck-Gesellschaft},
   event_place = {Paris, France},
   event_name = {26th European Conference on Visual Perception},
   author = {Graf, M and Kaping, D and B{\"u}lthoff, HH}
}

@Poster { 2321,
   title = {Basic level categorization and object shape},
   year = {2003},
   month = {7},
   department = {Department B{\"u}lthoff},
   web_url = {http://www.unites.uqam.ca/sccog/indexen.html},
   institute = {Biologische Kybernetik},
   organization = {Max-Planck-Gesellschaft},
   event_place = {Montr{\'e}al, Canada},
   event_name = {UQ{\`A}M Summer Institute in Cognitive Sciences 2003 on Categorisation},
   author = {Graf, M and B{\"u}lthoff, HH}
}

@Poster { 2227,
   title = {Form und Orientierung bei der Kategorisierung von Objekten},
   journal = {Experimentelle Psychologie},
   year = {2003},
   month = {3},
   volume = {45},
   pages = {82},
   abstract = {Die Formvariabilit{\"a}t von Objekten einer Basiskategorie kann durch topologische (verformende) Transformationen gut beschrieben werden. Experimente mit Linienzeichnungen zeigten, dass sich die Performanz bei der Kategorisierung systematisch verschlechtert mit zunehmendem Umfang der Formtransformation [Graf, Journal of Vision, 1(3), 98a (2001)]. Wir untersuchten, ob sich diese Befunde generalisieren lassen auf Grauwertbilder (basierend auf 3-D Objektmodellen) und auf in der Bildebene rotierte Objekte.
Neue Kategoriemitglieder wurden erstellt durch Morphen zwischen Objekten der selben Basiskategorie. Zwei Objekte wurden sequentiell pr{\"a}sentiert und die Probanden mussten entscheiden, ob beide der gleichen Kategorie angeh{\"o}ren. 
Reaktionszeiten und Fehlerraten nahmen systematisch zu mit dem Umfang der Formtransformation, sowohl f{\"u}r die Grauwertbilder als auch f{\"u}r in der Bildebene rotierte Objekte. Auch mit dem Umfang der Rotation stiegen die Reaktionszeiten an. Es zeigte sich keine Interaktion zwischen topologischer Transformation und Rotation. 
Die Ergebnisse best{\"a}tigen und erweitern die fr{\"u}heren Befunde. Sie legen ein bildbasiertes Modell der Kategorisierung auf Basisebene nahe.},
   department = {Department B{\"u}lthoff},
   editor = {J. Golz, F. Faul, R. Mausfeld},
   institute = {Biologische Kybernetik},
   organization = {Max-Planck-Gesellschaft},
   event_place = {Kiel, Germany},
   event_name = {45. Tagung Experimentell Arbeitender Psychologen (TeaP 2003)},
   author = {Graf, M and B{\"u}lthoff, HH}
}

@Poster { 2352,
   title = {Analog Shape Transformations in Basic Level Categorization?},
   year = {2003},
   month = {2},
   volume = {6},
   pages = {148},
   abstract = {It has been shown that basic level categorization performance deteriorates systematically
with increasing shape transformation between two sequentially presented objects,
providing evidence for an image-based model of categorization. Furthermore, categorization
latencies were shown to be sequentially additive, which suggests that categorization
relies on analog compensation processes, i.e. on processes which traverse
intermediate points on the transformational path between category representation and
perceived stimulus (Graf, doctoral dissertation, Wissenschaftlicher Verlag Berlin, 2002).
Using a dierent experimental paradigm, we tried to nd converging evidence that categorization
is based on analog shape transformations. Category members from common
object categories were produced by morphing between two objects from the same basic
level category. Subjects were rst familiarized with all category members. In the
experiment, three objects were presented sequentially and subjects were required to
decide whether all three belonged to the same category. The third object was a morph
whose shape was either in between the rst and the second object (INTER), the same
as the second object, or morphed beyond the second object (EXTRA). A signicant
main eect of condition was found. Reaction times for the INTER condition were
faster then for the EXTRA condition. Thus, categorization decisions were faster when
the third object was located on the assumed path of transformation between the rst
two objects. Since all objects were familiar, the advantage for the INTER condition
seems to result from a previous activation of intermediate shapes in the categorization
process, suggesting analog shape transformations in categorization. Other image-based
accounts seem less appropriate, but cannot be excluded at present.},
   department = {Department B{\"u}lthoff},
   web_url = {http://www.twk.tuebingen.mpg.de/twk03/},
   institute = {Biologische Kybernetik},
   organization = {Max-Planck-Gesellschaft},
   event_place = {T{\"u}bingen, Germany},
   event_name = {6. T{\"u}binger Wahrnehmungskonferenz (TWK 2003)},
   author = {Dahl, C and Graf, M and B{\"u}lthoff, HH}
}

@Poster { 2228,
   title = {Categorization and object shape},
   year = {2003},
   month = {2},
   volume = {6},
   pages = {150},
   abstract = {Shape variability of objects from a basic level category usually can be described well
with continuous shape transformations (topological transformations). Previous experiments
with line drawings showed that categorization performance depends systematically
on the amount of shape transformation, both in speeded categorization tasks
and rating tasks (Graf, doctoral dissertation, Wissenschaftlicher Verlag Berlin, 2002).
We investigated whether this systematic dependency can be replicated under dierent
conditions. Gray-level images of new category members were produced by morphing
between members of the same basic level category. Two images were presented sequentially
and subjects were required to decide whether they belonged to the same category.
The amount of shape transformation between members of the same category was varied
systematically. Objects were presented either upright (Experiment 1), in dierent
orientations in the picture plane (Experiment 2) or in dierent equidistant positions
(Experiment 3). In general, categorization performance deteriorated systematically
with increased shape transformation. In Experiment 2, categorization performance depended
both on the amount of shape change and orientation change, while there was no
signicant interaction between orientation and shape. The eect of shape transformation
was found despite position changes (Experiment 3). The systematic dependency of
categorization performance on the amount of shape transformation was replicated with
gray-level images, for upright objects, image-plane rotated, and for translated objects.
This indicates that the systematic dependency on shape changes is not simply due to
low-level processes. Processes which compensate for shape and for orientation changes
seem independent, which is in agreement with previous ndings for other combinations
of transformations. Overall, the ndings strongly support an image-based model of
categorization.},
   department = {Department B{\"u}lthoff},
   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 = {Graf, M and B{\"u}lthoff, HH}
}

@Poster { 2457,
   title = {Geometrical transformations in object categorization},
   journal = {Journal of Vision},
   year = {2002},
   month = {11},
   volume = {2},
   number = {7},
   pages = {691},
   abstract = {A previous speeded categorization experiment demonstrated that basic level categorization performance deteriorates with increasing amount of topological (warping) transformation between two successively presented category members (Graf, VSS 2001). If topological transformations are involved in basic level categorization, then performance in related tasks should also be influenced by the amount of shape deformation. In particular, the typicality (or representativeness) of category members should be determined by the transformational distance to the category representation. Also, shape similarity should decrease with increasing transformational distance between the objects.
These predictions were investigated for 2D outline shapes of objects from 25 common and familiar object categories. In the typicality task, subjects had to rate the typicality of different category members that were produced with a warping algorithm — i.e. had to judge how well the objects fit with their idea of the category. In the similarity task, the amount of topological transformation between two objects from the same basic level category was manipulated, and subjects had to rate the similarity of the objects.
The results confirmed the predictions: First, typicality ratings varied in a systematic way with topological shape transformation: A graded category structure was found, and typicality decreased with increasing distance to the most typical exemplar. Second, perceived similarity decreased in a highly significant way with increasing amount of topological transformation.

These findings indicate that basic level categorization performance and perceived shape similarity depend on the amount of topological transformation. The results can be accounted for by an alignment model of categorization and similarity which involves deforming transformations. The suggested model can be regarded as an image-based extension to the structural alignment account of similarity (e.g. Markman \& Gentner, 1993).},
   department = {Department B{\"u}lthoff},
   web_url = {http://www.journalofvision.org/2/7/691/},
   institute = {Biologische Kybernetik},
   organization = {Max-Planck-Gesellschaft},
   event_place = {Sarasota, FL, USA},
   event_name = {Second Annual Meeting of the Vision Sciences Society (VSS 2002)},
   DOI = {10.1167/2.7.691},
   author = {Graf, M}
}

@Poster { 2225,
   title = {Kategorisierung durch verformende Transformationen?},
   year = {2002},
   month = {9},
   volume = {43},
   abstract = {Verschiedene Mitglieder einer Objektkategorie auf Basisebene (wie z.B. Fisch, Tasse) lassen sich h{\"a}ufig durch relativ einfache verformende Transformationen ineinander {\"u}berf{\"u}hren. Ein fr{\"u}heres Experiment zeigte, dass bei einer Kategorisierungsaufgabe die Reaktionszeit und Fehlerrate mit zunehmendem Umfang der verformenden Transformation ansteigen (Graf, 2001). Es wurde deshalb untersucht, ob die Typizit{\"a}t (Repr{\"a}sentativit{\"a}t) und Form{\"a}hnlichkeit von Kategoriemitgliedern ebenfalls in systematischem Zusammenhang stehen zu verformenden Transformationen.
Mit Hilfe eines Warping-Algorithmus wurden auf Basis von je zwei Mitgliedern einer Kategorie zwischenliegende Exemplare erstellt, und so 2-D Silhouetten f{\"u}r Objekte aus 25 bekannten Objektkategorien erzeugt. In der Typizit{\"a}tsaufgabe mussten die Probanden beurteilen, wie gut die Objekte zu ihrer Vorstellung der Kategorie passen. In der {\"A}hnlichkeitsaufgabe sollte die {\"A}hnlichkeit von je zwei Objekten einer Kategorie beurteilt werden.
Die Ergebnisse best{\"a}tigten die Vorhersagen: Zum einen variierten die Typizit{\"a}tsratings auf systematische Weise mit der Formtransformation; die Typizit{\"a}t nahm mit zunehmender Distanz zum typischsten Kategoriemitglied ab. Zum zweiten verringerte sich die wahrgenommene {\"A}hnlichkeit mit zunehmendem Umfang verformender Transformationen.
Die Befunde demonstrieren, dass die Kategorisierung und Form{\"a}hnlichkeit von Objekten vom Umfang verformender Transformationen abh{\"a}ngen. Die Daten k{\"o}nnen durch ein Alignment-Modell erkl{\"a}rt werden, das verformende Transformationen beinhaltet. Das vorgeschlagene Modell kann als bild-basierte Erweiterung des structural alignment Modells (z.B. Markman, 2001) betrachtet werden.},
   department = {Department B{\"u}lthoff},
   web_url = {http://www.dgps.de/aktivitaeten/kongress/2002/},
   editor = {van der Meer, E.; Hagendorf, H.; Beyer, R.; Kr{\"u}ger, F.; Nuthmann, A.; Schulz, S.},
   institute = {Biologische Kybernetik},
   organization = {Max-Planck-Gesellschaft},
   event_place = {Berlin, Germany},
   event_name = {43. Kongress der Deutschen Gesellschaft f{\"u}r Psychologie},
   author = {Graf, M}
}

@Poster { 1332,
   title = {Typizit{\"a}t und Form{\"a}hnlichkeit von Kategoriemitgliedern sind beeinflusst durch topologische Transformationen},
   year = {2002},
   month = {2},
   volume = {5},
   pages = {82},
   abstract = {Verschiedene Mitglieder einer basic level Kategorie lassen sich h{\"a}ufig durch eine relativ
einfache topologische (verformende) Transformation ineinander {\"u}berf{\"u}hren (sog. Gummituch-
Geometrie). Ein fr{\"u}heres Experiment zeigte, dass bei einer Kategorisierungsaufgabe
unter Zeitdruck die Reaktionszeit und Fehlerrate ansteigen mit zunehmendem
Umfang der topologischen Transformation von zwei sequentiell pr{\"a}sentierten Kategoriemitgliedern
(Graf, TWK 2001). Falls topologische Transformationen bei der basic level
Kategorisierung involviert sind, dann sollte die Performanz in verwandten Aufgaben
ebenfalls durch den Umfang der Formdeformation beeinflusst sein. Zum einen sollte die
Typizit{\"a}t (Repr{\"a}sentativit{\"a}t) der Kategoriemitglieder bestimmt sein durch die transformationale
Distanz zur Kategorierepr{\"a}sentation. Zum anderen sollte die Form{\"a}hnlichkeit
von zwei Objekten abnehmen mit zunehmender topologischer Transformation zwischen
den Objekten.
Diese Vorhersagen wurden untersucht f{\"u}r 2D Silhouetten (outline shapes) von Objekten
aus 25 bekannten Objektkategorien. In der Typizit{\"a}tsaufgabe mussten die Vpn die Typizit{\"a}t
von verschiedenen Kategoriemitgliedern beurteilen, die mit einem Morphing-Algorithmus
erzeugt wurden – d.h. sie sollten beurteilen, wie gut die Objekte zu ihrer Vorstellung
der Kategorie passen. In der {\"A}hnlichkeitsaufgabe wurde der Umfang der
topologischen Transformation zwischen zwei Objekten der gleichen basic level Kategorie
manipuliert, und die Vpn mussten die {\"A}hnlichkeit der Objekte beurteilen.
Die Ergebnisse best{\"a}tigten die Vorhersagen: Zum einen variierten die Typizit{\"a}tsratings
auf systematische Art und Weise mit der topologischen Formtransformation. Die Ratings
zeigten eine Kategoriestruktur, bei der die Typizit{\"a}t abnahm mit zunehmender Distanz
zum typischsten Kategoriemitglied. Zum zweiten nahm die wahrgenommene {\"A}hnlichkeit
ab mit zunehmendem Umfang topologischer Transformation.
Die Befunde demonstrieren, dass die basic level Kategorisierung und die Form{\"a}hnlichkeit
von Objekten vom Umfang topologischer Transformation abh{\"a}ngen. Die Daten k{\"o}nnen
durch ein Alignment-Modell der Kategorisierung und der {\"A}hnlichkeit erkl{\"a}rt werden,
das topologische Transformationen beinhaltet. Das vorgeschlagene Modell kann als
eine bild-basierte Erweiterung des structural alignment Modells der {\"A}hnlichkeit (z.B.
Markman \& Gentner, 1993) betrachtet werden.},
   department = {Department B{\"u}lthoff},
   web_url = {http://www.twk.tuebingen.mpg.de/twk02/},
   institute = {Biologische Kybernetik},
   organization = {Max-Planck-Gesellschaft},
   event_place = {T{\"u}bingen, Germany},
   event_name = {5. T{\"u}binger Wahrnehmungskonferenz (TWK 2002)},
   author = {Graf, M}
}

@Poster { 1334,
   title = {Analog topological transformations in basic level object recognition},
   journal = {Journal of Vision},
   year = {2001},
   month = {12},
   volume = {1},
   number = {3},
   pages = {98},
   abstract = {Purpose: Several studies suggest that the image-based approach to object recognition can be extended to basic level recognition, but it is not clear yet how basic level recognition is achieved. It seems that the shapes of category members on the basic level can be aligned by rather simple topological (warping) transformations — for most biological and many artifact categories. This study was motivated by the hypothesis that basic level recognition involves analog topological transformation processes — in order to achieve an alignment of stimulus representation and object representation. Two research questions were investigated: (1) Does categorization performance depend on the amount of topological transformation? (2) If systematic effects can be detected, are these effects caused by analog transformation processes? Methods: Images from 16 biological and 14 artifact categories were scanned. On the basis of two members of a category, with morphing software new exemplars were produced as intermediate morphs at specific transformational distances. In every trial two backward masked images were presented sequentially (sequential matching task). The transformational distance between the two images was varied. Subjects had to decide by key press whether both images belonged to the same basic level category or not. Results: The predictions were confirmed by the data: Both RTs and error rates increased with increasing amount of topological transformation between two objects of the same category. Furthermore, RTs are sequentially additive, which is evidence that the topological transformation traverses intermediate points in the transformational path. Conclusions: Taken together, the data indicate that basic level recognition relies on time-consuming and error-prone topological transformation processes, which have an analog nature. The results support a model of basic level recognition that is based on analog (image-like) representations and analog transformation processes.},
   web_url = {http://journalofvision.org/1/3/98},
   institute = {Biologische Kybernetik},
   organization = {Max-Planck-Gesellschaft},
   event_place = {Sarasota, FL, USA},
   event_name = {First Annual Meeting of the Vision Sciences Society (VSS 2001)},
   DOI = {10.1167/1.3.98},
   author = {Graf, M}
}

@Poster { 1333,
   title = {Verformende Transformationsprozesse beim bild-basierten Erkennen von Objekten auf Kategorieebene},
   year = {2001},
   month = {3},
   pages = {109},
   abstract = {Eine Reihe von Befunden legt nahe, den bild-basierten Ansatz der Rekognition auf das Erkennen von Objekten auf der Basisebene der Kategorisierung (basic level) zu erweitern. Es ist allerdings noch nicht gekl{\"a}rt, wie das visuelle System Objekte auf der Basisebene erkennt. Wenn man verschiedene Mitglieder einer Kategorie auf Basisebene vergleicht, dann scheint es, dass die Formen der Kategoriemitglieder durch relativ einfache topologische (formver{\"a}ndernde) Transformationen ineinander {\"u}berf{\"u}hrt werden k{\"o}nnen. Dies gilt f{\"u}r die meisten biologischen Kategorien und auch f{\"u}r viele Artefakt-Kategorien. Diese nichteuklidischen topologischen Transformationen k{\"o}nnen durch die Dehnung bzw. Stauchung eines Gummituchs veranschaulicht werden. Die Studie geht von der Hypothese aus, dass Objekterkennung auf der Basisebene durch analoge topologische Transformationsprozesse erfolgt, welche die Stimulusrepr{\"a}sentation und die Objektrepr{\"a}sentation aufeinander ausrichten. Es ergaben sich somit die folgenden beiden Fragen: Zeigt sich bei der Kategorisierung eine Abh{\"a}ngigkeit der Performanz vom Umfang topologischer Transformationen? Falls systematische Effekte auftreten, sind diese durch analoge Transformationsprozesse verursacht?
Bilder von Objekten aus 16 biologischen und 14 artifiziellen Objektkategorien wurden gescannt. Mit Hilfe von Morphing Software wurden auf Basis von je zwei Objekten einer Kategorie zwischenliegende Objekte erzeugt, die ebenfalls dieser Kategorie angeh{\"o}ren. In jedem Trial wurden zwei maskierte Bilder sequenziell pr{\"a}sentiert (sequential matching task). Die transformationale Distanz zwischen beiden Bildern wurde variiert. Die Probanden mussten durch Tastendruck entscheiden, ob beide Bilder der selben Basiskategorie angeh{\"o}ren oder nicht.
Beide Vorhersagen wurden best{\"a}tigt: Zum einen erh{\"o}hten sich sowohl Reaktionszeiten als auch Fehlerraten mit zunehmendem Umfang der topologischen Transformation zwischen zwei Mitgliedern der selben Kategorie. Zum anderen waren die Reaktionszeiten sequenziell additiv, was Evidenz daf{\"u}r ist, dass die topologischen Transformationen zwischenliegende Punkte im transformationalen Pfad durchlaufen.
Das Erkennen von Objekten auf Basisebene scheint folglich auf zeitkonsumierenden und fehleranf{\"a}lligen topologischen Transformationsprozessen zu beruhen, die analoger Natur sind. Die Ergebnisse legen somit ein Modell nahe, das auf analogen (bildhaften) Repr{\"a}sentationen und analogen Transformationsprozessen basiert.},
   web_url = {http://www.twk.tuebingen.mpg.de/twk01/Pobjekt.htm},
   institute = {Biologische Kybernetik},
   organization = {Max-Planck-Gesellschaft},
   event_place = {T{\"u}bingen, Germany},
   event_name = {4. T{\"u}binger Wahrnehmungskonferenz (TWK 2001)},
   author = {Graf, M}
}

@Miscellaneous { 1329,
   title = {Objektkonstanz},
   journal = {Ged{\"a}chtnis und Erinnerung. Ein interdisziplin{\"a}res Lexikon},
   year = {2001},
   pages = {423-424},
   editor = {N. Pethes \& J. Ruchatz},
   institute = {Biologische Kybernetik},
   organization = {Max-Planck-Gesellschaft},
   author = {Graf, M}
}

@Conference { 4086,
   title = {The role of action representations in visual object recognition},
   journal = {Experimentelle Psychologie},
   year = {2006},
   month = {3},
   volume = {48},
   pages = {207},
   abstract = {Brain areas involved in action representation (premotor cortex, posterior parietal cortex) are activated when subjects name pictures of manipulable objects, like tools (e.g., Chao \& Martin, 2000). Moreover, behavioral evidence indicates that manipulable objects potentiate possible actions (e.g., Tucker \& Ellis, 1998). We investigated whether action representations facilitate object recognition.
Subjects were sequentially presented with two pictures of artifactual manipulable objects (e.g., tools, musical instruments) and were required to name the objects. In the congruent condition both objects afford similar actions, while they differ in the incongruent condition. Stimulus pairs in both conditions were matched for baseline naming accuracy, word frequency, word length, as well as visual and semantic similarity.
Naming accuracy was significantly higher in the congruent condition. This action priming effect substantiates our hypothesis that action representations play an important role in the recognition of artifactual manipulable objects.},
   department = {Department B{\"u}lthoff},
   talk_type = {Abstract Talk},
   institute = {Biologische Kybernetik},
   organization = {Max-Planck-Gesellschaft},
   event_place = {Mainz, Germany},
   event_name = {48. Tagung Experimentell Arbeitender Psychologen (TeaP 2006)},
   author = {Helbig, HB and Graf, M and Kiefer, M}
}

@Conference { 2452,
   title = {Koordinatentransformationen bei Objekterkennung und Handlungssteuerung},
   journal = {Experimentelle Psychologie},
   year = {2004},
   month = {4},
   volume = {46},
   abstract = {Um ein visuell wahrgenommenes Objekt greifen zu k{\"o}nnen, muss eine Umrechnung von Augenkoordinaten in Handkoordinaten erfolgen. Diese Koordinatentransformationen sind im Parietalkortex durch gain Modulation der neuronalen Antworten implementiert. W{\"a}hrend das Modell der zwei getrennten visuellen Str{\"o}me postuliert, dass Handlungssteuerung und Objekterkennung auf unterschiedlichen Verarbeitungsprinzipien beruhen, wird hier eine integrative Sichtweise vorgestellt, nach der das Erkennen r{\"a}umlich transformierter Objekte ebenfalls auf Koordinatentransformationen basiert: Durch Transformation des perzeptuellen Koordinatensystems werden Unterschiede in der r{\"a}umlichen Ausrichtung zwischen visuellem Input und den Ged{\"a}chtnisrepr{\"a}sentationen kompensiert. Diese Konzeption wird von zwei unterschiedlichen Forschungsrichtungen gest{\"u}tzt. Zum einen wurde demonstriert, dass auch Objekterkennen durch gain Modulation modelliert werden kann, und dass gain Modulations-Prozesse tats{\"a}chlich im ventralen Pfad auftreten. Zum andern zeigten psychophysische Experimente, dass Objekte besser erkannt werden, wenn zuvor ein anderes Objekt in der gleichen Orientierung dargeboten wurde. Dieser Kongruenzeffekt konnte f{\"u}r bekannte Objekte nachgewiesen werden, selbst wenn diese visuell un{\"a}hnlich sind, oder wenn die Objekte 
unterschiedliche Hauptachsen aufweisen.},
   department = {Department B{\"u}lthoff},
   web_url = {http://www.allpsych.uni-giessen.de/teap/programm_talks.php\#ueberblick},
   institute = {Biologische Kybernetik},
   organization = {Max-Planck-Gesellschaft},
   event_place = {Giessen, Germany},
   event_name = {46. Tagung Experimentell Arbeitender Psychologen (TeaP 2004)},
   author = {Graf, M}
}