@Proceedings{ VogelSWB2006, title = {APGV '06}, year = {2006}, month = {7}, pages = {164}, abstract = {From time to time, ACM SIGGRAPH has organized meetings centered around a specific theme to "bring together leading researchers and developers from a variety of disciplines to exchange state-of-the-art information and explore future directions for computer graphics." One such meeting on Perceptually Adaptive Graphics was held in Snowbird, Utah, in May of 2001 (http://isg.cs.tcd.ie/campfire/). This gathering brought together graphics researchers and vision scientists as well as others interested in the cross-section between the two fields. It formed the genesis of the ACM Symposium on Applied Perception in Graphics and Visualization (APGV), the success of which is evident in these proceedings.From its beginnings, APGV has continued this tradition of fostering interaction between computer graphics and vision science. By definition, computer graphics and visualization produces stimuli to be viewed by humans. The more that is known about the human visual system, the better such stimuli can be matched to those viewing them. This is a rich area where perception researchers can see their work applied directly. On the other hand, computer graphics techniques are maturing rapidly, and now constitute a viable approach to producing stimuli for use in psychophysics, thereby bypassing some of the difficulties inherent in experimental design. For instance, complex stimuli are easier to create using algorithms drawn from graphics.The first ACM Symposium on Applied Perception in Graphics and Visualization was held in Los Angeles in 2004, and was co-located with SIGGRAPH --- the premier conference in computer graphics. To promote greater participation of the perception community, the second symposium was co-located with the European Conference on Visual Perception (ECVP), held last year in A Coruña, Spain. This year, APGV is once more co-located with SIGGRAPH, and is held in Boston, July 28--30, 2006. Alongside the establishment of APGV, the Snowbird meeting was the spark needed to create a related ACM journal as well, called ACM Transactions on Applied Perception. It has a wider focus than APGV, and aims to foster interdisciplinary research which involves both perception and computing (i.e. not limited to computer graphics). This journal works in close collaboration with APGV, and has produced a special issue for each of the two preceding APGV symposia. These special issues publish a selection of the best APGV papers in expanded format.New this year is the establishment of a dedicated website for APGV: http://www.apgv.org, which will host all information pertinent to this symposium. In addition, a steering committee was established that will oversee the continuity between successive symposia, and will coordinate their organization. The steering committee is currently composed of Heinrich Bülthoff, Alan Chalmers, Victoria Interrante, Ann McNamara and Erik Reinhard. Getting involved with the organization of APGV is highly encouraged, and any of the steering committee members would be delighted to listen to your ideas and suggestions.The papers submitted to this year's APGV were of the usual very high quality. We have accepted 20 out of 45 submissions for paper presentation. The poster program drew a further 22 posters. These statistics are very much in-line with previous years' efforts, as shown in Table 1. APGV thus continues to attract strong contributions in a wide range of topics. As a result, we are very pleased to present the Proceedings of the Third Symposium on Applied Perception in Graphics and Visualization.}, web_url = {http://dl.acm.org/citation.cfm?id=1140491}, publisher = {ACM Press}, address = {New York, NY, USA}, event_name = {3rd Symposium on Applied Perception in Graphics and Visualization (APGV 2006)}, event_place = {Boston, MA, USA}, state = {published}, ISBN = {1-59593-429-4}, author = {Fleming RW{roland}{Department Human Perception, Cognition and Action}; Kim S} } @Article{ GaissertWFB2012, title = {Haptic Categorical Perception of Shape}, journal = {PLoS One}, year = {2012}, month = {8}, volume = {7}, number = {8}, pages = {1-7}, abstract = {Categorization and categorical perception have been extensively studied, mainly in vision and audition. In the haptic domain, our ability to categorize objects has also been demonstrated in earlier studies. Here we show for the first time that categorical perception also occurs in haptic shape perception. We generated a continuum of complex shapes by morphing between two volumetric objects. Using similarity ratings and multidimensional scaling we ensured that participants could haptically discriminate all objects equally. Next, we performed classification and discrimination tasks. After a short training with the two shape categories, both tasks revealed categorical perception effects. Training leads to between-category expansion resulting in higher discriminability of physical differences between pairs of stimuli straddling the category boundary. Thus, even brief training can alter haptic representations of shape. This suggests that the weights attached to various haptic shape features can be changed dynamically in response to top-down information about class membership.}, web_url = {http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0043062}, state = {published}, DOI = {10.1371/journal.pone.0043062}, EPUB = {e43062}, author = {Gaissert N{ninagaissert}{Department Human Perception, Cognition and Action}; Waterkamp S{swaterka}{Department Human Perception, Cognition and Action}; Fleming RW{roland}{Department Human Perception, Cognition and Action}; B\"ulthoff I{isa}{Department Human Perception, Cognition and Action}} } @Article{ FlemingHB2011, title = {Estimation of 3D shape from image orientations}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, year = {2011}, month = {12}, volume = {108}, number = {51}, pages = {20438-20443}, abstract = {One of the main functions of vision is to estimate the 3D shape of objects in our environment. Many different visual cues, such as stereopsis, motion parallax, and shading, are thought to be involved. One important cue that remains poorly understood comes from surface texture markings. When a textured surface is slanted in 3D relative to the observer, the surface patterns appear compressed in the retinal image, providing potentially important information about 3D shape. What is not known, however, is how the brain actually measures this information from the retinal image. Here, we explain how the key information could be extracted by populations of cells tuned to different orientations and spatial frequencies, like those found in the primary visual cortex. To test this theory, we created stimuli that selectively stimulate such cell populations, by “smearing” (filtering) images of 2D random noise into specific oriented patterns. We find that the resulting patterns appear vividly 3D, and that increasing the strength of the orientation signals progressively increases the sense of 3D shape, even though the filtering we apply is physically inconsistent with what would occur with a real object. This finding suggests we have isolated key mechanisms used by the brain to estimate shape from texture. Crucially, we also find that adapting the visual system's orientation detectors to orthogonal patterns causes unoriented random noise to look like a specific 3D shape. Together these findings demonstrate a crucial role of orientation detectors in the perception of 3D shape.}, web_url = {http://www.pnas.org/content/108/51/20438.full.pdf+html}, state = {published}, DOI = {10.1073/pnas.1114619109}, author = {Fleming RW{roland}{Department Human Perception, Cognition and Action}; Holtmann-Rice D{dhr}{Department Human Perception, Cognition and Action}; B\"ulthoff HH{hhb}{Department Human Perception, Cognition and Action}} } @Article{ FlemingJM2011, title = {Visual Perception of Thick Transparent Materials}, journal = {Psychological Science}, year = {2011}, month = {6}, volume = {22}, number = {6}, pages = {812-820}, abstract = {Under typical viewing conditions, human observers readily distinguish between materials such as silk, marmalade, or granite, an achievement of the visual system that is poorly understood. Recognizing transparent materials is especially challenging. Previous work on the perception of transparency has focused on objects composed of flat, infinitely thin filters. In the experiments reported here, we considered thick transparent objects, such as ice cubes, which are irregular in shape and can vary in refractive index. An important part of the visual evidence signaling the presence of such objects is distortions in the perceived shape of other objects in the scene. We propose a new class of visual cues derived from the distortion field induced by thick transparent objects, and we provide experimental evidence that cues arising from the distortion field predict both the successes and the failures of human perception in judging refractive indices.}, web_url = {http://pss.sagepub.com/content/22/6/812.full.pdf+html}, state = {published}, DOI = {10.1177/0956797611408734}, author = {Fleming RW{roland}{Department Human Perception, Cognition and Action}; J\"akel F{frank}; Maloney LT{ltm}} } @Article{ 6849, title = {Perceived Object Stability Depends on Multisensory Estimates of Gravity}, journal = {PLoS ONE}, year = {2011}, month = {4}, volume = {6}, number = {4}, pages = {1-5}, abstract = {Background How does the brain estimate object stability? Objects fall over when the gravity-projected centre-of-mass lies outside the point or area of support. To estimate an object's stability visually, the brain must integrate information across the shape and compare its orientation to gravity. When observers lie on their sides, gravity is perceived as tilted toward body orientation, consistent with a representation of gravity derived from multisensory information. We exploited this to test whether vestibular and kinesthetic information affect this visual task or whether the brain estimates object stability solely from visual information. Methodology/Principal Findings In three body orientations, participants viewed images of objects close to a table edge. We measured the critical angle at which each object appeared equally likely to fall over or right itself. Perceived gravity was measured using the subjective visual vertical. The results show that the perceived critical angle was significantly biased in the same direction as the subjective visual vertical (i.e., towards the multisensory estimate of gravity). Conclusions/Significance Our results rule out a general explanation that the brain depends solely on visual heuristics and assumptions about object stability. Instead, they suggest that multisensory estimates of gravity govern the perceived stability of objects, resulting in objects appearing more stable than they are when the head is tilted in the same direction in which they fall.}, web_url = {http://www.plosone.org/article/fetchObjectAttachment.action;jsessionid=C1AE6461C55EF186CAA1AB710C6E0EAA.ambra02?uri=info%3Adoi%2F10.1371%2Fjournal.pone.0019289&representation=PDF}, state = {published}, DOI = {10.1371/journal.pone.0019289}, EPUB = {e19289}, author = {Barnett-Cowan M{mbc}{Department Human Perception, Cognition and Action}; Fleming RW{roland}{Department Human Perception, Cognition and Action}; Singh M; B\"ulthoff HH{hhb}{Department Human Perception, Cognition and Action}} } @Article{ 5741, title = {Categorizing art: Comparing humans and computers}, journal = {Computers and Graphics}, year = {2009}, month = {8}, volume = {33}, number = {4}, pages = {484-495}, abstract = {The categorization of art (paintings, literature) into distinct styles such as Expressionism, or Surrealism has had a profound influence on how art is presented, marketed, analyzed, and historicized. Here, we present results from human and computational experiments with the goal of determining to which degree such categories can be explained by simple, low-level appearance information in the image. Following experimental methods from perceptual psychology on category formation, naive, non-expert participants were first asked to sort printouts of artworks from different art periods into categories. Converting these data into similarity data and running a multi-dimensional scaling (MDS) analysis, we found distinct categories which corresponded sometimes surprisingly well to canonical art periods. The result was cross-validated on two complementary sets of artworks for two different groups of participants showing the stability of art interpretation. The second focus of this paper was on determining how far computational algorithms would be able to capture human performance or would be able in general to separate different art categories. Using several state-of-the-art algorithms from computer vision, we found that whereas low-level appearance information can give some clues about category membership, human grouping strategies included also much higher-level concepts.}, web_url = {http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6TYG-4W6Y829-1-S&_cdi=5618&_user=29041&_orig=search&_coverDate=08%2F31%2F2009&_sk=999669995&view=c&wchp=dGLbVzW-zSkWA&md5=26d1582bdc926c6b79e4abe6c4f3b637&ie=/sdarticle.pdf}, state = {published}, DOI = {10.1016/j.cag.2009.04.003}, author = {Wallraven C{walli}{Department Human Perception, Cognition and Action}; Fleming R{roland}{Department Human Perception, Cognition and Action}; Cunningham DW{dwc}{Department Human Perception, Cognition and Action}; Rigau J; Feixas M; Sbert M} } @Article{ 6219, title = {Guest editorial: Special issue on Applied Perception in Graphics and Visualization (APGV07)}, journal = {ACM Transactions on Applied Perception}, year = {2009}, month = {1}, volume = {5}, number = {4:18}, web_url = {http://dl.acm.org/citation.cfm?doid=1462048.1462049}, state = {published}, DOI = {10.1145/1462048.1462049}, author = {Fleming RW{roland}{Department Human Perception, Cognition and Action}; Langer M{mlanger}} } @Article{ 4134, title = {Image-based material editing}, journal = {ACM Transactions on Graphics}, year = {2006}, month = {7}, volume = {25}, number = {3}, pages = {654-663}, abstract = {Photo editing software allows digital images to be blurred, warped or re-colored at the touch of a button. However, it is not currently possible to change the material appearance of an object except by painstakingly painting over the appropriate pixels. Here we present a method for automatically replacing one material with another, completely different material, starting with only a single high dynamic range image as input. Our approach exploits the fact that human vision is surprisingly tolerant of certain (sometimes enormous) physical inaccuracies, while being sensitive to others. By adjusting our simulations to be careful about those aspects to which the human visual system is sensitive, we are for the first time able to demonstrate significant material changes on the basis of a single photograph as input.}, file_url = {/fileadmin/user_upload/files/publications/ImageBasedMaterialEditing_4134[0].pdf}, state = {published}, DOI = {http://doi.acm.org/10.1145/1179352.1141937}, author = {Khan EA; Reinhard E; Fleming RW{roland}{Department Human Perception, Cognition and Action}; B\"ulthoff HH{hhb}{Department Human Perception, Cognition and Action}} } @Article{ 4371, title = {Sketching Shiny Surfaces: 3D Shape Extraction and Depiction of Specular Surfaces}, journal = {ACM Transactions on Applied Perception}, year = {2006}, month = {7}, volume = {3}, number = {3}, pages = {262-285}, abstract = {Many materials including water, plastic and metal have specular surface characteristics. Specular reflections have commonly been considered a nuisance for the recovery of object shape. However, the way that reflections are distorted across the surface depends crucially on 3D curvature, suggesting that they could in fact be a useful source of information. Indeed, observers can have a vivid impression of 3D shape when an object is perfectly mirrored (i.e. the image contains nothing but specular reflections). This leads to the question what are the underlying mechanisms of our visual system to extract this 3D shape information from a perfectly mirrored object. In this paper we propose a biologically motivated recurrent model for the extraction of visual features relevant for the perception of 3D shape information from images of mirrored objects. We analyze qualitatively and quantitatively the results of computational model simulations and show that bidirectional recurrent information processing leads to better r esults then pure feedforward processing. Furthermore we utilize the model output to create a rough non-photorealistic sketch representation of a mirrored object, which emphasizes image features that are mandatory for 3D shape perception (e.g. occluding contour, regions of high curvature). Moreover, this sketch illustrates that the model generates a representation of object features independent of the surrounding scene reflected in the mirrored object.}, file_url = {/fileadmin/user_upload/files/publications/weidenbacher_TAP_paper_4371[0].pdf}, web_url = {http://doi.acm.org/10.1145/1166087.1166094}, state = {published}, DOI = {http://doi.acm.org/10.1145/1166087.1166094}, author = {Weidenbacher U; Bayerl P; Neumann H; Fleming R{roland}{Department Human Perception, Cognition and Action}} } @Article{ 3465, title = {Low-Level Images Cues in the Perception of Translucent Materials}, journal = {ACM Transactions on Applied Perception}, year = {2005}, month = {7}, volume = {2}, number = {3}, pages = {346-382}, abstract = {When light strikes a translucent material (such as wax, milk or fruit flesh), it enters the body of the object, scatters and re-emerges from the surface. The diffusion of light through translucent materials gives them a characteristic visual softness and glow. What image properties underlie this distinctive appearance? What cues allow us to tell whether a surface is translucent or opaque? Previous work on the perception of semi-transparent materials was based on a very restricted physical model of thin filters [Metelli 1970; 1974a,b]. However, recent advances in computer graphics [Jensen et al. 2000; Jensen and Buhler 2002] allow us to efficiently simulate the complex sub-surface light transport effects that occur in real translucent objects. Here we use this model to study the perception of translucency, using a combination of psychophysics and image statistics. We find that many of the cues that were traditionally thought to be important for semi-transparent filters (e.g., X-junctions) are not relevant for solid translucent objects. We discuss the role of highlights, colour, object size, contrast, blur and lighting direction in the perception of translucency. We argue that the physics of translucency are too complex for the visual system to estimate intrinsic physical parameters by inverse optics. Instead, we suggest that we identify translucent materials by parsing them into key regions and by gathering image statistics from these regions.}, file_url = {/fileadmin/user_upload/files/publications/fleming-buelthoff-acm-tap-2005_3465[0].pdf}, web_url = {http://doi.acm.org/10.1145/1077399.1077409}, state = {published}, DOI = {doi.acm.org/10.1145/1077399.1077409}, author = {Fleming R{roland}{Department Human Perception, Cognition and Action}; B\"ulthoff HH{hhb}{Department Human Perception, Cognition and Action}} } @Article{ 2601, title = {Specular reflections and the perception of shape}, journal = {Journal of Vision}, year = {2004}, month = {9}, volume = {4}, number = {9}, pages = {798-820}, abstract = {Many materials, including leaves, water, plastic, and chrome exhibit specular reflections. It seems reasonable that the visual system can somehow exploit specular reflections to recover three-dimensional (3D) shape. Previous studies (e.g., J. T. Todd & E. Mingolla, 1983; J. F. Norman, J. T. Todd, & G. A. Orban, 2004) have shown that specular reflections aid shape estimation, but the relevant image information has not yet been isolated. Here we explain how specular reflections can provide reliable and accurate constraints on 3D shape. We argue that the visual system can treat specularities somewhat like textures, by using the systematic patterns of distortion across the image of a specular surface to recover 3D shape. However, there is a crucial difference between textures and specularities: In the case of textures, the image compressions depend on the first derivative of the surface depth (i.e., surface orientation), whereas in the case of specularities, the image compressions depend on the second derivative (i.e., surfaces curvatures). We suggest that this difference provides a cue that can help the visual system distinguish between textures and specularities, even when present simultaneously. More importantly, we show that the dependency of specular distortions on the second derivative of the surface leads to distinctive fields of image orientation as the reflected world is warped across the surface. We find that these “orientation fields” are (i) diagnostic of 3D shape, (ii) remain surprisingly stable when the world reflected in the surface is changed, and (iii) can be extracted from the image by populations of simple oriented filters. Thus the use of specular reflections for 3D shape perception is both easier and more reliable than previous computational work would suggest.}, web_url = {http://www.journalofvision.org/content/4/9/10.long}, state = {published}, DOI = {10.1167/4.9.10}, author = {Fleming RW{roland}{Department Human Perception, Cognition and Action}; Torralba A; Adelson EH} } @Article{ 2555, title = {Real world illumination and the perception of surface reflectance properties}, journal = {Journal of Vision}, year = {2003}, month = {7}, volume = {3}, number = {5:3}, pages = {347-368}, abstract = {Under typical viewing conditions, we find it easy to distinguish between different materials, such as metal, plastic, and paper. Recognizing materials from their surface reflectance properties (such as lightness and gloss) is a nontrivial accomplishment because of confounding effects of illumination. However, if subjects have tacit knowledge of the statistics of illumination encountered in the real world, then it is possible to reject unlikely image interpretations, and thus to estimate surface reflectance even when the precise illumination is unknown. A surface reflectance matching task was used to measure the accuracy of human surface reflectance estimation. The results of the matching task demonstrate that subjects can match surface reflectance properties reliably and accurately in the absence of context, as long as the illumination is realistic. Matching performance declines when the illumination statistics are not representative of the real world. Together these findings suggest that subjects do use stored assumptions about the statistics of real-world illumination to estimate surface reflectance. Systematic manipulations of pixel and wavelet properties of illuminations reveal that the visual system’s assumptions about illumination are of intermediate complexity (e.g., presence of edges and bright light sources), rather than of high complexity (e.g., presence of recognizable objects in the environment).}, web_url = {http://journalofvision.org/3/5/3/}, state = {published}, DOI = {10.1167/3.5.3}, author = {Fleming RW{roland}; Dror RO; Adelson EH} } @Article{ 2552, title = {The Interpolation of Object and Surface Structure.}, journal = {Cognitive Psychology}, year = {2002}, volume = {44}, pages = {148-190}, state = {published}, author = {Anderson BL; Singh M; Fleming RW{roland}} } @Inproceedings{ MasiaFSG2010, title = {Selective Reverse Tone Mapping}, year = {2010}, month = {9}, pages = {1-10}, abstract = {High dynamic range (HDR) displays are becoming more common, which has given rise to a number of reverse tone mapping techniques. The goal of these techniques is to expand the dynamic range of all the existing low dynamic range content to t that of these displays. Most of the reverse tone mapping operators , however, fail to oer a good solution in cases where the input images contain large saturated areas. In this paper we present an interactive higher-level approach to reverse tone mapping. Inspired by the Zone System used in photography, it can also be used as an artistic tool where both the tonal balance and the mood of the nal depiction can be adjusted by the user.}, file_url = {fileadmin/user_upload/files/publications/CEIG-2010-Masia.pdf}, web_url = {https://www.semanticscholar.org/paper/Selective-Reverse-Tone-Mapping-Masia-Fleming/3600c1b0c8e22b554f5351210e83a3f379d9e4ff}, event_name = {Congreso Español de Informática Gráfica (CEIG 2010)}, event_place = {Valencia, Spain}, state = {published}, author = {Masia B; Fleming R{roland}{Department Human Perception, Cognition and Action}; Sorkine O; Gutierrez D} } @Inproceedings{ ChuangBBF2010, title = {Measuring unrestrained gaze on wall-sized displays}, year = {2010}, month = {8}, pages = {347-348}, abstract = {Motivation -- Natural gaze involves the coordinated movements of eye, head and torso. This allows access to a wide field of view, up to a range of 260° (Chen, Solinger, Poncet & Lancet, 1999). The recent increase in large displays places a demand on being able to track a mobile user's gaze over this extensive range. Research approach -- We developed an extensible system for measuring the gaze of users on wall-sized displays. Our solution combines the inputs of a conventional head-mounted eyetracker (Eyelink2©, SR Research) and motion-capture system (Vicon MX©, Vicon), to provide real-time measurements of a mobile user's gaze in 3D space. Findings/Design -- The presented system serves as a single platform for studying user behavior across a wide range of tasks: single-step saccade shifts, free-viewing of natural scenes, visual search and gaze-assisted user interfaces. Importantly, it allows eye- and head-movements to be separately measured without compromising the accuracy of combined gaze measurements. Take away message -- Unrestrained gaze movements on a large display can be accurately measured by suitably combining the inputs of conventional eye- and body-tracking hardware.}, web_url = {http://ecce2010.tudelft.nl/}, editor = {Neerincx, W. , W-P Brinkman}, publisher = {ACM Press}, address = {New York, NY, USA}, event_name = {28th Annual European Conference on Cognitive Ergonomics (ECCE '10)}, event_place = {Delft, Netherlands}, state = {published}, ISBN = {978-1-60558-946-6}, DOI = {10.1145/1962300.1962379}, author = {Chuang LL{chuang}{Department Human Perception, Cognition and Action}; Bieg H-J{bieg}{Department Human Perception, Cognition and Action}; B\"ulthoff HH{hhb}{Department Human Perception, Cognition and Action}; Fleming RW{roland}{Department Human Perception, Cognition and Action}} } @Inproceedings{ 6246, title = {Eye and Pointer Coordination in Search and Selection Tasks}, year = {2010}, month = {3}, pages = {89-92}, abstract = {Selecting a graphical item by pointing with a computer mouse is a ubiquitous task in many graphical user interfaces. Several techniques have been suggested to facilitate this task, for instance, by reducing the required movement distance. Here we measure the natural coordination of eye and mouse pointer control across several search and selection tasks. We find that users automatically minimize the distance to likely targets in an intelligent, task dependent way. When target location is highly predictable, top-down knowledge can enable users to initiate pointer movements prior to target fixation. These findings ques-tion the utility of existing assistive pointing techniques and suggest that alternative approaches might be more effective.}, file_url = {/fileadmin/user_upload/files/publications/ETRA2010-Bieg_6246[0].pdf}, web_url = {http://etra.cs.uta.fi/}, editor = {Morimoto, C. H., H. Istance, A. Hyrskykari, Q. Ji}, publisher = {ACM Press}, address = {New York, NY, USA}, event_name = {Symposium on Eye Tracking Research and Applications (ETRA 2010)}, event_place = {Austin, TX, USA}, state = {published}, ISBN = {978-1-60558-994-7}, DOI = {10.1145/1743666.1743688}, author = {Bieg H-J{bieg}{Department Human Perception, Cognition and Action}; Chuang LL{chuang}{Department Human Perception, Cognition and Action}; Fleming RW{roland}{Department Human Perception, Cognition and Action}; Reiterer H; B\"ulthoff HH{hhb}{Department Human Perception, Cognition and Action}} } @Inproceedings{ 6218, title = {Evaluation of reverse tone mapping through varying exposure conditions}, journal = {ACM Transactions on Graphics}, year = {2009}, month = {12}, volume = {28}, number = {5:160}, pages = {1-8}, abstract = {Most existing image content has low dynamic range (LDR), which necessitates effective methods to display such legacy content on high dynamic range (HDR) devices. Reverse tone mapping operators (rTMOs) aim to take LDR content as input and adjust the contrast intelligently to yield output that recreates the HDR experience. In this paper we show that current rTMO approaches fall short when the input image is not exposed properly. More specifically, we report a series of perceptual experiments using a Brightside HDR display and show that, while existing rTMOs perform well for under-exposed input data, the perceived quality degrades substantially with over-exposure, to the extent that in some cases subjects prefer the LDR originals to images that have been treated with rTMOs. We show that, in these cases, a simple rTMO based on gamma expansion avoids the errors introduced by other methods, and propose a method to automatically set a suitable gamma value for each image, based on the image key and empirical data. We validate the results both by means of perceptual experiments and using a recent image quality metric, and show that this approach enhances visible details without causing artifacts in incorrectly-exposed regions. Additionally, we perform another set of experiments which suggest that spatial artifacts introduced by rTMOs are more disturbing than inaccuracies in the expanded intensities. Together, these findings suggest that when the quality of the input data is unknown, reverse tone mapping should be handled with simple, non-aggressive methods to achieve the desired effect.}, web_url = {http://giga.cps.unizar.es/~diegog/ficheros/pdf_papers/Masia_rTM_sAsia09.pdf}, publisher = {ACM Press}, address = {New York, NY, USA}, event_name = {2nd ACM SIGGRAPH Conference and Exhibition in Asia (SIGGRAPH Asia 2009)}, event_place = {Yokohama, Japan}, state = {published}, DOI = {10.1145/1618452.1618506}, author = {Masia B; Agustin S; Fleming RW{roland}{Department Human Perception, Cognition and Action}; Sorkine O; Gutierrez D} } @Inproceedings{ FlemingS2009, title = {Visual perception of 3D shape}, year = {2009}, month = {8}, pages = {24}, abstract = {The human brain has the remarkable ability to turn 2D retinal images of an object into a vivid perception of the object's 3D shape. Mathematically, this should be impossible, and yet we do it effortlessly whenever we open our eyes. How does the brain achieve this? This course presents a number of key findings from the study of human visual perception of 3D shape. It shows how different sources of image information such as contours, texture gradients, shading, and optic flow each contribute to the reconstruction of 3D shape by the human visual system. The course also summarizes what happens when 3D shape perception fails, leading to some cool illusions, and describes current ideas about how 3D shapes are parsed and represented, and relates these ides to theories of 2D shape encoding. Throughout the course, connections will be made to common practices in the artistic depiction of 3D form. The course concludes with a discussion of how an understanding of human shape perception might be leveraged to enhance 3D shape visualization in photorealistic and non-photorealistic rendering. This course should be of interest to graphics researchers and practitioners who want to understand the portrayal of shape and, more broadly, anyone who is curious about human vision.}, web_url = {http://dl.acm.org/citation.cfm?doid=1667239.1667263}, publisher = {ACM Press}, address = {New York, NY, USA}, booktitle = {ACM SIGGRAPH 2009 Courses}, event_name = {36th International Conference and Exhibition on Computer Graphics and Interactive Techniques (SIGGRAPH 2009)}, event_place = {New Orleans, LA, USA}, state = {published}, DOI = {10.1145/1667239.1667263}, author = {Fleming RW{roland}{Department Human Perception, Cognition and Action}; Singh M} } @Inproceedings{ 5736, title = {Image statistics for clustering paintings according to their visual appearance}, year = {2009}, month = {5}, pages = {57-64}, abstract = {Untrained observers readily cluster paintings from different art periods into distinct groups according to their overall visual appearance or 'look' [WCF08]. These clusters are typically influenced by both the content of the paintings (e.g. portrait, landscape, still-life, etc.), and stylistic considerations (e.g. the 'flat' appearance of Gothic paintings, or the distinctive use of colour in Fauve works). Here we aim to identify a set of image measurements that can capture this 'naïve visual impression of art', and use these features to automatically cluster a database of images of paintings into appearance-based groups, much like an untrained observer. We combine a wide range of features from simple colour statistics, through mid-level spatial features to high-level properties, such as the output of face-detection algorithms, which are intended to correlate with semantic content. Together these features yield clusters of images that look similar to one another despite differences in historical period and content. In addition, we tested the performance of the feature library in several classification tasks yielding good results. Our work could be applied as a curatorial or research aid, and also provides insight into the image attributes that untrained subjects may attend to when judging works of art.}, file_url = {/fileadmin/user_upload/files/publications/CAe2009_final_[0].pdf}, web_url = {http://www.cs.rug.nl/svcg/cae2009/pmwiki.php/Main/Program}, editor = {Deussen, O. , D. W. Fellner, N. A. Dodgson}, publisher = {Eurographics}, address = {Aire-La-Ville, Switzerland}, booktitle = {Computational Aesthetics 2009}, event_name = {Eurographics Workshop on Computational Aesthetics in Graphics, Visualization and Imaging}, event_place = {Victoria, BC, Canada}, state = {published}, ISBN = {978-3-905674-17-0}, DOI = {10.2312/COMPAESTH/COMPAESTH09/057-064}, author = {Spehr M{mspehr}{Department Human Perception, Cognition and Action}; Wallraven C{walli}{Department Human Perception, Cognition and Action}; Fleming RW{roland}{Department Human Perception, Cognition and Action}} } @Inproceedings{ 5470, title = {LibGaze: Real-time gaze-tracking of freely moving observers for wall-sized displays}, year = {2008}, month = {10}, pages = {101-110}, abstract = {We present a mobile system for tracking the gaze of an observer in real-time as they move around freely and interact with a wall-sized display. The system combines a head-mounted eye tracker with a mo- tion capture system for tracking markers attached to the eye tracker. Our open-source software library libGaze provides routines for calibrating the sys- tem and computing the viewer’s position and gaze direction in real-time. The modular architecture of our system supports simple replacement of each of the main components with alternative technology. We use the system to perform a psychophysical user-study, designed to measure how users visually explore large displays. We find that observers use head move- ments during gaze shifts, even when these are well within the range that can be com- fortably reached by eye movements alone. This suggests that free movement is important in nor- mal gaze behaviour,motivating further applications in which the tracked user is free to move.}, file_url = {fileadmin/user_upload/files/publications/VMV-2008-Herholz.pdf}, web_url = {https://www.researchgate.net/publication/264879670_LibGaze_Real-time_gaze-tracking_of_freely_moving_observers_for_wall-sized_displays_Vision_Modeling_and_Visualization_Proceedings}, editor = {Deussen, O. , D. Keim}, publisher = {IOS Press}, address = {Amsterdam, Netherlands}, event_name = {13th International Fall Workshop on Vision, Modeling, and Visualization (VMV 2008)}, event_place = {Konstanz, Germany}, state = {published}, author = {Herholz S{sherholz}{Department Human Perception, Cognition and Action}; Chuang LL{chuang}{Department Human Perception, Cognition and Action}; Tanner TG{tanner}{Department Human Perception, Cognition and Action}; B\"ulthoff HH{hhb}{Department Human Perception, Cognition and Action}; Fleming RW{roland}{Department Human Perception, Cognition and Action}} } @Inproceedings{ 5732, title = {Understanding exposure for reverse tone mapping}, year = {2008}, month = {9}, pages = {189-198}, abstract = {High dynamic range (HDR) displays are capable of providing a rich visual experience by boosting both luminance and contrast beyond what conventional displays can offer.We envision that HDR capture and display hardware will soon reach the mass market and become mainstream in most fields, from entertainment to scientific visualization. This will necessarily lead to an extensive redesign of the imaging pipeline. However, a vast amount of legacy content is available, captured and stored using the traditional, low dynamic range (LDR) pipeline. The immediate question that arises is: will our current LDR digital material be properly visualized on an HDR display? The answer to this question involves the process known as reverse tone mapping (the expansion of luminance and contrast to match those of the HDR display) for which no definite solution exists. This paper studies the specific problem of reverse tone mapping for imperfect legacy still images, where some regions are under- or overexposed. First, we show the results of a psychophysical study compared with first-order image statistics, in an attempt to gain some understanding in what makes an image be perceived as incorrectly exposed; second, we propose a methodology to evaluate existing reverse tone mapping algorithms in the case of imperfect legacy content.}, file_url = {/fileadmin/user_upload/files/publications/CEIG08-Fleming_5732[0].pdf}, web_url = {https://diglib.eg.org/handle/10.2312/LocalChapterEvents.CEIG.CEIG08.189-197}, editor = {Matey, L. , J. C. Torres}, publisher = {Eurographics Association}, address = {Aire-la-Ville, Switzerland}, event_name = {XVIII. Congreso Español de Informática Gráfica (CEIG 2008)}, event_place = {Barcelona, Spain}, state = {published}, ISBN = {978-3-905673-69-2}, DOI = {10.2312/LocalChapterEvents/CEIG/CEIG08/189-197}, author = {Martin M; Fleming RW{roland}{Department Human Perception, Cognition and Action}; Sorkine O; Gutierrez D} } @Inproceedings{ 5163, title = {Perceptual and Computational Categories in Art}, year = {2008}, month = {6}, pages = {131-138}, abstract = {The categorization of art (paintings, literature) into distinct styles such as expressionism, or surrealism has had a profound influence on how art is presented, marketed, analyzed, and historicized. Here, we present results from several perceptual experiments with the goal of determining whether such categories also have a perceptual foundation. Following experimental methods from perceptual psychology on category formation, naive, non-expert participants were asked to sort printouts of artworks from different art periods into categories. Converting these data into similarity data and running a multi-dimensional scaling (MDS) analysis, we found distinct perceptual categories which did in some cases correspond to canonical art periods. Initial results from a comparison with several computational algorithms for image analysis and scene categorization are also reported.}, file_url = {/fileadmin/user_upload/files/publications/CAE2008-Wallraven_5163[0].pdf}, web_url = {http://diglib.eg.org/handle/10.2312/COMPAESTH.COMPAESTH08.131-138}, editor = {Cunningham, D.W. , V. Interrante, P. Brown, J. McCormack}, publisher = {Eurographics Association}, address = {Aire-la-Ville, Switzerland}, event_name = {Computational Aesthetics 2008: Eurographics Workshop on Computational Aesthetics (CAe 2008)}, event_place = {Lisboa, Portugal}, state = {published}, ISBN = {978-3-905674-08-8}, DOI = {10.2312/COMPAESTH/COMPAESTH08/131-138}, author = {Wallraven C{walli}{Department Human Perception, Cognition and Action}; Cunningham DW{dwc}{Department Human Perception, Cognition and Action}; Fleming R{roland}{Department Human Perception, Cognition and Action}} } @Inproceedings{ 4651, title = {Distortion in 3D shape estimation with changes in illumination}, year = {2007}, month = {7}, pages = {99-105}, abstract = {In many domains it is very important that observers form an accurate percept of 3-dimensional structure from 2-dimensional images of scenes or objects. This is particularly relevant for designers who need to make decisions concerning the refinement of novel objects that haven't been physically built yet. This study presents the results of two experiments whose goal was to test the effect of lighting direction on the shape perception of smooth surfaces using shading and lighting techniques commonly used in modeling and design software. The first experiment consisted of a 2 alternate forced choice task which compared the effect of the amount of shape difference between smooth surfaces lit by a single point light with whether the position of the light sources were the same or different for each surface. Results show that, as the difference between the shapes decreased, participants were more and more biased towards choosing the match shape lit by the same source as the test shape. In the second experiment, participants had to report the orientation at equivalent probe locations on pairs of smooth surfaces presented simultaneously, using gauge figures. The surfaces could either be the same or slightly different and the light source of each shape could either be at the same relative location or offset by 90° horizontally. Participants reported large differences in surface orientation when the lighting condition was different, even when the shapes were the same, confirming the first results. Our findings show that lighting conditions can have a strong effect on 3-dimensional perception, and suggest that great care should be taken when projection systems are used for 3D visualisation where an accurate representation is required, either by carefully choosing lighting conditions or by using more realistic rendering techniques.}, file_url = {/fileadmin/user_upload/files/publications/apgv07-99_[0].pdf}, web_url = {http://www.apgv.de/}, editor = {Wallraven, C. , V. Sundstedt}, publisher = {ACM Press}, address = {New York, NY, USA}, event_name = {4th Symposium on Applied Perception in Graphics and Visualization (APGV 2007)}, event_place = {Tübingen, Germany}, state = {published}, ISBN = {978-1-59593-670-7}, DOI = {10.1145/1272582.1272602}, author = {Caniard F{franck}{Department Human Perception, Cognition and Action}; Fleming RW{roland}{Department Human Perception, Cognition and Action}} } @Inproceedings{ 4791, title = {Do HDR displays support LDR content?: a psychophysical evaluation}, journal = {ACM Transactions on Graphics}, year = {2007}, month = {7}, volume = {26}, number = {3:38}, pages = {1-7}, abstract = {The development of high dynamic range (HDR) imagery has brought us to the verge of arguably the largest change in image display technologies since the transition from black-and-white to color television. Novel capture and display hardware will soon enable consumers to enjoy the HDR experience in their own homes. The question remains, however, of what to do with existing images and movies, which are intrinsically low dynamic range (LDR). Can this enormous volume of legacy content also be displayed effectively on HDR displays? We have carried out a series of rigorous psychophysical investigations to determine how LDR images are best displayed on a state-of-the-art HDR monitor, and to identify which stages of the HDR imaging pipeline are perceptually most critical. Our main findings are: (1) As expected, HDR displays outperform LDR ones. (2) Surprisingly, HDR images that are tonemapped for display on standard monitors are often no better than the best single LDR exposure from a bracketed sequence. (3) Most impor tantly of all, LDR data does not necessarily require sophisticated treatment to produce a compelling HDR experience. Simply boosting the range of an LDR image linearly to fit the HDR display can equal or even surpass the appearance of a true HDR image. Thus the potentially tricky process of inverse tone mapping can be largely circumvented.}, file_url = {/fileadmin/user_upload/files/publications/SIGGRAPH07_camera_ready_[0].pdf}, web_url = {http://portal.acm.org/toc.cfm?id=1276377&amp;coll=portal&amp;dl=ACM&amp;type=issue&amp;idx=J778&amp;part=transaction&amp;WantType=Transactions&amp;title=ACM%20Transactions%20on%20Graphics%20%28TOG%29}, publisher = {ACM Press}, address = {New York, NY, USA}, event_name = {34th International Conference and Exhibition on Computer Graphics and Interactive Techniques (SIGGRAPH 2007)}, event_place = {San Diego, CA, USA}, state = {published}, DOI = {10.1145/1275808.1276425}, author = {Akyuz AO{akyuz}{Department Human Perception, Cognition and Action}; Fleming RW{roland}{Department Human Perception, Cognition and Action}; Riecke BE{bernie}{Department Human Perception, Cognition and Action}; Reinhard E; B\"ulthoff HH{hhb}{Department Human Perception, Cognition and Action}} } @Inproceedings{ 4597, title = {Perception and prediction of simple object interactions}, year = {2007}, month = {7}, pages = {27-34}, abstract = {For humans, it is useful to be able to visually detect an object's physical properties. One potentially important source of information is the way the object moves and interacts with other objects in the environment. Here, we use computer simulations of a virtual ball bouncing on a horizontal plane to study the correspondence between our ability to estimate the ball's elasticity and to predict its future path. Three experiments were conducted to address (1) perception of the ball's elasticity, (2) interaction with the ball, and (3) prediction of its trajectory. The results suggest that different strategies and information sources are used for passive perception versus actively predicting future behavior.}, file_url = {/fileadmin/user_upload/files/publications/apgv07-27_4597[0].pdf}, web_url = {http://www.apgv.de/}, editor = {Wallraven, C. , V. Sundstedt}, publisher = {ACM Press}, address = {New York, NY, USA}, event_name = {4th Symposium on Applied Perception in Graphics and Visualization (APGV 2007)}, event_place = {Tübingen, Germany}, state = {published}, ISBN = {978-1-59593-670-7}, DOI = {10.1145/1272582.1272587}, author = {Nusseck M{manfred}{Department Human Perception, Cognition and Action}; Lagarde J; Bardy B; Fleming R{roland}{Department Human Perception, Cognition and Action}; B\"ulthoff HH{hhb}{Department Human Perception, Cognition and Action}} } @Inproceedings{ 4467, title = {Perceptual reparameterization of material properties}, year = {2007}, month = {6}, pages = {89-96}, abstract = {The recent increase in both the range and the subtlety of computer graphics techniques has greatly expanded the possibilities for synthesizing images. In many cases, however, the relationship between the parameters of an algorithm and the resulting perceptual effect is not straightforward. Since the ability to produce specific, intended effects is a natural pre-requisite for many scientific and artistic endeavors, this is a strong drawback. Here, we demonstrate a generalized method for determining both the qualitative and quantitative mapping between parameters and perception. Multidimensional Scaling extracts the metric structure of perceived similarity between the objects, as well as the transformation between similarity space and parameter space. Factor analysis of semantic differentials is used to determine the aesthetic structure of the stimulus set. Jointly, the results provide a description of how specific parameter changes can produce specific semantic changes. The method is demonstrated using two datasets. The first dataset consisted of glossy objects, which turned out to have a 2D similarity space and five primary semantic factors. The second dataset, transparent objects, can be described with a non-linear, 1D similarity map and six semantic factors. In both cases, roughly half of the factors represented aesthetic aspects of the stimuli, and half the low-level material properties. Perceptual reparameterization of computer graphics algorithms (such as those dealing with the representation of surface properties) offers the potential to improve their accessibility. This will not only allow easier generation of specific effects, but also enable more intuitive exploration of different image properties.}, web_url = {http://www.eg.org/EG/DL/WS/COMPAESTH/COMPAESTH07}, editor = {Cunningham, D. W., G. W. Meyer, L. Neumann, A. Dunning, R. Paricio}, publisher = {Eurographics Association}, address = {Aire-la-Ville, Switzerland}, booktitle = {Computational Aesthetics 2007}, event_name = {Eurographics Workshop on Computational Aesthetics in Graphics, Visualization and Imaging (CAe '07)}, event_place = {Banff, Alberta, Canada}, state = {published}, ISBN = {978-3-905673-43-2}, DOI = {10.2312/COMPAESTH/COMPAESTH07/089-096}, author = {Cunningham DW{dwc}{Department Human Perception, Cognition and Action}; Wallraven C{walli}{Department Human Perception, Cognition and Action}; Fleming RW{roland}{Department Human Perception, Cognition and Action}; Strasser W} } @Inproceedings{ 4659, title = {Extracting and depicting the 3D shape of specular surfaces}, year = {2005}, month = {8}, pages = {83-86}, abstract = {Many materials including water, plastic and metal have specular surface characteristics. Specular reflections have commonly been considered a nuisance for the recovery of object shape. However, the way that reflections are distorted across the surface depends crucially on 3D curvature, suggesting that they could in fact be a useful source of information. Indeed, observers can have a vivid impression of 3D shape when an object is perfectly mirrored (i.e. the image contains nothing but specular reflections). This leads to the question what are the underlying mechanisms of our visual system to extract this 3D shape information from a perfectly mirrored object. In this paper we propose a biologically motivated recurrent model for the extraction of visual features relevant for the perception of 3D shape information from images of mirrored objects. We analyze qualitatively and quantitatively the results of computational model simulations and show that bidirectional recurrent information processing leads to better results then pure feedforward processing. Furthermore we utilize the model output to create a rough non-photorealistic sketch representation of a mirrored object, which emphasizes image features that are mandatory for 3D shape perception (e.g. occluding contour, regions of high curvature). Moreover, this sketch illustrates that the model generates a representation of object features independent of the surrounding scene reflected in the mirrored object.}, web_url = {http://dl.acm.org/citation.cfm?doid=1080402.1080416}, editor = {Bülthoff, H.H., T. Troscianko}, publisher = {ACM Press}, address = {New York, NY, USA}, event_name = {2nd Symposium on Applied Perception in Graphics and Visualization (APGV 2005)}, event_place = {La Coruña, Spain}, state = {published}, ISBN = {1-59593-139-2}, DOI = {10.1145/1080402.1080416}, author = {Weidenbacher U; Bayerl P; Fleming R{roland}{Department Human Perception, Cognition and Action}; Neumann H} } @Inproceedings{ KhanRFB2005, title = {Image-based material editing}, year = {2005}, month = {8}, pages = {148}, abstract = {Photo editing software allows digital images to be blurred, warped or re-colored. However, it is not currently possible to change the material appearance of an object except by painstakingly painting over the appropriate pixels. We present a set of methods for automatically replacing one material with another material, starting with only a single high dynamic range (HDR) image as input.}, web_url = {https://www.siggraph.org/s2005/}, publisher = {ACM Press}, address = {New York, NY, USA}, booktitle = {ACM SIGGRAPH 2005 Sketches}, event_name = {32nd International Conference and Exhibition on Computer Graphics and Interactive Techniques (SIGGRAPH 2005)}, event_place = {Los Angeles, CA, USA}, state = {published}, DOI = {10.1145/1187112.1187291}, author = {Khan E; Reinhard E; Fleming R{roland}{Department Human Perception, Cognition and Action}; B\"ulthoff HH{hhb}{Department Human Perception, Cognition and Action}} } @Inproceedings{ 2797, title = {Perceiving translucent materials}, year = {2004}, month = {8}, pages = {127-134}, abstract = {Many common materials, including fruit, wax and human skin, are somewhat translucent. What makes an object look translucent or opaque? Here we use a recently developed computer graphics model of subsurface light transport [Jensen, et al., 2001] to study the factors that determine perceived translucency. We discuss how physical factors, such as light-source direction can alter the apparent translucency of an object, finding that objects are perceived to be more translucent when illuminated from behind than in front. We also study the role of a range of image cues, including colour, contrast and blur, in the perception of translucency. Although we learn a lot about images of translucent materials, we find that many simple candidate sources of information fail to predict how translucent an object looks. We suggest that the visual system does not rely solely on these simple image statistics to estimate translucency: the relevant stimulus information remains to be discovered.}, file_url = {/fileadmin/user_upload/files/publications/pdf2797.pdf}, web_url = {http://portal.acm.org/citation.cfm?doid=1012551.1012575}, editor = {Interrante, V. , A. McNamara, H.H. Bülthoff, H.E. Rushmeier}, publisher = {ACM Press}, address = {New York, NY, USA}, event_name = {1st Symposium on Applied Perception in Graphics and Visualization (APGV 2004)}, event_place = {Los Angeles, CA, USA}, state = {published}, ISBN = {1-58113-914-4}, DOI = {10.1145/1012551.1012575}, author = {Fleming R{roland}{Department Human Perception, Cognition and Action}; Jensen HW; B\"ulthoff HH{hhb}{Department Human Perception, Cognition and Action}} } @Inproceedings{ 2562, title = {How do Humans Determine Reflectance Properties under Unknown Illumination?}, year = {2001}, month = {12}, pages = {1-8}, abstract = {Under normal viewing conditions, humans find it easy to distinguish between objects made out of different materials such as plastic, metal, or paper. Untextured materials such as these have different surface reflectance properties, including lightness and gloss. With single isolated images and unknown illumination conditions, the task of estimating surface reflectance is highly underconstrained, because many combinations of reflection and illumination are consistent with a given image. In order to work out how humans estimate surface reflectance properties, we asked subjects to match the appearance of isolated spheres taken out of their original contexts. We found that subjects were able to perform the task accurately and reliably without contextual information to specify the illumination. The spheres were rendered under a variety of artificial illuminations, such as a single point light source, and a number of photographically-captured real-world illuminations from both indoor and outdoor scenes. Subjects performed more accurately for stimuli viewed under real-world patterns of illumination than under artificial illuminations, suggesting that subjects use stored assumptions about the regularities of real-world illuminations to solve the ill-posed problem.}, file_url = {fileadmin/user_upload/files/publications/CVPR-2001-Fleming.pdf}, event_name = {CVPR 2001 Workshop on Identifying Objects Across Variations in Lighting: Psychophysics and Computation}, event_place = {Kauai, HI, USA}, state = {published}, author = {Fleming RW{roland}; Dror RO; Adelson EH} } @Inbook{ 2553, title = {The perceptual organization of depth}, year = {2003}, pages = {1284-1299}, editor = {Chalupa, L. and J. Werner}, publisher = {MIT Press}, address = {Cambridge, MA}, state = {published}, author = {Fleming RW{roland}; Anderson BL} } @Poster{ LiFLK2012, title = {Multi-Stable Visual Motion Perception}, journal = {Frontiers in Computational Neuroscience}, year = {2012}, month = {9}, day = {14}, volume = {Conference Abstract: Bernstein Conference 2012}, pages = {190}, abstract = {Perceptual multi-stability is established when the brain fails to reach a single interpretation of the input from the external world. This issue intrigued scientific minds for more than two hundred years. This phenomenon has been found in vision (Leopold & Logothetis, 1999), audition (Repp, 2007), olfaction (Zhou & Chen, 2009) and speech (Warren & Gregory, 1958). Crucial features are similar within and across modalities (Schwarts et al., 2012). In the visual modality, a number of ambiguous visual patterns have been described such as the Necker cube, motion plaids, and binocular rivalry. Multi-stable stimuli can provide unique insights into visual processing, as changes in perception are decoupled from changes in the stimulus. Understanding of how multi-stable perception occurs might help one to understand visual perception in general. A key question in multi-stable perception is what the brain processes are responsible in the identification and alternation of the percepts. Some investigators suggest that both top-down and bottom-up processes are involved (García Pérez, 1989) but others argue that multi-stable perception does not need high-level processing but happens automatically as low-level competition between the stimulus features (Akman et al., 2009; Wilson et al, 2000). Furthermore, it is well known that changes in stimulus features can bias perception in one or another direction, (Klink, et al., 2012). In order to explore this question, we used multi-stable motion stimuli and specifically moving plaids consisting of three superimposed gratings moving in equidistant directions (difference of 120 deg). These stimuli induce the perception of component and pattern motion simultaneously since any two component gratings bind together and are perceived to move in the opposite direction of the third grating component. We modulated properties of the stimuli such as grating speed and size and recorded the responses of human subjects reporting the direction of the single grating using one of three buttons for each direction. Preliminary results show that perceptual dominance is greatly affected by the selection of grating speeds. Grating size did not greatly change the predominance of the different gratings. We find that gratings with speed closer to physiological values have greater probability to be perceived and that gratings with similar speeds tend to group more often than gratings with different speeds. Further manipulations of other stimulus features like contrast and spatial frequency allow parametric variations of the relative probabilities of different interpretations. Our future goal is to use this information to built models of perceptual alternations using probabilistic inference.}, web_url = {http://www.frontiersin.org/10.3389/conf.fncom.2012.55.00058/event_abstract}, event_name = {Bernstein Conference 2012}, event_place = {München, Germany}, state = {published}, DOI = {10.3389/conf.fncom.2012.55.00058}, author = {Li Q{qinglinli}{Department Physiology of Cognitive Processes}; Fleming RW{roland}{Department Human Perception, Cognition and Action}; Logothetis NK{nikos}{Department Physiology of Cognitive Processes}; Keliris GA{george}{Department Physiology of Cognitive Processes}} } @Poster{ MuryyWF2012, title = {Binocular cues for glossiness}, year = {2012}, month = {5}, day = {22}, pages = {19}, abstract = {The disparity fields created by matte surfaces match the surface's true depth profile. However, for specular surfaces the disparities are shifted away from the surface, tracing out virtual ('antanaclastic') surfaces in depth. Previous studies (Blake & Bülthoff, 1990, Nature, 343, 165; Wendt et al, 2008, doi:10.1167/8.1.14) showed that surfaces appear glossier and more realistic if highlight disparities are physically correct. But which specific binocular cues does the visual system use to identify specularities? We computationally analyzed disparity fields generated by irregularly-shaped objects and found that statistics of vertical disparities (VD) and horizontal disparity gradients (HDG) of specular shapes are qualitatively different from Lambertian surfaces. For specular surfaces, the distributions are heavy-tailed, containing large values that often exceed fusibility limits. This suggests specific binocular cues that the visual system could use for distinguishing glossy and matte materials. In order to test whether these disparity cues affect perceived glossiness, we developed stimuli that allow us to vary disparity fields continuously from perfectly specular to matte and beyond to ‘super glossy’ by varying a single parameter ('virtual IPD'). vIPD parameter defines position of ‘virtual eyes’ on the inter-ocular axis; left and right images are rendered by mapping the illumination on the surface through reflection process due to ‘virtual’ eyes, thus creating left and right virtual reflections while real cameras remain at same positions. We measured gloss discrimination (N = 5) and found that above vIPD = 0.37 human observers perceived stimuli to be as glossy as physically correct mirror stimuli (vIPD=1, ‘virtual eyes’ coincide with real cameras), and below vIPD=0.07 stimuli were perceived as matte as Lambertian (vIPD=0, ‘virtual eyes’ coincide with cyclopean point, left and right reflection patterns are the same). This suggests the brain does not 'know the physics of specular reflection' but instead relies on specific binocular cues.}, web_url = {http://www.theava.net/abstracts/ava2012.pdf}, event_name = {2nd Joint AVA/BMVA Meeting on Biological and Machine Vision}, event_place = {Cambridge, UK}, state = {published}, author = {Muryy AA; Welchman A{aew}{Department Human Perception, Cognition and Action}; Fleming RW{roland}{Department Human Perception, Cognition and Action}} } @Poster{ WelchmanMBF2011, title = {Seeing in 3D: Human psychophysics, modelling and brain imaging}, year = {2011}, month = {5}, day = {26}, abstract = {Successful behaviour relies on reliable estimates of the three-dimensional structure of the environment, facilitating recognition and interaction. Here we review recent work that seeks to understand the neural mechanisms that achieve 3D vision. We focus on the perceptual use of binocular disparity – considering both the computational principles that guide perception and the neural implementation that achieves it. First, we cover work that examines the disparities produced when viewing reflective (specular) objects binocularly. Typically, this produces a considerable discrepancy between the distance specified by disparity (the adanaclastic surface) and the physical surface of the object. We measure perceptual judgements of 3D shape when viewing these shapes, and find that the human visual system tempers its use of disparity signals depending on the structure of the adanaclastic surface. Second, we review neuroimaging work that identifies the neural circuits that process disparity to support depth perception. This work uses high-resolution fMRI combined with machine-learning analysis. In particular, we make parametric stimulus manipulations and test the degree to which different visual areas contain information about the viewed stimulus. This is quantified by the accuracy of a support vector machine in predicting the viewed stimulus from patterns of brain activity. We show that higher portions of both the dorsal and ventral visual pathways process perceptually-relevant disparity signals. However, the type of representation differs between pathways – dorsal responses relate to the metric depth structure, while ventral areas represent depth configurations (sign of depth rather than magnitude).}, web_url = {http://www.theava.net/conf/index.php?conference=Meeting&schedConf=S2011&page=schedConf&op=presentations}, event_name = {AVA/BMVA Spring Meeting 2011 (AGM)}, event_place = {Cardiff, UK}, state = {published}, author = {Welchman A{aew}{Department Human Perception, Cognition and Action}; Muryy A; Ban H; Fleming R{roland}{Department Human Perception, Cognition and Action}} } @Poster{ 6422, title = {Perceived stability of objects changes when the body is tilted relative to gravity}, year = {2010}, month = {6}, volume = {11}, pages = {113}, abstract = {Knowing an object's physical stability affects our expectations about its behaviour and our interactions with it. Objects topple over when the gravity-projected centre-of-mass (COM) lies outside the support area. The critical angle (CA) is the orientation for which an object is perceived to be equally likely to topple over or right itself, which is influenced by global shape information about an object's COM and its orientation relative to gravity. When observers lie on their sides, the perceived direction of gravity is tilted towards the body. Here we test the hypothesis that the CA of falling objects is affected by this internal representation of gravity. Observers sat upright or lay left- or right-side-down, and observed images of objects with different 3D mass distributions that were placed close to the right edge of a table in various orientations. Observers indicated whether the objects were more likely to fall back onto or off the table. The subjective visual vertical was also tested as a measure of perceived gravity. Our results show the CA increases when lying right-side-down and decreases when left-side-down relative to an upright posture, consistent with estimating the stability of rightward falling objects as relative to perceived and not physical gravity.}, web_url = {http://imrf.mcmaster.ca/IMRF/ocs2/index.php/imrf/2010/paper/view/113}, event_name = {11th International Multisensory Research Forum (IMRF 2010)}, event_place = {Liverpool, UK}, state = {published}, author = {Barnett-Cowan M{mbc}{Department Human Perception, Cognition and Action}; Fleming RW{roland}{Department Human Perception, Cognition and Action}; B\"ulthoff HH{hhb}{Department Human Perception, Cognition and Action}} } @Poster{ 5867, title = {Head mobility influences gaze behavior across natural viewing tasks}, journal = {Perception}, year = {2009}, month = {8}, volume = {38}, number = {ECVP Abstract Supplement}, pages = {166}, abstract = {Natural gaze behavior is often studied under conditions that restrain head movements. Here, we report how the availability of head movement can influence gaze behavior on wall-sized images of natural outdoor scenes (field-of- view: ~90°). Participants performed half of the experiment with complete head mobility and the remaining trials with their heads restrained in a chin-rest. They were required to either rate the images for attractiveness (i.e., free-viewing) or to count the visible animals (i.e., visual search). On average, more fixations were found on the trials that allowed for head movements (unrestrained: 4.21 fixations/sec; restrained: 3.75 fixations/sec), which were also shorter in their mean duration (unrestrained: 221 ms; restrained: 252 ms). In addition, unrestrained gaze contained a larger proportion of small amplitude saccades (i.e., less than 5°), than head-restrained gaze. Finally, our participants demonstrated a general preference in fixating regions that were close to the central eye-in-h ead orientation. Altogether, these findings suggest that the availability of head movements allowed our participants to re-orient to regions of interest and sample these regions more frequently. This sampling benefit applied to both visual search and free viewing tasks. The current findings emphasize the importance of allowing head mobility when studying natural gaze behavior.}, web_url = {http://pec.sagepub.com/content/38/1_suppl.toc}, event_name = {32nd European Conference on Visual Perception}, event_place = {Regensburg, Germany}, state = {published}, DOI = {10.1177/03010066090380S101}, author = {Chuang LL{chuang}{Department Human Perception, Cognition and Action}; Herholz S{sherholz}{Department Human Perception, Cognition and Action}; B\"ulthoff HH{hhb}{Department Human Perception, Cognition and Action}; Fleming R{roland}{Department Human Perception, Cognition and Action}} } @Poster{ HoltmannRiceF2009, title = {Shape from smear}, journal = {Perception}, year = {2009}, month = {8}, volume = {38}, number = {ECVP Abstract Supplement}, pages = {28}, abstract = {Recent work indicates that the patterns of scales and orientations in an image ('orientation fields') may play an important role in 3-D shape perception. If true, it should be possible to elicit percepts of specific 3-D shapes using stimuli containing only an appropriate orientation field. To investigate this, we use line-integral convolution to 'smear (coerce) 2-D noise patterns to have a geometrically 'correct' orientation field (ie, as similar as possible to the orientation field present in the rendering of some object). The spatial scales are also modulated to be physically accurate. Importantly, the image generation process is entirely based on 2-D filtering operations, and is fundamentally different from a physically realistic rendering. Despite this, the resulting pattern elicits almost as vivid an impression of the object's 3-D shape as a true rendering. Such images were used in depth comparison and gauge figure tasks to assess the relative contribution of spatial scales and orientation fields to shape perception; as well as the dramatic breakdown of shape perception resulting from physically unrealistic orientation and scale configurations. By examining the accuracy with which subjects are able to make metric judgments (relative depth and surface orientation) about the shape percepts evoked by these patterns, we demonstrate that the continuous variations of orientation and spatial scale across an image can play a key role in 3-D shape inference.}, web_url = {http://pec.sagepub.com/content/38/1_suppl.toc}, event_name = {32nd European Conference on Visual Perception}, event_place = {Regensburg, Germany}, state = {published}, DOI = {10.1177/03010066090380S101}, author = {Holtmann-Rice DN{dhr}{Department Human Perception, Cognition and Action}; Fleming RW{roland}{Department Human Perception, Cognition and Action}} } @Poster{ 4924, title = {Integrated real-time eye, head, and body tracking in front of a wall-sized display}, journal = {Perception}, year = {2007}, month = {8}, volume = {36}, number = {ECVP Abstract Supplement}, pages = {26}, abstract = {Most devices for eye- or gaze-tracking require constrained head and body movements in order to achieve high temporal and spatial accuracy, or a limited field of view or observer positions (eg for keeping the eyes visible for video tracking). This may lead to unnatural viewing conditions, possibly systematically altering gaze patterns in experiments. Furthermore, head and eye movements often cannot be analyzed independently. We present a novel system integrating high-speed eye- and head-tracking, thus enabling observers to move freely in front of large (wall-sized) displays. The system is modular, making it easy to track additional markers for body parts or pointing devices, if desired. Tracking is performed by an Eyelink II (500 Hz) and three Vicon MX motion capture cameras (180 Hz, error&lt;1 mm), respectively. Gaze direction (based on independent eye and head direction) are calculated in real-time (error&lt;0.8°, latency&lt;6 ms), thus al lowing gaze- contingent d isplays. We present possible applications of the system in psychophysics and data visualization.}, web_url = {http://pec.sagepub.com/content/36/1_suppl.toc}, event_name = {30th European Conference on Visual Perception}, event_place = {Arezzo, Italy}, state = {published}, DOI = {10.1177/03010066070360S101}, author = {Canto-Pereira LH{canto}{Department Human Perception, Cognition and Action}; Tanner TG{tanner}{Department Human Perception, Cognition and Action}; Herholz S{sherholz}{Department Human Perception, Cognition and Action}; Fleming RW{roland}{Department Human Perception, Cognition and Action}; B\"ulthoff HH{hhb}{Department Human Perception, Cognition and Action}} } @Poster{ 4883, title = {Lighting Direction Affects Perceived Shape from Shading}, year = {2007}, month = {7}, volume = {10}, pages = {110}, abstract = {It has been known for a long time that many cues contribute to the perception of 3D shape from 2D images, such as shape from shading, textures, occlusions or reflection of the surrounding environment. However, little is known about the influence of lighting conditions on the correct mental reconstruction of 3D shapes. In order to investigate this, we have run a set of experiments asking participants to report differences in surface orientation of unknown, smooth surfaces, using different methods. The first experiment consisted of a 2AFC in which subjects had to identify which of two test objects had the same shape as the target. The stimuli were computer generated irregularly-shaped smooth surfaces, illuminated by a single point light source. For both test stimuli, the position of the light sources could either be different from or the same as the target. Results show that, as the amount of shape difference became smaller, participants were more and more biased towards choosing the match shape lit by the same source as the target. In the second experiment, participants had to report the perceived orientation of the surfaces at various locations by adjusting gauge figures.. The surfaces could either be the same or slightly different and the light source of each shape could either be the same or offset by 90 degrees horizontally. Participants’ matches revealed large differences in perceived surface orientations when the lighting was different, even when the shapes were the same, confirming the first results. Our findings show that lighting conditions can play a substantial role in the perception of 3D structure of objects from their 2D representation. We also discuss the implication of this in the domain of computer aided visualisation.}, web_url = {http://www.twk.tuebingen.mpg.de/twk07/abstract.php?_load_id=caniard01}, event_name = {10th Tübinger Wahrnehmungskonferenz (TWK 2007)}, event_place = {Tübingen, Germany}, state = {published}, author = {Caniard F{franck}{Department Human Perception, Cognition and Action}; Fleming RW{roland}{Department Human Perception, Cognition and Action}} } @Poster{ 4893, title = {Refractive Index and Perceived Transparency}, year = {2007}, month = {7}, volume = {10}, pages = {159}, abstract = {Almost everything that we think we know about the perception of transparent materials is derived from Metelli’s “episcotister model”, or some subtle variant thereof. An opaque disk with a missing wedge is rotated at high-speed (above the flicker-fusion threshold), so that its colour mixes linearly with that of the background. And indeed, we have learnt an immense amount about mid-level vision using this model: it applies well to shadows, specularities, stains, black smoke, gauzes, infinitely thin neutral density filters, or any system that generates the linear superposition of two images. However, ironically, it is hopeless as a model of real chunks of transparent stuff, such as ice cubes, quartz crystals, or even a common glass of water. Most real transparent things (i) have non-zero volume, (ii) obey Fresnel’s equations (and thus exhibit specular reflection and refraction), and consequently (iii) can elicit the vivid impression of transparency without containing any of the cues traditionally thought to be important (e.g. X-junctions or reduction of contrast in the transparent region). Here we report the results of several experiments on the perception of refractive index using physically-based computer simulations of light transport through refractive dielectrics. The first experiments use maximum likelihood difference scaling (MLDS) to measure the perceptual scale of refractive index. We find that the scale is positively bowed for all subjects, which means that smaller refractive indices appear more different from one another than larger refractive indices. The shape of the function is not well predicted by simple measures of imagedifferences. One of the more obvious potential cues is the pattern of distortions created by refraction of the background through a transparent object. We provide a theoretical analysis of this cue, and derive a measure of the pattern of distortions that the visual system could plausibly perform, called the ‘distortion field’. The distortion field, D = div(d), where d is the field of vectors measuring the spatial displacement of features caused by refraction through the object. Although the distortion field varies systematically with refractive index, it is also affected by the object shape, the distance to the background, and the distance to the viewer, so it is an ambiguous cue. In a set of matching experiments, we find that observers make large systematic errors in the estimation of refractive index when these irrelevant scene factors are varied, suggesting that subjects are unable to overcome this ambiguity.}, web_url = {http://www.twk.tuebingen.mpg.de/twk07/abstract.php?_load_id=fleming01}, event_name = {10th Tübinger Wahrnehmungskonferenz (TWK 2007)}, event_place = {Tübingen, Germany}, state = {published}, author = {Fleming RW{roland}{Department Human Perception, Cognition and Action}} } @Poster{ 4923, title = {Eye movements for active learning of objects}, journal = {Journal of Vision}, year = {2007}, month = {6}, volume = {7}, number = {9}, pages = {22}, abstract = {We investigated how humans use eye movements to direct their attention to informative features in a categorization task. More specifically, we test the hypothesis that eye movements are influenced by prior knowledge about a task and by information gathered in previous fixations. Our novel stimuli, which belonged to either one of two probabilistic classes, were large circular contours with several regular perturbations at which the curvature was varied as a continous feature dimension. With this design the spatial separation of single features generally required several closer fixations to make a confident decision about class membership. Each feature value varied stochastically from trial to trial according to a characteristic distribution for each category (external noise). The features were independent and varied in diagnosticity. Subjects had to learn the categories by using immediate feedback about the true category after each trial (4 subjects, 10 sessions of 250 trials). We estimated the internal noise, which was much smaller then the external noise, based on an independent experiment measuring curvature discrimination performance for different eccentricites (0–12°), finding approx. linear decrease in sensitivity with increasing curvature. The subjects were able to learn to discriminate the categories (avg. performance for ideal observer vs. subjects was 0.82 vs 0.68). Trial by trial fluctations in performance follow the ideal observer (MAE 0.32). With increasing expertise reaction times became shorter and fixations became more focused, possibly reflecting the subjects' belief about relevant features. We compare the results with Bayesian learner models which take into account the peripheral fall-off in discriminability, while directing their attention to the currently most informative features.}, web_url = {http://www.journalofvision.org/7/9/22/}, event_name = {7th Annual Meeting of the Vision Sciences Society (VSS 2007)}, event_place = {Sarasota, FL, USA}, state = {published}, DOI = {10.1167/7.9.22}, author = {Tanner TG{tanner}{Department Human Perception, Cognition and Action}; Fleming R{roland}{Department Human Perception, Cognition and Action}; B\"ulthoff HH{hhb}{Department Human Perception, Cognition and Action}} } @Poster{ 4835, title = {Manifesto for the Study of Material Perception}, year = {2006}, month = {3}, volume = {9}, pages = {93}, abstract = {When we look at everyday things, we not only perceive their 3D shape and identity, but also we generally enjoy a distinct visual impression of their material properties. Without touching an object, we can usually tell at a glance whether it is soggy or dry, soft or hard, smooth or rough. How does the visual system recognize materials? What are the major challenges that the visual system faces? Despite the enormous variety and vividness of material perception, it is only just beginning to emerge as a major topic of study in vision research [e.g. 1–7]. Here I present a framework for understanding human visual perception of materials and introduce a number of novel demonstrations of our visual aptitude for estimating material properties. The main thesis I will present is that despite our exquisite sensitivity to changes in physical states (e.g. subtle changes in appearance allow us to tell the difference between fresh and stale bread) the visual system does not generally estimate the intrinsic physical attributes of materials (e.g. density or coefficient of viscosity). Instead, it adopts a heuristic strategy for classifying material appearance based on the statistical behaviour of materials in our environment. In the real world, the observed appearance of a material is subject to constraints such as gravity and natural illumination conditions. Consequently, there exists a large set of simple low-level image measurements (e.g. contrast distributions, amplitude spectra, optic flow patterns, etc.) that reliably correlate with changes in physical state. I will present a taxonomy that organizes these cues, and embed all extant research on material perception within this framework. Broadly I organize the cues into three classes: (1) optical cues, i.e., information arising from the manner in which a material interacts with light, such as its specular reflectance, or sub-surface scattering coefficients. This class of cues has received the most attention, as there is a considerable body of work on the estimation of diffuse albedo and colour. (2) geometric cues, i.e., the characteristic 3D shapes adopted by a material subject to natural forces. (3) dynamic cues, i.e., the way that a material tends to change shape over time or interact with other objects in the scene. I use a variety of physics-based computer graphics simulations to demonstrate these cues and their low-level correlates. Finally I show circumstances under which high-level (cognitive) factors can influence our perception of materials.}, web_url = {http://www.twk.tuebingen.mpg.de/twk06/abstract.php?_load_id=fleming01}, event_name = {9th Tübingen Perception Conference (TWK 2006)}, event_place = {Tübingen, Germany}, state = {published}, author = {Fleming RW{roland}{Department Human Perception, Cognition and Action}} } @Poster{ 3591, title = {Orientation fields in the perception of 3D shape}, journal = {Journal of Vision}, year = {2005}, month = {9}, volume = {5}, number = {8}, pages = {525}, abstract = {If you pick up a typical textbook on perception you'll learn that there are many cues to 3D shape, such as texture, shading, highlights, perspective, etc. Each of these sources of information has a different physical cause. Thus, to interpret each cue, the visual system must impose a different set of computational constraints. This has lead to the widely held belief that each 3D shape cue is processed by a separate, dedicated processing stream or ‘module’. A considerable amount of research has gone into working out how accurate shape estimates can be derived from each cue, and how these independent estimates can be combined optimally. However, surprisingly little work has been done to try and find commonalities between the various cues. Here we show theoretically how shape from shading, highlights, texture, perspective and possibly even stereo can share some common processing tricks. The key insight is that the projection of 3D surfaces into 2D images introduces dramatic local image anisotropies that depend directly on properties of the 3D shape. Globally, these anisotropies are organized into smooth, continuous, swirling patterns, which we call ‘orientation fields’. We have argued recently (Fleming, et al. JOV 4(9), 2004) that orientation fields can be used to recover shape from specularities. Here we show how orientation fields could play a role in a wider range of cues. For example, although diffuse shading looks completely unlike mirror reflections, in both cases there is a systematic mapping from 3D surface curvatures to 2D image gradients. Thus, both shading and specularities lead to similar orientation fields. The mapping from orientation fields to 3D shape is different for other cues, and we exploit this to create powerful illusions. We also show how some simple image-processing tricks could allow the visual system to ‘translate’ between cues. Finally, we outline the remaining problems that have to be solved to develop a ‘unified theory’ of 3D shape recovery.}, web_url = {http://journalofvision.org/5/8/525/}, event_name = {Fifth Annual Meeting of the Vision Sciences Society (VSS 2005)}, event_place = {Sarasota, FL, USA}, state = {published}, DOI = {10.1167/5.8.525}, author = {Fleming R{roland}{Department Human Perception, Cognition and Action}; B\"ulthoff H{hhb}{Department Human Perception, Cognition and Action}} } @Poster{ WeidenbacherBFN2005_2, title = {Perception of mirrored objects: A modeling approach}, journal = {Perception}, year = {2005}, month = {8}, volume = {34}, number = {ECVP Abstract Supplement}, pages = {177}, abstract = {When we look at a polished metal kettle we get a remarkably strong impression of its 3-D shape. The question what are the underlying mechanisms to recover the shape of a mirrored object from a single static image (eg a photograph) remains. In general, this task is ill-posed since infinitely many possible combinations of the illumination pattern from the surrounding scene and surface properties can generate the same image. Here, we present a biologically motivated model for analysing images of mirrored objects to recover 3-D geometric shape properties. In order to constrain the space of possible solutions, we assume that the reflected scene contains isotropic contrast information. When the scene is isotropic, the distortions of the reflected image are related to the surface curvature of the object (second derivatives of the surface function) (Fleming et al, 2004 Journal of Vision 4 798 - 820). First, we use orientation-selective Gabor filters (V1 cells) to extract the raw orientation and strength of the local distortions that are caused by the mirrored surface. Next, we pool context information from the vector field of orientations (inspired by V2 cells with long-range lateral connections) and use this as a feedback signal (Neumann and Sepp, 1999 Biological Cybernetics 81 425 - 444). The recurrent feedforward/feedback loop enhances and smooths the flow patterns of image orientations to recover the characteristic curvature properties. Our simulations demonstrate quantitatively that the model can reliably extract surface curvature information even when the reflected scene is not isotropic (ie the model can withstand violations of the basic assumptions). Our investigations thus provide a simple, neurally inspired mechanism for the representation and processing of mirrored objects by the visual system.}, web_url = {http://pec.sagepub.com/content/34/1_suppl.toc}, event_name = {28th European Conference on Visual Perception}, event_place = {A Coruña, Spain}, state = {published}, DOI = {10.1177/03010066050340S101}, author = {Weidenbacher R; Bayerl P; Fleming R{roland}{Department Human Perception, Cognition and Action}; Neumann H} } @Poster{ 3646, title = {Abstraction of physical properties from complex object interactions: the case of elasticity}, year = {2005}, month = {2}, volume = {8}, pages = {135}, abstract = {For humans it is useful to be able to visually infer an object’s physical properties (e.g. weight, hardness or elasticity). One potentially important source of information is the way that an object moves and interacts with other objects in the environment. For example, the way that a ball bounces could inform us about its elasticity. There have been several explorations of what are the necessary and typical visual cues in a bouncing event. However, in most previous work the stimuli consisted of a ball bouncing repeatedly on a simple horizontal plane. Warren, Kim and Husney (1987) showed that under these circumstances, there are at least three heuristic cues to elasticity: relative height, relative period and relative velocity of the bounces. We wanted to test whether the visual system can interpret more complex bouncing events in which these simple cues are not present in the display. Can subjects abstract something more sophisticated from the trajectories of bouncing objects, or must they rely on these simple heuristics? To test this, we used the Virtools Physics Pack to simulate a ball falling through an array of horizontal cylindrical pegs housed in a vertical box. The ball fell from a random location above the box, bounced a number of times and finally fell out of a hole at the bottom. This stimulus allows us to completely randomize the duration that the ball needs to get through this box, the number of collisions, the velocity of the ball and the height of the rebounds, because the angle of the collisions with the pegs is always different. Subjects performed an elasticity matching task. Subjects were presented with two pegboxes simultaneously. The left-hand box was the Test ball, whose elasticity was chosen at random by the computer. The right-hand box contained the Match ball, whose elasticity could be adjusted by the subject. The subject?s task was to adjust this elasticity of the Match ball until it appeared to have the same behavior as the Test ball. The results show that subjects generally performed poorly in this task, despite dramatic variations in the elasticity of the ball. However, we found large individual differences, in which some subjects were able to perform the task above chance levels. Our results suggest that subjects normally rely on simple heuristics to estimate elasticity (e.g. bounce height), which, by design, were eliminated from our stimuli. Further research is needed to investigate which additional, complex cues were used in some cases to abstract the behaviour of the ball.}, web_url = {http://www.twk.tuebingen.mpg.de/twk05/programm.php}, event_name = {8th Tübingen Perception Conference (TWK 2005)}, event_place = {Tübingen, Germany}, state = {published}, author = {Nusseck M{manfred}{Department Human Perception, Cognition and Action}; Fleming R{roland}{Department Human Perception, Cognition and Action}; B\"ulthoff HH{hhb}{Department Human Perception, Cognition and Action}} } @Poster{ WeidenbacherBFN2005, title = {Mechanisms of Recovering Shape Properties from Perfectly Mirrored Objects}, year = {2005}, month = {2}, volume = {8}, pages = {139}, abstract = {When we look at a perfectly mirrored object, such as a polished kettle, we generally have a remarkably strong impression of its 3D shape. This leads to the question of whether there is a mechanism to completely recover the shape of a mirrored object from a single static image (e.g. a photograph). Without explicit knowledge of the surrounding scene, this is theoretically impossible because many possible combinations of illumination from the surrounding scene and surface properties can generate the same image (i.e. it is an ill-posed problem). Therefore, the only way to extract information about object shape is to constrain the possible combinations of object shape and illumination. If we assume that the reflected scene contains isotropic contrast information, then there is a close relation between the surface curvature of an object (specifically the second derivatives of the surface function) and the distortions of the reflected scenery [1]. In this contribution we present two different computational methods for analysing images of mirrored objects to recover certain properties of 3D shape. Our first method is a statistical approach, based on principal components of the image gradient computed in a local neighborhood, known as the structure tensor. In this context, the eigenvectors of the tensor tell us the orientation of curvature and the eigenvalues of the tensor give us information about the anisotropy of curvature (ratio of maximal and minimal curvature). Our second method is a biologically motivated approach, based on Gabor filters and grouping. We apply an iterative refinement in a simple model of cortical feedforward/feedback processing [2]. Context information is collected by cells with long-range lateral connections. This information is fed back to enhance regions where local information matches the top-down reentry pattern provided by the larger context. Our approach shows that under the assumption mentioned above, it is possible to recover two characteristic curvature properties of mirrored objects: (i) the direction of maximal and minimal curvature and (ii) the anisotropy of curvature. Our simulations demonstrate that both methods (the statistical and biological motivated approach) lead to comparable results and that the models perform well even if the assumption of isotropic contrasts in the scenery is violated to a certain degree.}, web_url = {http://www.twk.tuebingen.mpg.de/twk05/programm.php}, event_name = {8th Tübingen Perception Conference (TWK 2005)}, event_place = {Tübingen, Germany}, state = {published}, author = {Weidenbacher U; Bayerl P; Fleming R{roland}{Department Human Perception, Cognition and Action}; Neumann H} } @Poster{ Fleming2005, title = {On the Visual Perception of Translucent Materials}, year = {2005}, month = {2}, volume = {8}, pages = {89}, abstract = {Many commonly occurring substances are somewhat translucent (e.g. wax, jade, fruit-flesh, and cheese). When light strikes a translucent material, it passes through the surface and scatters a number of times within the body of the object before re-emerging. This causes light to ‘bleed’ through translucent objects, giving them a distinctive visual softness and glow. What image cues are responsible for this characteristic appearance? How do we distinguish between translucent and opaque materials? Here we use a combination of image statistics and psychophysics to study the perception of translucent materials. There has been a large amount of previous work on the perception of materials that transmit light. Almost all of this work is based on simple physical models of transparency, (e.g. the episcotister model of Metelli, 1974), in which the object of interest is a thin filter or screen. However, recent advances in computer graphics (Jensen et al. 2001; Jensen and Buhler, 2002) make it possible to simulate the complex physics of solid translucent objects. We have used this model to study how a wide range of factors influence the perception of translucency, including highlights, colour, contrast, brightness, blurriness, and conditions of illumination. Our main findings are as follows: (1) We have found that it is possible to enjoy a vivid impression of translucency even when many of the cues that were traditionally believed to be important for the perception of transparency (e.g. X-Junctions, contrast conditions) are absent from the display. (2) We argue that sub-surface light scattering is too complex for the visual system to infer translucency by inverse optics. Accordingly we suggest that the visual system tracks low-level image statistics that reliably correlate with changes in translucency. (3)We find that perceived translucency varies dramatically with conditions of illumination. We compare how well a number of candidate cues can predict these variations. In conclusion, there is a wide range of materials that have not been studied before, and which we are only just beginning to understand. Many intuitions that we have about which cues are crucial for recovering opacity turn out to be at best incomplete.}, web_url = {http://www.twk.tuebingen.mpg.de/twk05/programm.php}, event_name = {8th Tübingen Perception Conference (TWK 2005)}, event_place = {Tübingen, Germany}, state = {published}, author = {Fleming R{roland}{Department Human Perception, Cognition and Action}} } @Poster{ 2796, title = {Perceiving Translucent Materials}, journal = {Journal of Vision}, year = {2004}, month = {8}, volume = {4}, number = {8}, pages = {119}, abstract = {Many materials — such as wax, glass, fruit flesh, and human skin — transmit as well as reflect light. When light passes through an object, it gives the object a characteristic appearance of transparency or translucency. How do we identify materials that transmit light? What are the perceptual dimensions of translucency? What image properties make an object look transmissive rather than opaque? We use a combination of ecological optics and psychophysics to address these questions. Almost all research on the perception of transmissive materials is based on Metelli's linear ‘episcotister’ model. Unfortunately, the episcotister is a poor physical model of light transport in real materials. It ignores: (i) specular reflection, (ii) surface ‘frosting’ (as in ‘frosted’ glass), (iii) refraction and (iv) sub-surface scatter. These shortcomings have profound consequences for the perception of translucency. They affect both the perceptual parameters of transparent materials and the image properties that make objects look transmissive. Recent advances in computer graphics (Jensen et al. SIGGRAPH, 2001) allow us to simulate translucent materials realistically. We can now systematically vary sub-surface light scatter, while holding shape, lighting and viewpoint constant. This allows us to identify image properties that are diagnostic of translucency. We discuss how image statistics based on luminance, contrast, orientation, and scale contribute to the perception of translucency, as well as other cues such as highlights and shadows. Using psychophysical matching tasks, we measure how refractive index and translucency appear to change as the object or lights are moved. Importantly, we find that traditional cues to transparency (e.g. X-junctions and visibility of the underlying layer) are not necessary, and in fact rarely occur in realistic images of transparent objects. Indeed, subjects can estimate an object's translucency even when it is floating in a featureless void.}, web_url = {http://www.journalofvision.org/content/4/8/119.abstract}, event_name = {Fourth Annual Meeting of the Vision Sciences Society (VSS 2004)}, event_place = {Sarasota, FL, USA}, state = {published}, DOI = {10.1167/4.8.119}, author = {Fleming RW{roland}{Department Human Perception, Cognition and Action}; Adelson EH; B\"ulthoff HH{hhb}{Department Human Perception, Cognition and Action}; Jensen HW} } @Poster{ 2561, title = {Orientation fields in the perception of 3D shape and material properties}, year = {2004}, month = {2}, volume = {7}, pages = {164}, abstract = {I present a theoretical analysis that explains how the visual system could solve two key perceptual problems. The rst problem is our ability to distinguish reections from texture markings. The second problem is the estimation of 3D object shape from monocular images. Textures and reections both lead to stochastic patterns in images. How can we tell them apart? We have argued previously [1] that textures and reections have different statistical properties (e.g. specular reections of the real world have heavily skewed pixel histograms). However, there is an additional cue, which results from the way that patterns are distorted by 3D shape. As a textured plane is oriented away from frontoparallel, the image of the texture becomes compressed. This provides a cue for 3D shape: if the visual system can measure the compression of the texture at each image location, it can recover the rst derivative of the surface (i.e. local orientation) and thus shape. I argue that specular reections can be treated a bit like textures, because they also lead to stochastic image patterns with well-conserved statistics. When the world is reected in a specular surface, the reection is distorted by the shape of the object. The pattern of distortion is a function of the 3D shape, just as it is with textures. Crucially, however, for specularities the compression is a function of the second rather than the rst derivative of the surface (i.e. surface curvature as well as orientation). Hence, the mapping from image compression to 3D shape follows different rules for specular vs. textured surfaces. I show that the compressions produced by 3D curvatures reliably lead to characteristic `elds' of orientation energy across the image of a specular surface. These orientation elds are diagnostic of 3D shape but remain surprisingly stable across changes in the scene reected in the surface. Furthermore, I show that these characteristic orientation elds can be easily extracted from the image by populations of linear lters that resemble the oriented receptive elds of V1 cells. I show how orientation elds could allow the visual system to distinguish between reections and textures, even when they are present simultaneously. Finally, I discuss the generalization of these principles to surfaces with arbitrary reectance properties.}, web_url = {http://www.twk.tuebingen.mpg.de/twk04/index.php}, event_name = {7th Tübingen Perception Conference (TWK 2004)}, event_place = {Tübingen, Germany}, state = {published}, author = {Fleming RW{roland}{Department Human Perception, Cognition and Action}} } @Poster{ 2560, title = {How image statistics drive shape-from-texture and shape-from-specularity}, journal = {Journal of Vision}, year = {2003}, month = {10}, volume = {3}, number = {9}, pages = {73}, abstract = {We present a new visual cue that allows the visual system to solve two key perceptual problems under a large range of circumstances. The first problem is our ability to distinguish specular reflections from texture markings. The second problem is the estimation of 3D object shape from monocular images. Textures and specular reflections both lead to stochastic patterns in images. How can we tell them apart? Recently we have argued that textures and reflections have different statistical properties (e.g. specular reflections of the real world have heavily skewed pixel histograms). However, there is an additional cue, which results from the way that patterns are distorted by 3D shape. As a textured plane is oriented away from frontoparallel, the image of the texture becomes compressed. This provides a cue for 3D shape: if the visual system can measure the compression of the texture at each image location, it can recover local orientation and thus shape. We argue that specular reflections can be treated a bit like textures, because they also lead to stochastic image patterns with well-conserved statistics. When the world is reflected in a specular surface, the reflection is distorted by the shape of the object. The pattern of distortion is a function of the 3D shape, just as it is with textures. Crucially, however, for specularities the compression is a function of surface curvature as well as orientation. Hence, the mapping from image compression to 3D shape follows different rules for specular vs. textured surfaces. We call the pattern of compressions across an image the ‘texture trajectory’. Texture trajectories can allow the visual system to distinguish specular reflections from textures, and to estimate 3D shape for both textured and specular objects. The texture trajectory cue is weakest for spheres and planes, and strongest for objects with very different surface curvatures in orthogonal directions (e.g. cylinders). We exploit this to generate some powerful demos.}, web_url = {http://journalofvision.org/3/9/73/}, event_name = {Third Annual Meeting of the Vision Sciences Society (VSS 2003)}, event_place = {Sarasota, FL, USA}, state = {published}, DOI = {10.1167/3.9.73}, author = {Fleming RW{roland}; Torralba A; Dror RO; Adelson EH} } @Poster{ 2559, title = {Resolving figure-ground ambiguity}, journal = {Journal of Vision}, year = {2002}, month = {11}, volume = {2}, number = {7}, pages = {90}, abstract = {Recent theoretical work (Anderson, VSS 2001) has shown that occlusion geometry introduces an asymmetry in the depth relationships that can be inferred from near versus far contrast signals. Here, we show how this analysis predicts that the figure-ground relationships of a contour can be resolved by manipulating the depth of a few 3D dots. Methods: We used two paradigms to assess the encoding of contours in ambiguous figure-ground displays. In Experiment 1, subjects were presented with a rectangle divided into light and dark halves by an irregular contour. Their task was to recall the shape of the dividing contour. A second screen contained either the left or the right half of the rectangle. Subjects indicated whether the irregular contour of the second shape was the same as in the first screen. Perceived border ownership in the 1st screen was manipulated with a few (2 or 6) dots; disparity either placed the dots behind, or in front of, the other half of the display. In Experiment 2 subjects observed similar displays and reported which side appeared as figure, and which as ground. Results: When the dots were in front of the dividing contour, there was little effect on subjective judgments of figure-ground in Experiment 2, or the reaction times of Experiment 1. This implies that relatively near features (dots) do not uniquely specify the border ownership of further edges. However, when subjects were tested with the half that had contained dots more distant than the contour, reaction times were slowed. In this configuration, the far dots “capture” the regions surrounding the dots to a depth behind the contour, which resolves the border ownership of the contour. Conclusions: There is an inherent asymmetry in the ability of relatively near and far depth signals to resolve border ownership. We will discuss how the failure to appreciate this difference between near and far depth signals on border ownership has led to erroneous claims about figure-ground perception.}, web_url = {http://journalofvision.org/2/7/90/}, event_name = {Second Annual Meeting of the Vision Sciences Society (VSS 2002)}, event_place = {Sarasota, FL, USA}, state = {published}, DOI = {10.1167/2.7.90}, author = {Fleming RW{roland}; Williams A; Anderson BL} } @Poster{ 2557, title = {Surface reflectance estimation under unknown natural illumination}, journal = {Journal of Vision}, year = {2001}, month = {12}, volume = {1}, number = {3}, pages = {43}, abstract = {Purpose : Physical surfaces such as metal, plastic, or paper have different optical qualities that lead to different characteristics in images. The actual image of a surface, however, depends heavily on the illumination. This experiment measures the accuracy with which humans match surfaces of similar reflectance properties under different natural illuminations, in the absence of contextual information to specify illumination. Methods : A set of balls were computer rendered as if illuminated by 9 real-world 360° illumination maps, taken from Debevec et al. (2000). The balls' reflectance properties were parameterized using Pellacini et al.'s (2000) psychophysically uniform reparameterization of the Ward reflectance model. A range of values determined the magnitude of the specular lobe, c, and the sharpness of the specular lobe, d. Subjects were presented with 2 balls of randomly selected c and d values rendered with different illumination maps. They then had to adjust c and d for one of the balls (the ‘match’) until its perceived reflectance qualities were the same as for the other ball (the ‘test’). All balls were viewed against a black background, in the absence of contextual information. Results : Correlation and regression analyses reveal that subjects perform accurately and reliably for both c (slope=0.83; correlation coefficient=0.79) and d (slope=0.90; correlation coefficient=0.90). Furthermore they performed significantly better than with a set of contrast-polarity inverted images derived from the original set, which produce no coherent percept of surface reflectance but which contain spatially identical image properties (p<0.05). Conclusions : Contextual information is not required for reliable matches of material qualities.}, web_url = {http://journalofvision/1/3/43}, event_name = {First Annual Meeting of the Vision Sciences Society (VSS 2001)}, event_place = {Sarasota, FL, USA}, state = {published}, DOI = {10.1167/1.3.43}, author = {Fleming RW{roland}; Dror RO; Adelson EH} } @Thesis{ 2556, title = {Human visual perception under real-world illumination}, year = {2004}, state = {published}, type = {PhD}, author = {Fleming RW{roland}} } @Conference{ 6405, title = {Perceived object stability is affected by the internal representation of gravity}, journal = {Perception}, year = {2010}, month = {8}, volume = {39}, number = {ECVP Abstract Supplement}, pages = {109}, abstract = {Knowing an object's physical stability affects our expectations about its behaviour and our interactions with it. Objects topple over when the gravity-projected centre-of-mass (COM) lies outside the support area. The critical angle (CA) is the orientation for which an object is perceived to be equally likely to topple over or right itself, which is influenced by global shape information about an object's COM and its orientation relative to gravity. When observers lie on their sides, the perceived direction of gravity is tilted towards the body. Here we test the hypothesis that the CA of falling objects is affected by this internal representation of gravity. Observers sat upright or lay left- or right-side-down, and observed images of objects with different 3D mass distributions that were placed close to the right edge of a table in various orientations. Observers indicated whether the objects were more likely to fall back onto or off the table. The subjective visual vertical was also tested as a measure of perceived gravity. Our results show the CA increases when lying right-side-down and decreases when left-side-down relative to an upright posture, consistent with estimating the stability of rightward falling objects as relative to perceived and not physical gravity.}, web_url = {http://pec.sagepub.com/content/39/1_suppl.toc}, event_name = {33rd European Conference on Visual Perception}, event_place = {Lausanne, Switzerland}, state = {published}, DOI = {10.1177/03010066100390S101}, author = {Fleming RW{roland}{Department Human Perception, Cognition and Action}; Barnett-Cowan M{mbc}{Department Human Perception, Cognition and Action}; B\"ulthoff HH{hhb}{Department Human Perception, Cognition and Action}} } @Conference{ 5726, title = {Shape and Stuff}, year = {2009}, month = {6}, web_url = {http://www.cvr.yorku.ca/conferences/cvr2009/index.html}, event_name = {International Conference on Vision in 3D Environments (CVR 2009)}, event_place = {Toronto, Canada}, state = {published}, author = {Fleming RW{roland}{Department Human Perception, Cognition and Action}} } @Conference{ 5855, title = {Visual Perception of the Physical Properties of Objects}, year = {2009}, month = {4}, day = {7}, abstract = {Whenever we look at an object, we effortlessly perceive a wide range of its physical properties. We don‘t just recognize objects, we also mentally "size them up", tacitly asking ourselves: what is it made of?, how can it be used?, where should I hold it if I want to pick it up?, how big is it?, how stable? and so on. In this talk, I will present research on the human visual estimation of the physical properties of objects. I‘ll talk about how we estimate surface properties such as glossiness and translucency, and outline some important future directions for research into the perception of material properties. I‘ll also talk about the perception of 3D curvatures and how estimates of shape might be put to good use in inferring other properties of objects. Although the emphasis will be on the problems as they are usually posed by psychology and neuroscience, I will also try to make some connections to other disciplines for which perception is relevant, such as computer graphics and design.}, web_url = {https://www.tudelft.nl/live/pagina.jsp?id=8fe4dafd-e8e2-46cf-937e-57e42ed9b23d&lang=en}, event_name = {Industrial Design Department Colloquium, TU Delft}, event_place = {Delft, Netherlands}, state = {published}, author = {Fleming RW{roland}{Department Human Perception, Cognition and Action}} } @Conference{ 5724, title = {Visual perception of materials that transmit light}, year = {2008}, month = {10}, day = {17}, web_url = {http://color.psych.upenn.edu/workshop08/}, event_name = {Workshop on Perception of Material Properties in 3D Scenes}, event_place = {Philadelphia, PA, USA}, state = {published}, author = {Fleming RW{roland}{Department Human Perception, Cognition and Action}} } @Conference{ Fleming2008, title = {Predicting successes and failures of 3-D shape estimation}, journal = {Perception}, year = {2008}, month = {8}, volume = {37}, number = {ECVP Abstract Supplement}, pages = {89}, abstract = {Humans are generally pretty good at visually estimating the 3-D shape of objects. However, under some circumstances we are subject to illusions. For example, in 'shape from shading', certain illumination conditions can systematically alter perceived 3-D shape. Similarly, in 'shape from texture', certain textures can induce systematic misperceptions of shape. Most computational theories of 'shape-from-x' focus on achieving accurate shape reconstruction. However, a good model of human vision, should account for the pattern or errors as well as successes. Here, in a series of gauge-figure and similarity rating tasks, we measure how perceived shape changes across variations in illumination, surface reflectance, texture, and certain shape transformations. We then show how a number of simple image statistics derived from filters tuned to different orientations and scales qualitatively predict the pattern of both successes and errors. Importantly, this shows how both similarities and differences between cues (such as shading, highlights, and texture) might be explained by a common front-end.}, web_url = {http://pec.sagepub.com/content/37/1_suppl.toc}, event_name = {31st European Conference on Visual Perception}, event_place = {Utrecht, Netherlands}, state = {published}, DOI = {10.1177/03010066080370S101}, author = {Fleming RW{roland}{Department Human Perception, Cognition and Action}} } @Conference{ Fleming2008_2, title = {Towards a unified theory of 3D shape perception}, journal = {International Journal of Psychology}, year = {2008}, month = {7}, day = {23}, volume = {43}, number = {3-4}, pages = {426}, abstract = {Objectives. Unifying theoretical analysis of visual 3D shape cues, including texture, shading and highlights. Experiments test whether we experience illusions of shape predicted by the model. Methods. Model uses the population response of filters tuned to different image orientations (cf. V1 cells). Subjects viewed rendered images of 3D objects and adjusted ’gauge figure’ probes to report perceived surface orientation. Results: Model cor- rectly predicts both success and failures of human 3D shape estimation across variations in texture, lighting and surface reflectance properties. Conclu- sions: For the early stages of 3D shape estimation, seemingly different cues may have more in common than previously believed.}, web_url = {http://www.mrcbndu.ox.ac.uk/sites/default/files/pdf_files/Optimal%20decision%20making%20in%20the%20cortico-basalganglia.pdf}, event_name = {XXIX. International Congress of Psychology (ICP 2008)}, event_place = {Berlin, Germany}, state = {published}, DOI = {10.1080/00207594.2008.10108485}, author = {Fleming R{roland}{Department Human Perception, Cognition and Action}} } @Conference{ FlemingLA2008, title = {Image statistics for 3D shape estimation}, journal = {Journal of Vision}, year = {2008}, month = {6}, volume = {8}, number = {6}, pages = {76}, abstract = {Most accounts of ‘Shape-from-X’ start with a computational theory of a particular cue, then outline methods for extracting relevant data from the image. Here we take the opposite approach, starting with image statistics and investigating how they might be exploited to estimate shape across variations in lighting, reflectance and texture. We rendered a large number objects and looked for image statistics that vary systematically with properties of the shape. We find several simple measurements — derived from filters at different orientations and scales — yield surprisingly reliable information about 3D shape. In a series of experiments we show that changes in these statistics predict certain successes and failures of human perception. In a gauge probe task, shape perception remained remarkably constant across changes in surface reflectance (glossiness, albedo). Although the images differ substantially on a pixel-by-pixel basis, the orientation statistics remain stable across these reflectance changes, suggesting they could be the basis of human performance. In another task, observers were presented with shaded objects that had been subjected to certain shape transformations. The task was to adjust the magnitude of shear or stretch of a textured object until it appeared to be the same shape as the shaded object. Subjects underestimate the shear transformation for shaded objects, and the scaling transformation for textured objects, consistent with the predictions derived from our image statistics analysis. Thus, differences between cues may be predicted by a common front end. In another task, we applied transformations to texture and shading that elicit illusions of 3D shape. The strength of the illusions correlates with the induced changes in the orientation and scale statistics. Together, these findings suggest that to understand 3D shape perception, it is useful to reformulate the problem in terms of the image measurements made by the front end of vision.}, web_url = {http://jov.arvojournals.org/article.aspx?articleid=2137493}, event_name = {8th Annual Meeting of the Vision Sciences Society (VSS 2008)}, event_place = {Naples, FL, USA}, state = {published}, DOI = {10.1167/8.6.76}, author = {Fleming R{roland}{Department Human Perception, Cognition and Action}; Li Y; Adelson E} } @Conference{ 5722, title = {Perception of Materials that Transmit Light}, year = {2008}, month = {5}, day = {9}, abstract = {Many materials that we commonly encounter, such as ice, marmalade and wax, transmit some proportion of incident light. Broadly, these can be separated into transparent and translucent materials. Transparent materials (e.g. gemstones, water) are dominated by specular reflection and refraction, leading to a characteristic glistening, pellucid appearance. Translucent materials (e.g. marble, cheese) exhibit sub-surface light scattering, in which light bleeds diffusely through the object creating a distinctive soft or glowing appearance. Importantly, both types of material are poorly approximated by Metelli’s episcotister or other models of thin neutral density filters that have shaped our understanding of transparency to date. I will present various psychophysical and theoretical studies that we have performed using physically based computer simulations of light transport through solid transmissive objects. One important observations is that these materials do not exhibit many image features traditionally thought to be central to transparency perception (e.g. X-junctions). However, they compensate with a host of novel cues, which I will describe. I will discuss the perceptual scales of refractive index and translucency and report systematic failures of constancy across changes in illumination, 3D shape and context. I will discuss conditions under which various low-level image statistics succeed and fail to predict material appearance. I will also discuss the difficulties posed by transmissive materials for the estimation of 3D shape. Under many conditions, human vision appears to use simple image heuristics rather than correctly inverting the physics. I will show how this can be exploited to create illusions of material appearance.}, web_url = {http://slideplayer.com/slide/2624949/}, event_name = {8th Annual Meeting of the Vision Sciences Society (VSS 2008): Symposium on "Surface Material Perception"}, event_place = {Naples, FL, USA}, state = {published}, author = {Fleming R{roland}{Department Human Perception, Cognition and Action}} } @Conference{ 5721, title = {Human Visual Perception of 3D Shape}, year = {2008}, month = {2}, event_name = {Departmental Colloquium, Max Planck Institute for Biological Cybernetics}, event_place = {Tübingen, Germany}, state = {published}, author = {Fleming RW{roland}{Department Human Perception, Cognition and Action}} } @Conference{ Fleming2007, title = {Towards a general theory of 3D shape perception}, year = {2007}, month = {10}, day = {3}, abstract = {Estimating the 3D shape of objects in our environment is one of the most fundamental problems in visual perception, yet it is still rather poorly understood. If you pick up a typical vision text, you'll learn there are many cues to 3D shape, such as shading, texture gradients and specular highlights. A considerable amount of work has studied each cue in isolation and also how various cues can be combined optimally. However, relatively little research has attempted to find commonalities between cues. Here I will argue that a number of seemingly different 3D shape cues could share some common processing strategies. The key insight is that when patterns such as shading or texture are projected from a 3D object into the 2D retinal image, the patterns are systematically distorted in a way that has easily-measurable effects on the local image statistics. The distortions create clearly organized patterns of local image orientation ('orientation fields') that are systematically related to properties of the 3D shape. These orientation fields can be reliably detected by populations of simple filters tuned to different image orientations, as found in V1. I will outline some of the computational benefits of using orientation fields to estimate 3D shape and show through demonstrations and illusions how they can predict both successes and failures of human 3D shape perception. Together these findings suggest that orientation fields could serve as a powerful, 'common currency' for the first stages of 3D shape estimation.}, web_url = {http://minneapolis.eventful.com/events/roland-fleming-towardsageneraltheoryof3dshap-/E0-001-006534924-4}, event_name = {University of Minnesota}, event_place = {Minneapolis, MN, USA}, state = {published}, author = {Fleming R{roland}{Department Human Perception, Cognition and Action}} } @Conference{ 5719, title = {Visual Perception of Surface Materials}, year = {2007}, month = {10}, day = {1}, abstract = {Different materials such as silk, bronze and marmalade have distinctive visual appearances. Human observers are remarkably adept at recognizing materials across a wide range of viewing conditions and we are only just beginning to work out how. What gives a material its characteristic 'look'? What cues does the visual system use to identify materials? How can we leverage the assumptions made by the visual system to improve computer graphics? I will review some of our research on the perception of material properties such as gloss, translucency and refractive index that attempts to shed some light on these questions. Ill talk about how illumination and 3D geometry interact with material perception, and discuss the role of various image statistics (e.g. intensity histogram, amplitude spectrum) in the visual estimation of material attributes. Ill then show one application in which we exploit the heuristics made by the visual system to enable illusory modifications of material appearance in photographs.}, web_url = {http://www.jaloxa.eu/mirrors/radiance_workshops/2007/index.html}, event_name = {6th International Radiance and HDR Scientific Workshop}, event_place = {Minneapolis, MN, USA}, state = {published}, author = {Fleming RW{roland}{Department Human Perception, Cognition and Action}} } @Conference{ 5720, title = {Towards a Unified Theory of 3D Shape Perception}, year = {2007}, month = {10}, event_name = {Departmental Colloquium: Max Planck Institute for Biological Cybernetics}, event_place = {Tübingen, Germany}, state = {published}, author = {Fleming RW{roland}{Department Human Perception, Cognition and Action}} } @Conference{ 4927, title = {Real-time gaze-tracking for freely-moving observers}, journal = {Journal of Eye Movement Research}, year = {2007}, month = {8}, volume = {1}, number = {5}, pages = {37}, abstract = {We have developed a real-time mobile gaze-tracker, by combining a high-speed eye-tracker (Eyelink II, 500Hz) with head- and body-tracking (VICON, 200Hz). The position of the observer’s gaze on the screen can be measured continuously with an accuracy of <1.0 deg as they walk around and make head movements in a natural way. The system is modular, i.e. individual components can be easily replaced (e.g., different eye and head tracking systems can be used). The system is primarily developed for interaction in front of wall-sized displays. For validation, the system has been tested with displays of different sizes (from 2.2x1.8m to 5.2x2.5m), and several applications, including psychophysical experiments and a multiresolution gaze-contingent display.}, file_url = {fileadmin/user_upload/files/publications/ECEM-2007-Herholz.pdf}, web_url = {https://bop.unibe.ch/index.php/JEMR/article/view/2251/3447}, event_name = {14th European Conference on Eye Movements (ECEM 2007)}, event_place = {Potsdam, Germany}, state = {published}, DOI = {10.16910/jemr.1.5.1}, author = {Herholz S{sherholz}{Department Human Perception, Cognition and Action}; Tanner TG{tanner}{Department Human Perception, Cognition and Action}; Canto-Pereira LH{canto}{Department Human Perception, Cognition and Action}; Fleming RW{roland}{Department Human Perception, Cognition and Action}; B\"ulthoff HH{hhb}{Department Human Perception, Cognition and Action}} } @Conference{ FlemingJM2007, title = {Visual perception of refractive materials}, journal = {Journal of Vision}, year = {2007}, month = {6}, volume = {7}, number = {9}, pages = {561}, web_url = {http://www.journalofvision.org/content/7/9/561}, event_name = {7th Annual Meeting of the Vision Sciences Society (VSS 2007)}, event_place = {Sarasota, FL, USA}, state = {published}, DOI = {10.1167/7.9.561}, author = {Fleming R{roland}{Department Human Perception, Cognition and Action}; J\"akel F{frank}{Department Empirical Inference}; Maloney L{ltm}} } @Conference{ 5718, title = {Human Visual Perception}, year = {2006}, month = {9}, event_name = {HDR-Photography and Reality Based Visualization}, event_place = {Hamburg, Germany}, state = {published}, author = {Fleming RW{roland}{Department Human Perception, Cognition and Action}} } @Conference{ 5717, title = {Image Based Material Editing}, year = {2006}, month = {6}, event_name = {Departmental Colloquium}, event_place = {Tübingen, Germany}, state = {published}, author = {Fleming RW{roland}{Department Human Perception, Cognition and Action}} } @Conference{ FlemingB2005, title = {Fourier cues to 3-D shape}, journal = {Perception}, year = {2005}, month = {8}, volume = {34}, number = {ECVP Abstract Supplement}, pages = {53}, abstract = {If you pick up a typical vision text, you'll learn there are many cues to 3-D shape, such as shading, linear perspective, and texture gradients. Much work has been done to study each cue in isolation and also how the various cues can be combined optimally. However, relatively little work has been devoted to finding commonalities between cues. Here, we present theoretical work that demonstrates how shape from shading, texture, highlights, perspective, and possibly even stereopsis could share some common processing strategies. The key insight is that the projection of a 3-D object into a 2-D image introduces dramatic distortions into the local image statistics. It does not matter much whether the patterns on a surface are due to shading, specular reflections, or texture: when projected into the image, the resulting distortions reliably cause anisotropies in the local Fourier spectrum. Globally, these anisotropies are organised into smooth, coherent patterns, which we call 'orientation fields'. We have argued recently [Fleming et al, 2004 Journal of Vision 4(9) 798 - 820] that orientation fields can be used to recover shape from specularities. Here we show how orientation fields could play a role in a wider range of cues. For example, although diffuse shading looks completely unlike mirror reflections, in both cases image intensity depends on 3-D surface orientation. Consequently, derivatives of surface orientation (curvature) are related to derivatives of image intensity (intensity gradients). This means that both shading and specularities lead to similar orientation fields. The mapping from orientation fields to 3-D shape is different for other cues, and we exploit this to create powerful illusions. We also show how some simple image-processing tricks could allow the visual system to 'translate' between cues. Finally, we outline the remaining problems that have to be solved to develop a 'unified theory' of 3-D shape recovery.}, web_url = {http://pec.sagepub.com/content/34/1_suppl.toc}, event_name = {28th European Conference on Visual Perception}, event_place = {A Coruña, Spain}, state = {published}, DOI = {10.1177/03010066050340S101}, author = {Fleming RW{roland}{Department Human Perception, Cognition and Action}; B\"ulthoff HH{hhb}{Department Human Perception, Cognition and Action}} } @Conference{ 5731, title = {Perception of Translucent Materials}, year = {2004}, month = {12}, event_name = {Universität Bonn, Department of Computer Science, Colloquium}, state = {published}, author = {Fleming RW{roland}{Department Human Perception, Cognition and Action}} } @Conference{ 5730, title = {Natural Sheen Statistics}, year = {2003}, month = {10}, event_name = {Workshop on the Perception of Object Color and Material Properties in Three Dimensional Scenes}, event_place = {New York, NY, USA}, state = {published}, author = {Fleming RW{roland}{Department Human Perception, Cognition and Action}} } @Conference{ 5728, title = {Specularities in the Perception of Glossiness and 3D Shape}, year = {2003}, month = {4}, event_name = {Harvard Vision Group Seminar Series}, event_place = {Camridge, MA, USA}, state = {published}, author = {Fleming RW{roland}{Department Human Perception, Cognition and Action}} } @Conference{ 5729, title = {Specularities, Illumination and Perception}, year = {2003}, month = {4}, event_name = {MIT Artificial Intelligence Laboratory Group Meeting}, event_place = {Stanford, CA, USA}, state = {published}, author = {Fleming RW{roland}{Department Human Perception, Cognition and Action}} } @Conference{ 5727, title = {Real world illumination and the perception of surface gloss}, year = {2003}, month = {2}, event_name = {NTT Communication Science Laboratories Group Meeting}, event_place = {Atsugi, Japan}, state = {published}, author = {Fleming RW{roland}{Department Human Perception, Cognition and Action}} }