Time/Room: Friday, May 13, 2016, 12:00 – 2:00 pm, Talk Room 1-2
Organizer(s): Peter Scarfe, Dept. Psychology, University of Reading, UK
Presenters: Tony Movshon, David Brainard, Roland Fleming, Johannes Burge, Jenny Read, Wendy Adams

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Symposium Description

The symposium will focus on the fine balance that all experimenters have to strike between adopting artifice or realism as an experimental methodology. As scientists, should we use stimuli and tasks that are extremely well characterized, but often bare little resemblance to anything someone would experience outside of an experiment? Or should we use realistic stimuli and tasks, but by doing so sacrifice some level of experimental control? How do we make valid inferences about brain and behavior based upon each approach, and is there a deal be struck, where we gain the best of both worlds? The symposium will bring together leading researchers who have taken differing approaches to satisfying the needs of realism and artifice. These will include those who have used artificial, or indeed physically impossible, stimuli to probe both 2D and 3D perception; those who have pioneered the use of photo-realistically rendered stimuli in experiments, and developed the tools for other experimenters to do so; and others who combine measurement of natural images statistics from the real world, with well characterized artificial stimuli during experiments. The research presented will cover perception and action in humans, non-human primates, and insects. Techniques will span both behavioral experiments as well as neurophysiology. All speakers will discuss the pros and cons of their approach and how they feel the best balance can be struck between ecological validity and experimental control. The symposium will be relevant to anyone attending VSS, whether student, postdoc, or faculty. In terms of benefits gained, we want to both inspire those at the start of their career, as well as provoke those with established research programs to consider alternative approaches. The aim is to give the audience an insight into how best to design experiments to make valid inferences about brain and behavior. The scientific merit of this is clear; at whatever stage of our research career, we as scientists should constantly be questioning our beliefs about the validity of our research with respect to the real world. The topic of the symposium is highly original and has never been more timely. With existing technology, it is possible to simulate parametrically-controlled photo-realistic stimuli that cannot be distinguished from real photographs. We can also map the statistics of the world around us in exquisite detail. Combine this with the prospect of affordable virtual reality in the near future, running highly-realistic experiments has never been easier. Despite this, the vast majority of experiments still use very artificial stimuli and tasks. It is only by defining and debating what we mean by “realism” and “artifice” that we will understand if this is a problem, and whether a fundamental shift is needed for us to truly understand the brain.

Presentations

Using artifice to understand nature

Speaker: Tony Movshon, NYU

Vision evolved to function in the natural world, but that does not mean that we need to use images of that world to study vision. Synthetic stimuli designed to test hypotheses about visual encoding and representation (e.g. lines, edges, gratings, random dot kinematograms and stereograms, textures with controlled statistics have given us a clear picture of many specific visual mechanisms, and allow principled tests of theories of visual function. What more could a reasonable person want?

The use of graphics simulations in the study of object color appearance

Speaker: David Brainard; University of Pennsylvania
Additional Authors: Ana Radonjić, Department of Psychology, University of Pennsylvania

A central goal in the study of color appearance is to develop and validate models that predict object color appearance from a physical scene description. Ultimately, we seek models that apply for any stimulus, and particularly for stimuli typical of natural viewing. One approach is to study color appearance using real illuminated objects in quasi-natural arrangements. This approach has the advantage that the measurements are likely to capture what happens for natural viewing. It has the disadvantage that it is challenging to manipulate the stimuli parametrically in theoretically interesting ways. At the other extreme, one can choose simplified stimulus sets (e.g., spots of light on uniform backgrounds, or ‘Mondrian’ configurations). This approach has the advantage that complete characterization of performance within the set may be possible, and one can hope that any principles developed will have general applicability. On the other hand, there is no a priori guarantee that what is learned will indeed be helpful for predicting what happens for real illuminated objects. Here we consider an intermediate choice, the use of physically-accurate graphics simulations. These offer the opportunity for precise stimulus specification and control; particularly interesting is the ability to manipulate explicitly distal (object and illuminant) rather than proximal (image) stimulus properties. They also allow for systematic introduction of complexities typical of natural stimuli, thus making it possible to ask what features of natural viewing affect performance and providing the potential to bridge between the study of simplified stimuli and the study of real illuminated objects.

Confessions of a reluctant photorealist

Speaker: Roland Fleming, Dept. of Experimental Psychology, University of Giessen

For some scientific questions, highly reduced stimuli are king. Sine waves. Gabors. Points of light. When paired with rigorous theory, such stimuli provide scalpel-like tools of unparalleled precision for dissecting sensory mechanisms. However, even the most disciplined mind is wont at times to turn to questions of subjective visual appearance. Questions like ‘what makes silk look soft?’, ‘why does honey look runny?‘ or ‘how can I tell wax is translucent?’. In order to study such complex phenomena (fluid flow, subsurface scattering, etc.), there simply is no alternative to using ‘real’ or ‘photorealistic’ stimuli, as these remain the only extant stimuli that elicit the relevant percepts. I will briefly describe a couple of my own experiments using computer simulations of complex physical processes to study the visual appearance of materials and the underlying visual computations. I will discuss both boons and perils of using computer simulations to study perception. On the one hand, the phenomena are horrendously complex and we still lack experimental methods for bridging the gap between discrimination and subjective appearance. On the other hand, simulations provide an unprecedented level of parametric control over complex processes, as well as access to the ground truth state of the scene (shape, motion, ray paths, etc). Finally, I will argue that using and analysing simulations is a necessary step in the development of more focussed, reduced stimuli that will also evoke the requisite phenomenology: one day we may have the equivalent of Gabors for studying complex visual appearance.

Predicting human performance in fundamental visual tasks with natural stimuli

Speaker: Johannes Burge, Department of Psychology, Neuroscience Graduate Group, University of Pennsylvania

Understanding how vision works under natural conditions is a fundamental goal of vision science. Vision research has made enormous progress toward this goal by probing visual function with artificial stimuli. However, evidence is mounting that artificial stimuli may not be fully up to the task. The field is full of computational models—from retina to behavior—that beautifully account for performance with artificial stimuli, but that generalize poorly to arbitrary natural stimuli. On the other hand, research with natural stimuli is often criticized on the grounds that natural signals are too complex and insufficiently controlled for results to be interpretable. I will describe recent efforts to develop methods for using natural stimuli without sacrificing computational and experimental rigor. Specifically, I will discuss how we use natural stimuli, techniques for dimensionality reduction, and ideal observer analysis to tightly predict human estimation and discrimination performance in three tasks related to depth perception: binocular disparity estimation, speed estimation, and motion through depth estimation. Interestingly, the optimal processing rules for processing natural stimuli also predict human performance with classic artificial stimuli. We conclude that properly controlled studies with natural stimuli can complement studies with artificial stimuli, perhaps contributing insights that more traditional approaches cannot.

Natural behaviour with artificial stimuli: probing praying mantis vision

Speaker: Jenny Read; Newcastle University, Institute of Neuroscience
Additional Authors: Dr Vivek Nityananda, Dr Ghaith Tarawneh, Dr Ronny Rosner, Ms Lisa Jones, Newcastle University, Institute of Neuroscience

My lab is working to uncover the neural circuitry supporting stereoscopic vision in the praying mantis, the only invertebrate known to possess this ability. Mantises catch their prey by striking out with their spiked forelimbs. This strike is released only when prey is perceived to be at the appropriate distance, so provides an extremely convenient way of probing the insects’ depth perception. Other behaviours, such as tracking, saccades and optomotor response, also inform us about mantis vision. Because we are using natural rather than trained behaviours, our stimuli have to be naturalistic enough to elicit these responses. Yet as we begin the study of mantis stereopsis, clear answers to our scientific questions are often best obtained by artificial or indeed impossible stimuli. For example, using artificial “cyclopean” stimuli, where objects are defined purely by disparity, would enable us to be sure that the mantis’ responses are mediated totally by disparity and not by other cues. Using anti-correlated stereograms, which never occur in nature, could help us understand whether mantis stereopsis uses cross-correlation between the two eyes’ images. Accordingly, my lab is navigating a compromise between these extremes. We are seeking stimuli which are naturalistic enough to drive natural behaviour, while artificial enough to provide cleanly-interpretible answers our research questions – although we do sometimes end up with stimuli which are naturalistic enough to present confounds, and artificial enough to lack ecological validity. I will discuss the pros and cons, and aim to convince you we are making progress despite the pitfalls.

Natural scene statistics and estimation of shape and reflectance.

Speaker: Wendy Adams; University of Southampton
Additional Authors: Erich W. Graf, University of Southampton, Southampton, UK; James H. Elder, York University, Canada

A major function of the visual system is to estimate the shape and reflectance of objects and surfaces from the image. Evidence from both human and computer vision suggests that solutions to this problem involve exploiting prior probability distributions over shape, reflectance and illumination. In an optimal system, these priors would reflect the statistics of our world. To allow a better understanding of the statistics of our environment, and how these statistics shape human perception, we have developed the Southampton-York Natural Scenes (SYNS) public dataset. The dataset includes scene samples from a wide variety of indoor and outdoor scene categories. Each scene sample consists of (i) 3D laser range (LiDAR) data over a nearly spherical field of view, co-registered with (ii) spherical high dynamic range imagery, and (iii) a panorama of stereo image pairs. These data are publicly available at https://syns.soton.ac.uk/. I will discuss a number of challenges that we have addressed in the course of this project, including: 1) geographic sampling strategy, 2) scale selection for surface analysis, 3) relating scene measurements to human perception. I will also discuss future work and potential applications.

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Artifice versus realism as an experimental methodology

Organizer(s): Peter Scarfe, Department of Psychology, University of Reading, UK
Time/Room: Friday, May 13, 2016, 12:00 – 2:00 pm, Talk Room 1-2

How do we make valid inferences about brain and behavior based on experiments using stimuli and tasks that are extremely well characterized, but bare little resemblance to the real world? Is this even a problem? This symposium will bring together leading researchers who have taken differing approaches to striking a balance between the experimental control of “artifice” and the ecological validity of “realism”. The aim is to provoke debate about how best to study perception and action, and ask whether a fundamental shift is needed for us to truly understand the brain. More…

Boundaries in Spatial Navigation and Visual Scene Perception

Organizer(s): Soojin Park, Johns Hopkins University and Sang Ah Lee, University of Trento
Time/Room: Friday, May 13, 2016, 12:00 – 2:00 pm, Pavilion

Humans and nonhuman animals compute locations in navigation and scene perception by using a spontaneously encoded geometry of the 3D environmental boundary layouts. The aim of this symposium is to bridge research from various subfields to discuss the specific role of boundaries in the processing of spatial information and to converge on a coherent theoretical framework for studying visual representations of boundaries. To achieve this, our interdisciplinary group of speakers will discuss research on a broad range of subject populations, from rodents, to primates, to individuals with genetic disorders, using various experimental methods (developmental, behavioral, fMRI, TMS, single-cell and population coding). More…

What do deep neural networks tell us about biological vision?

Organizer(s): Radoslaw Martin Cichy, Department of Psychology and Education, Free University Berlin, Berlin, Germany
Time/Room: Friday, May 13, 2016, 2:30 – 4:30 pm, Talk Room 1-2

To understand visual cognition we ultimately need an explicit and predictive model of neural processing. In recent years deep neural networks—brain-inspired computer vision models—have emerged as a promising model for visual capacities in the neurosciences. This symposium delivers the first results regarding how DNNs help us to understand visual processing in the human brain and provides a forum for critical discussion of DNNs: what have we gained, what are we missing, and what are the next steps? More…

What can we learn from #TheDress – in search for an explanation

Organizer(s): Annette Werner, Institute for Ophthalmic Research, Tübingen University
Time/Room: Friday, May 13, 2016, 2:30 – 4:30 pm, Pavilion

Few topics in colour research have generated so much interest in the science community and public alike, as the recent phenomenon #TheDress. The Symposium shall gather the actual experimental evidence and provide a profound basis for a discussion and evaluation of the hypotheses regarding the origin of the phenomenon. Furthermore, #TheDress is a chance for further insight into the nature of human colour perception, in particular with respect to individual differences, and cognitive influences, including memory, colour preferences and the interaction between peception and language. More…

ARVO@VSS: Information processing in a simple network: What the humble retina tells the brain.

Organizer(s): Scott Nawy, PhD, University of Nebraska Medical Center and Anthony Norcia, Stanford University
Time/Room: Friday, May 13, 2016, 5:00 – 7:00 pm, Talk Room 1-2

This year’s biennial ARVO at VSS symposium features a selection of recent work on circuit-level analyses of retinal, thalamic and collicular systems that are relevant to understanding of cortical mechanisms of vision. The speakers deploy a range of state-of-the art methods that bring an unprecedented level of precision to dissecting these important visual circuits. More…

The parietal cortex in vision, cognition, and action

Organizer(s): Yaoda Xu, Harvard University and David Freedman, University of Chicago
Time/Room: Friday, May 13, 2016, 5:00 – 7:00 pm, Pavilion

The parietal cortex has been associated with a diverse set of functions, such as visual spatial processing, attention, motor planning, object representation, short-term memory, categorization and decision making. By bringing together researchers from monkey neurophysiology and human brain imaging, this symposium will integrate recent findings to update our current understanding of the role of parietal cortex in vision, cognition and action. By bridging different experimental approaches and diverse perceptual, cognitive, and motor functions, this symposium will also attempt to address whether it is possible to form a unified view of parietal functions. More…

Friday, May 15, 2015, 9:00 – 11:30 am, Island Ballroom

Dave Knill was a beloved scientist, teacher, and VSS regular who suddenly passed away in 2014. Dave also served on the VSS Board of Directors from 2002 to 2007. Dave got his Ph.D. from Brown University in 1990 with a thesis about the perception of surface shape and reflectance. He did a postdoc at the University of Minnesota, after which he held faculty positions at the University of Pennsylvania and the University of Rochester, where he was since 1999. Dave left a towering legacy in many areas of vision science and decision-making, from Bayesian modeling to spatial vision to active sensing to multisensory perception to bounded rationality. In this symposium, a few of Dave’s many trainees and collaborators will commemorate his life and work.

Speakers: Dan Kersten, Paul Schrater, Robert Jacobs, Chris Sims, Krystel Huxlin, Wei Ji Ma

View Introduction

Dan Kersten

Bayesian vision: The early years   View Slides, View Video

By the mid 1980s, computer science had helped to define vision problems to be solved, but had also shown how elusive their solutions could be. Neurophysiology was showing that primate visual processing involved significantly more cortex than had been thought. Marr’s book had just been published and understanding human vision was starting to look like a bigger and more interesting challenge. Around the same time, advances in digital signal processing were providing the means to create, filter and manipulate images. 3D computer graphics was making it possible to generate images from models of objects and scenes. Signal detection theory had been widely used for several decades, but most applications to studies of human vision had involved image patterns as the signals. This was the state of affairs when David Knill began his graduate work at Brown University. In my talk, I will describe the enormous role David played over the subsequent ten years in developing our understanding of objects and scenes as signals, images as their causal results, and from there, perception as Bayesian inference.

Paul Schrater

Perception for action   View Slides, View Video

Cue integration formed a critical problem when I was Dave’s graduate student and formed one of Dave’s research foci throughout his career. I will describe Dave’s key contributions to the conceptualization of cues, Bayesian approaches and methods for elicitation. As we both moved to visuomotor control, we began to reconceptualize cue integration from a control perspective. I will trace that history and describe its deep influence on more recent work where we challenge  the idea of cues as information towards privileged variables like object shape, size or location, and instead develop the idea that integrating perceptual information should subserve the goals of action. In effect, what you are doing determines what information is relevant, which variables should be estimated, and how perceptual input relates to the variables needed to make control decisions. I’ll review Dave’s innovative approaches to assessing cue integration, from slant from texture to visual signals to hand location. I’ll also describe a cue integration experiment where subjects successfully learned to integrate visual and auditory cues in non-standard ways in order to control an object. Throughout, Dave’s pioneering use of probabilistic modeling for conceptual development, stimulus design and data analysis will be highlighted.

Robert Jacobs

Theoretical approaches to multisensory perception   View Slides, View Video

I will start by describing research that was generated by Dave’s scientific creativity, rigor, and passion. This research, conducted by Joseph Atkins, Dave, and me, examined how inconsistent sensory signals in a multisensory (visual-haptic) environment can lead people to recalibrate how they combine depth information from multiple visual cues. I will then review subsequent research from my lab on crossmodal transfer of object shape knowledge across visual and haptic modalities, as well as work on transfer of knowledge from a perception task to a motor production task. Dave and I were both interested in sensory integration, multisensory perception, and possible relationships between perception and motor production. Talking with Dave about all of these topics was great fun and often insightful.

Chris Sims

Bounded rationality   View Slides, View Video

Dave Knill wasn’t content to observe or measure human behavior, he wanted to explain it. To Dave, an explanation for behavior and brain function almost always consisted of its elegant and parsimonious restatement as the solution to a computational problem. During the time I spent in his lab, I focused on two projects: Understanding the adaptive allocation of visual gaze in complex tasks (an offshoot of his work in visual-motor control with Jeff Saunders), and redefining visual working memory as the problem of minimizing behavioral costs under a capacity constraint (building on his work with Anne-Marie Brouwer). This latter project advanced information theory as a principled approach to defining the limits of visual working memory. In hindsight, both projects are really about bounded rationality—computational explorations of the idea that the brain can be highly limited, and yet simultaneously efficient. Dave was selfless as a mentor, and I am honored to have had the chance to grow as a scientist working in his laboratory.

Krystel Huxlin

Impact of vision lost and regained on direction of heading estimates from optic flow   View Slides, View Video

Understanding this was the goal of the research Dave and I were pursuing with our graduate student, Laurel Issen. Dave passed away before this goal could be fully realized but it illustrates his openness and willingness to apply rigorous approaches to the study of clinical problems. I will start by explaining why our original question was (and still remains) of interest in the context of cortically blind people. My lab studies how visual training restores some of the vision lost in this patient population. It was of great interest for Dave and me to better understand why the cortically blind, who retain at least one intact hemifield of vision in both eyes, have such trouble navigating and orienting in their environment. Answering this question represents a first step in assessing whether restoring some of the vision lost is likely to impact visually-guided functions and ultimately, quality of life in this patient population.

Wei Ji Ma

Mixture priors and causal inference   View Slides, View Video

Although Dave was one of the humblest people you would ever meet, the theoretical and empirical contributions he made to perception research are second to none. I will highlight mixture priors and causal inference, two intertwined computational concepts related to the inference of hidden causes. In a seminal 2003 paper on depth perception, he introduced the concept of mixture priors in vision. He later studied visuo-memory cue combination in a naturalistic reaching task with Anne-Marie Brouwer. In 2008, I worked on an extension of this study with him, in which we explored causal inference in the same reaching task. Very recently, Dave and Oh-Sang Kwon used the same notion of causal inference to explain how the brain resolves conflicts between local and global motion cues. Dave was a dear friend, an amazingly selfless and patient mentor, and one of the best scientists I have known.

Organizers: Thomas Naselaris & Kendrick Kay; Department of Neurosciences, Medical University of South Carolina & Department of Psychology, Washington University in St. Louis
Presenters: Thomas Naselaris, Marcel van Gerven, Kendrick Kay, Jeremy Freeman, Nikolaus Kriegeskorte, James J. DiCarlo, MD, PhD

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Symposium Description

Central to visual neuroscience is the problem of representation: what features of the visual world drive activity in different areas of the visual system? Receptive fields and tuning functions have long served as the basic descriptive elements used to characterize visual representations. In recent years, the receptive field and the tuning function have been generalized and in some cases replaced with alternative methods for characterizing visual representation. These include decoding and multivariate pattern analysis, representational similarity analysis, the use of abstract semantic spaces, and models of stimulus statistics. Given the diversity of approaches, it is important to consider whether these approaches are simply pragmatic, driven by the nature of the data being collected, or whether these approaches might represent fundamentally new ways of characterizing visual representations. In this symposium, invitees will present recent discoveries in visual representation, explaining the generality of their approach and how it might be applicable to future studies. Invitees are encouraged to discuss the theoretical underpinnings of their approach and its criterion for “success”. Invitees are also encouraged to provide practical pointers, e.g. regarding stimulus selection, experimental design, and data analysis. Through this forum we hope to move towards an integrative approach that can be shared across experimental paradigms. Audience: This symposium will appeal to researchers interested in computational approaches to understanding the visual system. The symposium is expected to draw interest from a broad range of experimental backgrounds (e.g. fMRI, EEG, ECoG, electrophysiology). Invitees: The invitees will consist of investigators who have conducted pioneering work in computational approaches to studying visual representation.

Presentations

Visual representation in the absence of retinal input

Speaker: Thomas Naselaris; Department of Neurosciences, Medical University of South Carolina, Charleston, SC

An important discovery of the last two decades is that receptive fields in early visual cortex provide an efficient basis for generating images that have the statistical structure of natural scenes. This discovery has lent impetus to the theory that receptive fields in early visual cortex can function not only as passive filters of retinal input, but as mechanisms for generating accurate representations of the visual environment that are independent of retinal input. A number of theoretical studies argued that such internal visual representations could play an important functional role in vision by supporting probabilistic inference. In this talk, we will explore the idea of receptive fields as generators of internal representations by examining the role that receptive fields play in generating mental images. Mental images are the canonical form of internal visual representation: they are independent of retinal input and appear to be essential for many forms of inference. We present evidence from fMRI studies that voxel-wise receptive field models of the tuning to retinotopic location, orientation, and spatial frequency can account for much of the BOLD response in early visual cortex to imagining previously memorized works of art. We will discuss the implications of this finding for the structure of functional feedback projections to early visual cortex, and for the development of brain-machine interfaces that are driven by mental imagery.

Learning and comparison of visual feature representations

Speaker: Marcel van Gerven; Donders Institute for Brain, Cognition and Behaviour

Recent developments on the encoding and decoding of visual stimuli have relied on different feature representations such as pixel-level, Gabor wavelet or semantic representations. In previous work, we showed that high-quality reconstructions of images can be obtained via the analytical inversion of regularized linear models operating on individual pixels. However, such simple models do not account for the complex nonlinear transformations of sensory input that take place in the visual hierarchy. I will argue that these nonlinear transformations can be estimated independent of brain data using statistical approaches. Decoding based on the resulting feature space is shown to yield better results than those obtained using a hand-designed feature space based on Gabor wavelets. I will discuss how alternative feature spaces that are either learned or hand-designed can be compared with one another, thereby providing insight into what visual information is represented where in the brain. Finally, I will present some recent encoding and decoding results obtained using ultra-high field MRI.

Identifying the nonlinearities used in extrastriate cortex

Speaker: Kendrick Kay; Department of Psychology, Washington University in St. Louis

In this talk, I will discuss recent work in which I used fMRI measurements to develop models of how images are represented in human visual cortex. These models consist of specific linear and nonlinear computations and predict BOLD responses to a wide range of stimuli. The results highlight the importance of certain nonlinearities (e.g. compressive spatial summation, second-order contrast) in explaining responses in extrastriate areas. I will describe important choices made in the development of the approach regarding stimulus design, experimental design, and analysis. Furthermore, I will emphasize (and show through examples) that understanding representation requires a dual focus on abstraction and specificity. To grasp complex systems, it is necessary to develop computational concepts, language, and intuition that can be applied independently of data (abstraction). On the other hand, a model risks irrelevance unless it is carefully quantified, implemented, and systematically validated on experimental data (specificity).

Carving up the ventral stream with controlled naturalistic stimuli

Speaker: Jeremy Freeman; HHMI Janelia Farm Research Campus
Authors: Corey M. Ziemba, J. Anthony Movshon, Eero P. Simoncelli, and David J. Heeger Center for Neural Science New York University, New York, NY

The visual areas of the primate cerebral cortex provide distinct representations of the visual world, each with a distinct function and topographic representation. Neurons in primary visual cortex respond selectively to orientation and spatial frequency, whereas neurons in inferotemporal and lateral occipital areas respond selectively to complex objects. But the areas in between, in particular V2 and V4, have been more difficult to differentiate on functional grounds. Bottom-up receptive field mapping is ineffective because these neurons respond poorly to artificial stimuli, and top-down approaches that employ the selection of “interesting” stimuli suffer from the curse of dimensionality and the arbitrariness of the stimulus ensemble. I will describe an alternative approach, in which we use the statistics of natural texture images and computational principles of hierarchical coding to generate controlled, but naturalistic stimuli, and then use these images as targeted experimental stimuli in electrophysiological and fMRI experiments. Responses to such “naturalistic” stimuli reliably differentiate neurons in area V2 from those in V1, in both single-units recorded from macaque monkey, and in humans as measured using fMRI. In humans, responses to these stimuli, alongside responses to both simpler and more complex stimuli, suggest a simple functional account of the visual cortical cascade: Whereas V1 encodes basic spectral properties, V2, V3, and to some extent V4 represent the higher-order statistics of textures. Downstream areas capture the kinds of global structures that are unique to images of natural scenes and objects.

Vision as transformation of representational geometry

Speaker: Nikolaus Kriegeskorte; Medical Research Council, Cognition and Brain Sciences Unit, Cambridge, UK

Vision can be understood as the transformation of representational geometry from one visual area to the next, and across time, as recurrent dynamics converge within a single area. The geometry of a representation can be usefully characterized by a representational distance matrix computed by comparing the patterns of brain activity elicited a set of visual stimuli. This approach enables to compare representations between brain areas, between different latencies after stimulus onset, between different individuals and between brains and computational models. I will present results from human functional imaging of early and ventral-stream visual representations. Results from fMRI suggest that the early visual image representation is transformed into an object representation that emphasizes behaviorally important categorical divisions more strongly than accounted for by visual-feature computational models that are not explicitly optimized to distinguish categories. The categorical clusters appear to be consistent across individual human brains. However, the continuous representational space is unique to each individual and predicts individual idiosyncrasies in object similarity judgements. The representation flexibly emphasizes task-relevant category divisions through subtle distortions of the representational geometry. MEG results further suggest that the categorical divisions emerge dynamically, with the latency of categoricality peaks suggesting a role for recurrent processing.

Modern population approaches for discovering neural representations and for discriminating among algorithms that might produce those representations.

Speaker: James J. DiCarlo, MD, PhD; Professor of Neuroscience Head, Department of Brain and Cognitive Sciences Investigator, McGovern Institute for Brain Research Massachusetts Institute of Technology, Cambridge, USA
Authors: Ha Hong and Daniel Yamins Department of Brain and Cognitive Sciences and McGovern Institute for Brain Research Massachusetts Institute of Technology, Cambridge, USA

Visual object recognition (OR) is a central problem in systems neuroscience, human psychophysics, and computer vision. The primate ventral stream, which culminates in inferior temporal cortex (IT), is an instantiation of a powerful OR system. To understand this system, our approach is to first drive a wedge into the problem by finding the specific patterns of neuronal activity (a.k.a. neural “representations”) that quantitatively express the brain’s solution to OR. I will argue that, to claim discovery of a neural “representation” for OR, one must show that a proposed population of visual neurons can perfectly predict psychophysical phenomena pertaining to OR. Using simple decoder tools, we have achieved exactly this result, demonstrating that IT representations (as opposed to V4 representations) indeed predict OR phenomena. Moreover, we can “invert” the decoder approach to use large-scale psychophysical measurements to make new, testable predictions about the IT representation. While decoding methods are powerful for exploring the link between neural activity and behavior, they are less well suited for addressing how pixel representations (i.e. images) are transformed into neural representations that subserve OR. To address this issue, we have adopted the representational dissimilarity matrices (RDM) approach promoted by Niko Kriegeskorte. We have recently discovered novel models (i.e. image-computable visual features) that, using the RDM measure of success, explain IT representations dramatically better than all previous models.

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Organizers: Stephan de la Rosa & Heinrich Bülthoff; Max Planck Institute for Biological Cybernetics
Presenters: Nick Barraclough, Cristina Becchio, Stephan de la Rosa, Ehud Zohary, Martin. A. Giese

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Symposium Description

The visual recognition of actions is critical for humans when interacting with their physical and social environment. The unraveling of the underlying processes has sparked wide interest in several fields including computational modeling, neuroscience, and psychology. Recent research endeavors on how people recognize actions provide important insights into the mechanisms underlying action recognition. Moreover, they give new ideas for man-machine interfaces and have implications for artificial intelligence. The aim of the symposium is to provide an integrative view on recent advances in our understanding of the psychological and neural processes underlying action recognition. Speakers will discuss new and related developments in the recognition of mainly object- and human-directed actions from a behavioral, neuroscientific, and modeling perspective. These developments include, among other things, a shift from the investigation of isolated actions to the examination of action recognition under more naturalistic conditions including contextual factors and the human ability to read social intentions from the recognized actions. These findings are complemented by neuroscientific work examining the action representation in motor cortex. Finally, a novel theory of goal-directed actions will be presented that integrates the results from various action recognition experiments. The symposium will first discuss behavioral and neuroscientific aspects of action recognition and then will shift its attention to the modeling of the processes underlying action recognition. More specifically, Nick Barraclough will present research on action recognition using adaptation paradigms and object-directed and locomotive actions. He will talk about the influence of the observer’s mental state on action recognition using displays that present the action as naturalistic as possible. Cristina Becchio will talk about actions and their ability to convey social intentions. She will present research on the translation of social intentions into kinematic patterns of two interacting persons and discuss the observers’ ability to visually use these kinematic cues for inferring social intentions. Stephan de la Rosa will focus on social actions and talk about the influence of social and temporal context on the recognition of social actions. Moreover, he will present research on the visual representation underlying the recognition of social interactions. Ehud Zohary will discuss the representation of actions within the motor pathway using fMRI and the sensitivity of the motor pathway to visual and motor aspects of an action. Martin Giese will wrap up the symposium by presenting a physiologically plausible neural theory for the perception of goal-directed hand actions and discuss this theory in the light of recent physiological findings. The symposium is targeted towards the general VSS audience and provides an comprehensive and integrative view about an essential ability of human visual functioning.

Presentations

Other peoples’ actions interact within our visual system

Speaker: Nick Barraclough; Department of Psychology, University of York, York, UK

Perception of actions relies on the behavior of neurons in the temporal cortex that respond selectively to the actions of other individuals. It is becoming increasingly clear that visual adaptation, well known for influencing early visual processing of more simple stimuli, appears also to have an influence at later processing stages where actions are coded. In a series of studies we, and others, have been using visual adaptation techniques to attempt to characterize the mechanisms underlying our ability to recognize and interpret information from actions. Action adaptation generates action aftereffects where perception of subsequent actions is biased; they show many of the characteristics of both low-level and high-level face aftereffects, increasing logarithmically with duration of action observation, and declining logarithmically over time. I will discuss recent studies where we have investigated the implications for action adaptation in naturalistic social environments. We used high-definition, orthostereoscopic presentation of life-sized photorealistic actors on a 5.3 x 2.4 m screen in order to maximize immersion in a Virtual Reality environment. We find that action recognition and judgments we make about the internal mental state of other individuals is changed in a way that can be explained by action adaptation. Our ability to recognize and interpret the actions of an individual is dependent, not only on what that individual is doing, but the effect that other individuals in the environment have on our current brain state. Whether or not two individuals are actually interacting in the environment, it seems they interact within our visual system.

On seeing intentions in others’ movements

Speaker: Cristina Becchio; Centre for Cognitive Science, Department of Psychology, University of Torino, Torino, Italy; Department of Robotics, Brain, and Cognitive Science, Italian Institute of Technology, Genova, Italy

Starting from Descartes, philosophers, psychologists, and more recently neuroscientists, have often emphasized the idea that intentions are not things that can be seen. They are mental states and perception cannot be smart enough to reach the mental states that are hidden away (imperceptible) in the other person’s mind. Based on this assumption, standard theories of social cognition have mainly focused the contribution of higher-level cognition to intention understanding. Only recently, it has been recognized that intentions are deeply rooted in the actions of interacting agents. In this talk, I present findings from a new line of research showing that intentions translate into differential kinematic patterns. Observers are especially attuned to kinematic information and can use early differences in visual kinematics to anticipate what another person will do next. This ability is crucial not only for interpreting the actions of individual agents, but also to predict how, in the context of a social interaction between two agents, the actions of one agent relate to the actions of a second agent.

The influence of context on the visual recognition of social actions.

Speaker: Stephan de la Rosa; Department Human Perception, Cognition and Action; Max Planck Institute for Biological Cybernetics, Tübingen, Germany
Authors: Stephan Streuber, Department Human Perception, Cognition and Action; Max Planck Institute for Biological Cybernetics, Tübingen, Germany Heinrich Bülthoff, Department Human Perception, Cognition and Action; Max Planck Institute for Biological Cybernetics, Tübingen, Germany

Actions do not occur out of the blue. Rather, they are often a part of human interactions and are, therefore, embedded in an action sequence. Previous research on visual action recognition has primarily focused on elucidating the perceptual and cognitive mechanisms in the recognition of individual actions. Surprisingly, the social and temporal context, in which actions are embedded, has received little attention. I will present studies examining the importance of context on action recognition. Specifically, we examined the influence of social context (i.e. competitive vs. cooperative interaction settings) on the observation of actions during real life interactions and found that social context modulates action observation. Moreover, we investigated the perceptual and temporal factors (i.e. action context as provided by visual information about preceding actions) on action recognition using an adaptation paradigm. Our results provide evidence that experimental effects are modulated by temporal context. These results in the way that action recognition is not guided by the immediate visual information but also by temporal and social contexts.

On the representation of viewed action in the human motor pathways

Speaker: Ehud Zohary; Department of Neurobiology, Alexander Silberman Institute of Life Sciences, Hebrew University of Jerusalem, Israel

I will present our research on the functional properties of brain structures which are involved in object-directed actions. Specifically, we explore the nature of viewed-action representation using functional magnetic resonance imaging (fMRI). One cortical region involved in action recognition is anterior intraparietal (AIP) cortex. The principal factor determining the response in AIP is the identity of the observed hand. Similar to classical motor areas, AIP displays clear preference for the contralateral hand, during motor action (i.e., object manipulation) without visual feedback. This dual visuomotor grasping representation suggests that AIP may be involved in the specific motor simulation of hand actions. Furthermore, viewing object-directed actions (from an egocentric-viewpoint, as in self action) elicits a similar selectivity for the contralateral hand. However, if the viewed action is seen from an allocentric viewpoint (i.e. being performed by another person facing the viewer), greater activation in AIP is found for the ipsilateral hand. Such a mapping may be useful for imitation of hand action (e.g. finger tapping) made by someone facing us which is more accurate when using the opposite (mirror-image) hand. Finally, using the standard “center-out” task requiring visually guided hand movements in various directions, we show that primary motor cortex (M1) is sensitive to both motor and visual components of the task. Interestingly, the visual aspects of movement are encoded in M1 only when they are coupled with motor consequences. Together, these studies indicate that both perceptual and motor aspects are encoded in the patterns of activity in the cortical motor pathways.

Neural theory for the visual perception of goal-directed actions and perceptual causality

Speaker: Martin. A. Giese; Section for Computational Sensomotorics, Dept. for Cognitive Neurology, HIH and CIN, University Clinic Tübingen, Germany
Authors: Falk Fleischer (1,2); Vittorio Caggiano (2,3); Jörn Pomper (2), Peter Thier (2) 1) Section for Computational Sensomotorics 2) Dept. for Cognitive Neurology, HIH and CIN, University Clinic Tübingen, Germany 3) McGovern Institute for Brain Research, M.I.T., Cambridge, MA Supported by the DFG, BMBF, and EU FP7 projects AMARSI, ABC, and the Human Brain Project.

The visual recognition of goal-directed movements even from impoverished stimuli, is a central visual function with high importance for survival and motor learning. In cognitive neuroscience and brain imaging a number of speculative theories have been proposed that suggest possible computational processes that might underlie this function. However, these theories typically leave it completely open how the proposed functions might be implemented by local cortical circuits. Complementing these approaches, we present a physiologically-inspired neural theory for the visual processing of goal-directed actions, which provides a unifying account for existing neurophysiological results on the visual recognition of hand actions in monkey cortex. The theory motivated, and partly correctly predicted specific computational properties of action-selective neurons in monkey cortex, which later could be verified physiologically. Opposed to several dominant theories in the field, the model demonstrates that robust view-invariant action recognition from monocular videos can be accomplished without a reconstruction of the three-dimensional structure of the effector, or a critical importance of an internal simulation of motor programs. As a ‘side-effect’, the model also reproduces simple forms of causality perception, predicting that these stimuli might be processed by similar neural structures as natural hand actions. Consistent with this prediction, F5 mirror neurons can be shown to respond selectively to such stimuli. This suggests that the processing of goal-directed actions might be accounted for by relatively simple neural mechanisms that are accessible by electrophysiological experimentation.

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Organizers: Franco Pestilli & Ariel Rokem; Stanford University
Presenters: Ariel Rokem, Andrew Bock, Holly Bridge, Suzy Scherf, Hiromasa Takemura, David Van Essen

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Symposium Description

For about two decades, functional MR imaging has allowed investigators to map visual cortex in the living human brain. Vision scientists have identified clusters of cortical regions with different functional properties. The function of these maps is determined by both the selectivity of their neurons, as well as their connections. Communication between cortical regions is carried by long-range white-matter fascicles. The wiring of these fascicles is important for implementing the perceptual functions of the visual maps in the occipital, temporal and parietal cortex. Magnetic resonance diffusion imaging (dMRI) and computational tractography are the only technologies that enable scientists to measure the white matter in the living human brain. In the decade since their development, these technologies revolutionized our understanding of the importance of human white-matter for health and disease. Recent advances in dMRI and fiber tractography have opened new avenues of understanding the white-matter connections in the living human brain. With the advent of these technologies we are for the first time in a position to draw a complete wiring diagram of the human visual system. By probing the motion of water molecules at the micron scale, dMRI can be used to study the microstructural properties and geometric organization of the visual white-matter fascicles. These measurements in living brains can help clarify the relationship between the properties of the tissue within the fascicles and visual perception, both in healthy individuals and in cases where vision is impeded through disease. Prior to these measurements, the white matter was thought of as a passive cabling system. But modern measurements show that white matter axons and glia respond to experience and that the tissue properties of the white matter are transformed during development and following training. The white matter pathways comprise a set of active wires and the responses and properties of these wires predict human cognitive and perceptual abilities. This symposium targets a wide range of investigators working in vision science by providing an introduction to the principles of dMRI measurements, algorithms used to identify anatomical connections and models used to characterize white-matter properties. The speakers have pioneered the use of diffusion and functional MRI and fiber tractography to study the human visual white-matter in answering a wide range of scientific questions: connectivity, development, plasticity. The symposium will also introduce publicly available resources (analysis software and data) to help advance the study of the human visual cortex and white-matter, with special emphasis on the high-quality MR measurements provided by the Human Connectome Project (HCP).

Presentations

Measuring and modelling of diffusion and white-matter tracts

Speaker: Ariel Rokem; Stanford University
Authors: Franco Pestilli

This talk will present a general methodological overview of diffusion MRI (dMRI), with a special focus on methods used to image connectivity and tissue properties in the human visual system. We will start by describing the principles of dMRI measurements. We will then provide an overview of models that are used to describe the signal and make inferences about the properties of the tissue and the trajectories of fiber fascicles in white-matter. We will focus on the classical Diffusion Tensor Model (DTM), which is used in many applications, and on the more recent development of Sparse Fascicle Models (SFM), which are more realistic representations of the signal as a combination of signals from different fascicles. Using cross-validation, we have found that DTM provides an accurate representation of the data, better than the reliability of a repeated measurement. SFM provide even more accurate models of the data, and particularly in regions where different fiber tracts cross. In the second part of the talk, we will focus on tractography. With special emphasis on probabilistic and deterministic tractography. We will introduce ideas about validation of white-matter trajectories and to perform statistical inferences about connectivity between different parts of the visual system. A major problem of the field is that different algorithms provide different estimates of connectivity. This problem is solved by choosing the fiber estimates that best account for the data in a repeated measurement (cross-validation).

Gross topographic organization in the corpus callosum is preserved despite abnormal visual input.

Speaker: Andrew Bock; University of Washington
Authors: Melissa Saenz, University of Laussane; Holly Bridge, Oxford; Ione Fine, University of Washington.

The loss of sensory input early in development has been shown to induce dramatic anatomical and functional changes within the central nervous system. Using probabilistic diffusion tractography, we examined the retinotopic organization of splenial callosal connections within early blind, anophthalmic, achiasmatic and control subjects. Early blind subjects experience prenatal retinal “waves” of spontaneous activity similar to those of sighted subjects, and only lack postnatal visual experience. In anophthalmia, the eye is either absent or arrested at an early prenatal stage, depriving these subjects of both pre- and postnatal visual input, while in achiasma there is a lack of crossing at the optic chiasm such that the white matter projection from each eye is ipsilateral. Comparing these groups provides a way of separating the influence of pre- and postnatal retinal deprivation and abnormal visual input on the organization of visual connections across hemispheres. We found that retinotopic mapping within the splenium was not measurably disrupted in any of these groups compared to visually normal controls. These results suggest that neither prenatal retinal activity nor postnatal visual experience plays a role in the large-scale topographic organization of visual callosal connections within the splenium, and the general method we describe provides a useful way of quantifying the organization of large white matter tracts.

Using diffusion-weighted tractography to investigate dysfunction of the visual system

Speaker: Holly Bridge; Oxford
Authors: Rebecca Millington; James Little; Kate Watkins

The functional consequences of damage to, or dysfunction of, different parts of the visual pathway have been well characterized for many years. Possibly the most extreme dysfunction is the lack of eyes (anophthalmia) which prevents any stimulation of this pathway by light input. In this case, functional MRI indicates the use of the occipital cortex for processing of language, and other auditory stimuli. This raises the question of how this information gets to the occipital cortex; are there differences in the underlying anatomical connectivity or can existing pathways be used to carry different information? Here I’ll describe several approaches we have taken to try to understand the white matter connectivity in anophthalmia using diffusion tractography. Damage to the visual pathway can also be sustained later in life, either to the periphery or to the post-chiasmatic pathway (optic tract, lateral geniculate nucleus, optic radiation or visual cortex). When damage occurs in adulthood, any changes to white matter are likely to be the result of degeneration. Sensitive measures of white matter integrity can be used to illustrate patterns of degeneration in patient populations. However, it is also the case that in the presence of lesions, and where white matter tracts are relatively small (e.g. optic tract) measures derived from diffusion-weighted imaging can be misleading. In summary I will present an overview of the potential for employing diffusion tractography to understand plasticity and degeneration in the abnormal visual system, highlighting potential confounds that may arise in patient populations.

Structural properties of white matter circuits necessary for face perception

Speaker: Suzy Scherf; Penn State
Authors: Marlene Behrmann, Carnegie Mellon University; Cibu Thomas, NIH; Galia Avidan, Beer Sheva University; Dan Elbich, Penn State University

White matter tracts, which communicate signals between cortical regions, reportedly play a critical role in the implementation of perceptual functions. We examine this claim by evaluating structural connectivity, and its relationship to neural function, in the domain of face recognition in both developing individuals and those with face recognition deficits. In all studies, we derived the micro- as well as macro-structural properties of the inferior longitudinal fasciculus (ILF) and of the inferior fronto-occipital fasciculus (IFOF), which connect distal regions of cortex that respond preferentially to faces. In participants aged 6-23 years old, we observed age-related differences in both the macro- and micro-structural properties of the ILF. Critically, these differences were specifically related to an age-related increase in the size of the functionally defined fusiform face area. We then demonstrated the causal nature of the structure-function relationship in individuals who are congenitally prosopagnosic (CP) and in an aging population (who exhibits an age-related decrement in face recognition). The CPs exhibited reduced volume of the IFOF and ILF, which was related to the severity of their face processing deficit. Similarly, in the older population there were also significant reductions in the structural properties of the ILF and IFOF that were related to their behavioral performance. Finally, we are exploring whether individual differences in face-processing behavior of normal adults are related to variations in these structure-function relations. This dynamic association between emerging structural connectivity, functional architecture and perceptual behavior reveals the critical role of neural circuits in human cortex and perception.

A major white-matter wiring between the ventral and dorsal stream

Speaker: Hiromasa Takemura; Stanford University
Authors: Brian Wandell

Over the last several decades, visual neuroscientists have learned how to use fMRI to identify multiple visual field maps in the living human brain. Several theories have been proposed to characterize the organization of these visual field maps, and a key theory with substantial support distinguishes dorsal stream involving with spatial processing and ventral stream involving categorical processing. We combined fMRI, diffusion MRI and fiber tractography to identify a major white matter pathway, the Vertical Occipital Fasciculus (VOF), connecting maps within the dorsal and ventral visual streams. We use a model-based method, LInear Fascicle Evaluation (LIFE), to assess the statistical evidence supporting the VOF wiring pattern. There is strong evidence supporting the hypothesis that dorsal and ventral streams of visual maps communicate through the VOF. This pathway is large and its organization suggests that the human ventral and dorsal visual maps communicate substantial information through V3A/B and hV4/VO-1. We suggest that the VOF is crucial for transmitting signals between regions that encode object properties including form, identity and color information and regions that map spatial location to action plans. Findings on the VOF will extend the current understandings of the human visual field map hierarchy.

What is the Human Connectome Project telling us about human visual cortex?

Speaker: David Van Essen; Washington University

The Human Connectome Project (HCP) is acquiring and sharing vast amounts of neuroimaging data from healthy young adults, using high-resolution structural MRI, diffusion MRI, resting-state fMRI, and task-fMRI. Together, these complementary modalities provide invaluable information and insights regarding the organization and connectivity of human visual cortex. This presentation will highlight recent results obtained using surface-based analysis and visualization approaches to characterize structural and functional connectivity of visual cortex in individuals and group averages.

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Organizer: Jonathan Peirce; University of Nottingham
Presenters: Jonathan Peirce, Anitha Pasupathy, Zoe Kourtzi, Gunter Loffler, Tim Andrews, Hugh Wilson

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Symposium Description

A great deal is known about the early stages of visual processing, whereby light of different wavelengths is detected and filtered in such a way as to represent something approximating “edges”. A large number of studies are also examining the “high-level” processing and representation of visual objects; the representation of faces and scenes, and the visual areas responsible for their processing. Remarkably few studies examine either the intervening “mid-level” representations or the visual areas that are involved in this level of processing. This symposium will examine what form these intermediate representations might take, and what methods we have available to study such mechanisms. The speakers have used a variety of methods to try and understand mid-level processing and the associated visual areas. Along the way, a number of questions will be considered. Do we even have intermediate representations; surely higher-order object representations could be built directly on the outputs of V1 cells since all of the information is available there? How does such a representation not fall foul of the problem of parameter explosion? What aspects of the visual scene are encoded at this level? How could we understand such representations further? Why have we not made further progress in this direction before; is the problem simply too hard to study? The symposium is designed for attendees of all levels and will involve a series of 20 minute talks (each including 5 minutes for questions) from each of the speakers. We hope to encourage people that this is an important and tangible problem that vision scientists should be working hard to solve.

Presentations

Compound feature detectors in mid-level vision

Speaker: Jonathan Peirce; University of Nottingham

A huge number of studies have considered low-level visual processes (such as the detection of edges, colors and motion) and high-level visual processes (such as the processing of faces and scenes). Relatively few studies examine the nature of intermediate visual representations, or “mid-level” vision. One approach to studying mid-level visual representations might be to try and understand the mechanisms that combine the outputs of V1 neurons to create an intermediate feature detector. We have used adaptation techniques to try and probe the existence of detectors for combinations of sinusoids that might form plaid form detectors or curvature detectors. We have shown for both of these features that adaptation effects to the compound has been greater than predicted by adaptation to the parts alone, and that this is greatest when the components form a plaid that we perceive as coherent or a curve that is continuous. To create such representations requires simple logical AND-gates, which might be formed simply by summing the nonlinear outputs of V1 neurons. Many questions remain however, about where in the visual cortex these representations are stored, and how the different levels of representation interact.

Boundary curvature as a basis of shape encoding in macaque area V4

Speaker: Anitha Pasupathy; University of Washington

The broad goal of research in my laboratory is to understand how visual form is encoded in the intermediate stages of the ventral visual pathway, how these representations arise and how they contribute to object recognition behavior. Our current focus is primate V4, an area known to be critical for form processing. Given the enormity of the shape-encoding problem, our strategy has been to test specific hypotheses with custom-designed, parametric, artificial stimuli. With guidance from shape theory, computer-vision and psychophysical literature we identify stimulus features (for example T-junctions) that might be critical in natural vision and work these into our stimulus design so as to progress in a controlled fashion toward more naturalistic stimuli. I will present examples from our past and current experiments that successfully employ this strategy and have led to the discovery of boundary curvature as a basis for shape encoding in area V4. I will conclude with some brief thoughts on how we might move from the highly-controlled stimuli we currently use to the more rich and complex stimuli of natural vision.

Adaptive shape coding in the human visual brain

Speaker: Zoe Kourtzi; University of Birmingham

In the search for neural codes, we typically measure responses to input stimuli alone without considering their context in space (i.e. scene configuration) or time (i.e. temporal history). However, accumulating evidence suggests an adaptive neural code that is dynamically shaped by experience. Here, we present work showing that experience plays a critical role in molding mid-level visual representations and shape perception. Combining behavioral and brain imaging measurements we demonstrate that learning optimizes the binding of local elements into shapes, and the selection of behaviorally relevant features for shape categorization. First, we provide evidence that the brain flexibly exploits image regularities and learns to use discontinuities typically associated with surface boundaries for contour linking and target identification. Specifically, learning of regularities typical in natural contours (i.e., collinearity) can occur simply through frequent exposure, generalize across untrained stimulus features, and shape processing in occipitotemporal regions. In contrast, learning to integrate discontinuities (i.e., elements orthogonal to contour paths) requires task-specific training, is stimulus dependent, and enhances processing in intraparietal regions. Second, by reverse correlating behavioral and fMRI responses with noisy stimulus trials, we identify the critical image parts that determine the observers’ choice in a shape categorization task. We demonstrate that learning optimizes shape templates by tuning the representation of informative image parts in higher ventral cortex. In sum, we propose that similar learning mechanisms may mediate long-term optimization through development, tune the visual system to fundamental principles of feature binding, and shape visual category representations.

Probing intermediate stages of shape processing

Speaker: Gunter Loffler; Glasgow Caledonian University

The visual system provides a representation of what and where objects are. This entails parsing the visual scene into distinct objects. Initially, the visual system encodes information locally. While interactions between adjacent cells can explain how local fragments of an object’s contour are extracted from a scene, more global mechanisms have to be able to integrate information beyond that of neighbouring cells to allow for the representation of extended objects. This talk will examine the nature of intermediate-level computations in the transformation from discrete local sampling to the representation of complex objects. Several paradigms were invoked to study how information concerning the position and orientation of local signals is combined: a shape discrimination task requiring observers to discriminate between contours; a shape coherence task measuring the number of elements required to detect a contour; a shape illusion in which positional and orientational information is combined inappropriately. Results support the notion of mechanisms that integrate information beyond that of neighbouring cells and are optimally tuned to a range of different contour shapes. Global integration is not restricted to central vision: peripheral data show that certain aspects of this process only emerge at intermediate stages. Moreover, intermediate processing appears vulnerable to damage. Diverse clinical populations (migraineurs, pre-term children and children with Cortical Visual Impairment) show specific deficits for these tasks that cannot be accounted for by low-level processes. Taken together, evidence is converging towards the identification of an intermediate level of processing, at which sensitivity to global shape attributes emerges.

Low-level image properties of visual objects explain category-selective patterns of neural response across the ventral visual pathway

Speaker: Tim Andrews; University of York

Neuroimaging research over the past 20 years has begun to reveal a picture of how the human visual system is organized. A key organizing principle that has arisen from these studies is the distinction between low-level and high-level visual regions. Low-level regions are organized into visual field maps that are tightly linked to the image properties of the stimulus. In contrast, high-level visual areas are thought to be arranged in modules that are selective for particular object categories. It is unknown, however, whether this selectivity is truly based on object category, or whether it reflects tuning for low-level features that are common to images from a particular category. To address this issue, we compared the pattern of neural response elicited by each object category with the corresponding low-level properties of images from each object category. We found a strong positive correlation between the neural patterns and the underlying low-level image properties. Importantly, the correlation was still evident when the within-category correlations were removed from the analysis. Next, we asked whether low-level image properties could also explain variation in the pattern of response to exemplars from individual object categories (faces or scenes). Again, a positive correlation was evident between the similarity in the pattern of neural response and the low-level image properties of exemplars from individual object categories. These results suggest that the pattern of response in high-level visual areas may be better explained by the image statistics of visual stimuli than by their associated categorical or semantic properties.

From Orientations to Objects: Configural Processing in the Ventral Stream

Speaker: Hugh Wilson; York University

I shall review psychophysical and fMRI evidence for a hierarchy of intermediate processing stages in the ventral or form vision system. A review of receptive field sizes from V1 up to TE indicates an increase in diameter by a factor of about 3.0 from area to area. This is consistent with configural combination of adjacent orientations to form curves or angles, followed by combination of curves and angles to form descriptors of object shapes. Psychophysical and fMRI evidence support this hypothesis, and neural models provide a plausible explanation of this hierarchical configural processing.

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Organizers: Jessica Collins & Ingrid Olson; Temple University
Presenters: Winrich Friewald, Stefano Anzellotti, Jessica Collins, Galia Avidan, Ed O’Neil

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Symposium Description

Extensive research supports the existence of a specialized face-processing network that is distinct from the visual processing areas used for general object recognition. The majority of this work has been aimed at characterizing the response properties of the fusiform face area (FFA) and the occipital face area (OFA), which are thought to constitute the core network of brain regions responsible for facial identification. Recent findings of face-selective cortical regions in more anterior regions of the macaque brain– in the ventral anterior temporal lobe (vATL) and in the orbitofrontal cortex casts doubt on this simple characterization of the face network. This macaque research is supported by fMRI research in humans showing functionally homologous face-processing areas in the vATLs of humans. In addition, there is intracranial EEG and neuropsychology research all pointing towards the critical role of the vATL in some aspect of face processing. The function of the vATL face patches is relatively unexplored and the goal of this symposium is to bring together researchers from a variety of disciplines to address the following question: What is the functional role of the vATLs in face perception and memory and how does it interact with the greater face network? Speakers will present recent findings organized around the following topics: 1) The response properties of the vATL face areas in humans; 2) the response properties of the vATL face area in non-human primates; 3) The connectivity of vATL face areas with the rest of the face-processing network; 4) The role of the vATLs in the face-specific visual processing deficits in prosopagnosia; 5) The sensitivity of the vATLs to conceptual information; and 6) the representational demands that modulate the involvement of the perirhinal cortex in facial recognition. The implications of these findings to theories of face processing and object processing more generally will be discussed.

Presentations

Face-processing hierarchies in primates

Speaker: Winrich Friewald; The Rockefeller University

The neural mechanisms of face recognition have been extensively studied in both humans and macaque monkeys. Results obtained with similar technologies, chiefly functional brain imaging now allows for detailed cross-species comparisons of face-processing circuitry. A crucial node in this circuit, located at the interface of face perception and individual recognition, is located in the ventral anterior temporal lobe. In macaque monkeys, face selective cells have been found in this region through electrophysiological recordings, a face-selective patch identified with functional magnetic resonance imaging (fMRI), and the unique functional properties of cells within these fMRI-identified regions characterized, suggesting a role in invariant face identification. Furthermore activity in this patch been causally linked, through combinations of electrical microstimulation and psychophysics, to different kinds of face recognition behavior. Not far away from this face selective region, experience-dependent specializations for complex object shapes and their associations have been located, and the mechanisms of these processes studied extensively. In my talk I will present this work on face processing in the ventral anterior temporal lobe of the macaque brain, its relationship to face processing in other face regions and to processes in neighboring regions, its implications for object recognition in general, and the impact of this work for understanding the mechanisms of human face recognition.

Invariant representations of face identity in the ATL

Speaker: Stefano Anzellotti; Harvard University
Authors: Alfonso Caramazza, Harvard University

A large body of evidence has documented the involvement of occipitotemporal regions in face recognition. Neuropsychological studies found that damage to the anterior temporal lobes (ATL) can lead to face recognition deficits, and recent neuroimaging research has shown that the ATL contain regions that respond more strongly to faces than to other categories of objects. What are the different contributions of anterior temporal and occipitotemporal regions to face recognition? In a series of fMRI studies, we investigated representations of individual faces in the human ATL using computer generated face stimuli for which participants did not have individual-specific associated knowledge. Recognition of face identity from different viewpoints and from images of part of the face was tested, using an approach in which pattern classifiers are trained and tested on the responses to different stimuli depicting the same identities. The anterior temporal lobes were found to encode identity information about faces generalizing across changes in the stimuli. Invariant information about face identity was found to be lateralized to the right hemisphere. Some tolerance across image transformations was also detected in occipitotemporal regions, but it was limited to changes in viewpoint, suggesting a process of increasing generalization from posterior to anterior temporal areas. Consistent with this interpretation, information about identity-irrelevant details of the images was found to decline moving along the posterior-anterior axis, and was not detected in the ATL.

The role of the human vATL face patches in familiar face processing

Speaker: Jessica Collins; Temple University
Authors: Ingrid Olson, Temple University

Studies of nonhuman primates have reported the existence of face sensitive patches in the ventral anterior temporal lobes. Using optimized imaging parameters recent fMRI studies have identified a functionally homologous brain region in the ventral anterior temporal lobes (vATLs) of humans. The human vATL shows sensitivity to both perceptual and conceptual features of faces, suggesting that it is involved in some aspects of both face perception and face memory. Supporting a role of the vATLs in face perception, activity patterns in the human vATL face patches discriminate between unfamiliar facial identities, and unilateral damage to the vATLs impairs the ability to make fine-grained discriminations between simultaneously displayed faces when morphed stimuli are used. Supporting a role of the vATLs in face memory, activity in the vATLs is up-regulated for famous faces and for novel faces paired with semantic content. The left ATL appears to be relatively more sensitive to the verbal or semantic aspects of faces, while the right ATL appears to be relatively more sensitive to visual aspects of face, consistent with lateralized processing of language. We will discuss the implications of these findings and propose a revised model of face processing in which the vATLs serve a centralized role in linking face identity to face memory as part of the core visual face-processing network.

Structural and functional impairment of the face processing network in congenital prosopagnosia

Speaker: Galia Avidan; Ben Gurion University
Authors: Michal Tanzer, Ben Gurion University; Marlene Behrmann, Carnegie Mellon University

There is growing consensus that accurate and efficient face recognition is mediated by a neural circuit comprised of a posterior “core” and an anterior “extended” set of regions. In a series of functional and structural imaging studies, we characterize the distributed face network in individuals with congenital prosopagnosia (CP) – a lifelong impairment in face processing – relative to that of matched controls. Interestingly, our results uncover largely normal activation patterns in the posterior core face patches in CP. More recently, we also documented normal activity of the amygdala (emotion processing) as well as normal, or even enhanced functional connectivity between the amygdala and the core regions. Critically, in the same individuals, activation of the anterior temporal cortex, which is thought to mediate identity processing, was reduced and connectivity between this region and the posterior core regions was disrupted. The dissociation between the neural profiles of the anterior temporal lobe and amygdala was evident both during a task-related face scan and during a resting state scan, in the absence of visual stimulation. Taken together, these findings elucidate selective disruptions in neural circuitry in CP, and are also consistent with impaired white matter connectivity to anterior temporal cortex and prefrontal cortex documented in these individuals. These results implicate CP as disconnection syndrome, rather than an alteration localized to a particular brain region. Furthermore, they offer an account for the known behavioral differential difficulty in identity versus emotional expression recognition in many individuals with CP.

Functional role and connectivity of perirhinal cortex in face processing

Speaker: Ed O’Neil; University of Western Ontario
Authors: Stefan Köhler, University of Western Ontario

The prevailing view of medial temporal lobe (MTL) functioning holds that its structures are dedicated to declarative long-term memory. Recent evidence challenges this view, suggesting that perirhinal cortex (PrC), which interfaces the MTL with the ventral visual pathway, supports highly integrated object representations that are critical for perceptual as well as for memory-based discriminations. Here, we review research conducted with fMRI in healthy individuals that addresses the role of PrC, and its functional connectivity, in the context of face processing. Our research shows that (i) PrC exhibits a performance-related involvement in recognition-memory as well as in perceptual oddball judgments for faces; (ii) PrC involvement in perceptual tasks is related to demands for face individuation; (ii) PrC exhibits resting-state connectivity with the FFA and the amygdala that has behavioural relevance for the face-inversion effect; (iii) task demands that distinguish recognition-memory from perceptual-discrimination tasks are reflected in distinct patterns of functional connectivity between PrC and other cortical regions, rather than in differential PrC activity. Together, our findings challenge the view that mnemonic demands are the sole determinant of PrC involvement in face processing, and that its response to such demands uniquely distinguishes its role from that of more posterior ventral visual pathway regions. Instead, our findings point to the importance of considering the nature of representations and functional connectivity in efforts to elucidate the contributions of PrC and other cortical structures to face processing.

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Organizers: Brian J. White & Douglas P. Munoz; Centre for Neuroscience Studies, Queen’s University, Kingston, ON, Canada
Presenters: Jared Abrams, Wolfgang Einhäuser, Brian J. White, Michael Dorr, Neil Mennie

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Symposium Description

Understanding how we perceive and act upon complex natural environments is one of the most pressing challenges in visual neuroscience, with applications that have potential to revolutionize our understanding of the brain, machine vision, and artificial intelligence, to clinical applications such as the detection of visual or mental disorders and neuro-rehabilitation. Until recently, the study of active vision – how visual stimuli give rise to eye movements, and conversely how eye movements influence vision – has largely been restricted to simple stimuli in artificial laboratory settings. Historically, much work on the visual system has been accomplished in this way, but to fully understand vision it is essential to measure behavior under the conditions in which visual systems naturally evolved. This symposium covers some of the latest research on vision and eye movements in natural environments. The talks will explore methods of quantifying natural vision, and compare/contrast behavior across various levels of stimulus complexity and task constraint, from visual search in natural scenes (Abrams, Bradley & Geisler), to unconstrained viewing of natural dynamic video in humans (Dorr, Wallis & Bex), and non-human primates during single-cell recording (White, Itti & Munoz), and real-world gaze behavior using portable eye-tracking (Einhäuser & ‘t Hart; Mennie, Zulkifli, Mahadzir, Miflah & Babcock). Thus, the symposium should be of interest to a wide audience from visual psychophysicists, to oculomotor neurophysiologists, and cognitive/computational scientists.

Presentations

Fixation search in natural scenes: a new role for contrast normalization

Speaker: Jared Abrams; Center for Perceptual Systems, University of Texas, Austin, USA
Authors: Chris Bradley, Center for Perceptual Systems, University of Texas, Austin; Wilson S. Geisler, Center for Perceptual Systems, University of Texas, Austin.

Visual search is a fundamental behavior, yet little is known about search in natural scenes. Previously, we introduced the ELM (entropy limit minimization) fixation selection rule, which selects fixations that maximally reduce uncertainty about the location of the target. This rule closely approximates the Bayesian optimal decision rule, but is simpler computationally, making the ELM rule a useful benchmark for characterizing human performance. Previously, we found that the ELM rule predicts several aspects of fixation selection in naturalistic (1/f) noise, including the distributions of fixation location, saccade magnitude, and saccade direction. However, the ELM rule is only optimal when the detectability of the target (the visibility map) falls off from the point of fixation in the same way for all potential fixation locations, which holds for backgrounds with relatively constant spatial structure, like statistically stationary 1/f noise. Most natural scenes do not satisfy this assumption; they are highly non-stationary. By combining empirical measurements of target detectability in natural backgrounds with a straight-forward mathematical analysis, we arrive at a generalized ELM rule (nELM rule) that is optimal for non-stationary backgrounds. The nELM searcher divides (normalizes) the current target probability map (posterior-probability map) by the estimated local contrast at each location in the map. It then blurs (convolves) this normalized map with the visibility map for a uniform background. The peak of the blurred map is the optimal location for the next fixation. We will describe the predictions and performance of the nELM searcher.

Eye movements in natural scenes and gaze in the real world.

Speaker: Wolfgang Einhäuser; Philipps-University Marburg, Department of Neurophysics, Marburg, Germany
Authors: Bernard Marius ‘t Hart, Philipps-University Marburg, Department of Neurophysics, Marburg, Germany.

Gaze is widely considered a good proxy for spatial attention. We address whether such “overt attention” is related to other attention measures in natural scenes, and to what extent laboratory results on eye movements transfer to real-world gaze orienting. We find that the probability of a target to be detected in a rapid-serial-visual-presentation task correlates with its probability to be fixated during prolonged viewing, and that both measures are similarly affected by modifications to the target’s contrast. This shows a direct link between covert attention in time and overt attention in space for natural stimuli. Especially in the context of computational vision, the probability of an item to be fixated (“salience”) is frequently equated with its “importance”, the probability of it being recalled during scene description. While we confirm a relation between salience and importance, we dissociate these measures by changing an item’s contrast: whereas salience is affected by the actual features, importance is driven by the observer’s expectations about these features based on scene statistics. Using a mobile eye-tracking device we demonstrate that eye-tracking experiments in typical laboratory conditions have limited predictive power for real-world gaze orienting. Laboratory data fail to measure the substantial effects of implicit tasks that are imposed on the participant by the environment to avoid severe costs (e.g., tripping over) and typically fail to include the distinct contributions of eye, head and body for orienting gaze. Finally, we provide some examples for applications of mobile gaze-tracking for ergonomic workplace design and aiding medical diagnostics.

Visual coding in the superior colliculus during unconstrained viewing of natural dynamic video

Speaker: Brian J. White; Centre for Neuroscience Studies, Queen’s University, Kingston, ON, Canada
Authors: Laurent Itti, Dept of Computer Science, University of Southern California, USA; Douglas P. Munoz, Centre for Neuroscience Studies, Queen’s University, Kingston, ON, Canada

The superior colliculus (SC) is a multilayered midbrain structure with visual representations in the superficial-layers (SCs), and sensorimotor representations linked to the control of eye movements/attention in the intermediate-layers (SCi). Although we have extensive knowledge of the SC using simple stimuli, we know little about how the SC behaves during active-vision of complex natural stimuli. We recorded single-units in the monkey SC during unconstrained viewing of natural dynamic video. We used a computational model to predict visual saliency at any retinal location, any point in time. We parsed fixations into tertiles according to the averaged model-predicted saliency value (low, medium, high) in the response field (RF) around the time of fixation (50-400ms post-fixation). The results showed a systematic increase in post-fixation discharge with increasing saliency. We then examined a subset of the total fixations based on the direction of the next saccade (into vs. opposite the RF), under the assumption that saccade direction coarsely indicates the top-down goal of the animal (“value” of the goal-directed stimulus). SCs neurons showed the same enhanced response for greater saliency irrespective of next saccade direction, whereas SCi neurons only showed an enhanced response for greater saliency when the stimulus that evoked it was the goal of the next saccade (was of interest/value). This implies that saliency is controlled closer to the output of the saccade circuit, where priority (combined representation of saliency and relevancy) is presumably signaled and the saccade command is generated. The results support functionally distinct roles of SCs and SCi, whereby the former fit the role of a visual saliency map, and the latter a priority map.

Visual sensitivity under naturalistic viewing conditions

Speaker: Michael Dorr; Schepens Eye Research Institute, Dept of Ophthalmology, Harvard Medical School, and Institute for Neuro- and Bioinformatics, University of Lübeck, Germany
Authors: Thomas S Wallis, Schepens Eye Research Institute, Dept of Ophthalmology, Harvard Medical School, and Centre for Integrative Neuroscience and Department of Computer Science, The University of Tübingen, Tübingen, Germany; Peter J Bex, Schepens Eye Research Institute, Dept of Ophthalmology, Harvard Medical School.

Psychophysical experiments typically use very simple stimuli, such as isolated dots and gratings on uniform backgrounds, and allow no or only very stereotyped eye movements. While these viewing conditions are highly controllable, they are not representative of real-world vision, which is characterized by a complex, broadband input and several eye movements per second. We performed a series of experiments in which subjects freely watched high-resolution nature documentaries and TV shows on a gaze-contingent display. Eye-tracking at 1000 Hz and fast video processing routines allowed us to precisely modulate the stimulus in real time and in retinal coordinates. The task then was to locate either bandpass contrast changes or geometric distortions that briefly appeared in one of four locations relative to the fovea every few seconds. We confirm a well-known loss of sensitivity when video modulations took place around the time of eye movements, i.e. around episodes of high-speed retinal motion. However, we found that replicating the same retinal input in a passive condition, where subjects maintained central fixation and the video was shifted on the screen, led to a comparable loss in sensitivity. We conclude that no process of active, extra-retinal suppression is needed to explain peri-saccadic visual sensitivity under naturalistic conditions. We further find that the detection of spatial modifications depends on the spatio-temporal structure of the underlying scene, such that distortions are harder to detect in areas that vary rapidly across space or time. These results highlight the importance of naturalistic assessment for understanding visual processing.

Spatio-Temporal Dynamics of the use of gaze in natural tasks by a Sumatran Orangutan (Pongo abelli)

Speaker: Neil Mennie; University of Nottingham, Malaysia Campus, Malaysia
Authors: Nadia Amirah Zulkifli, University of Nottingham Malaysia Campus; Mazrul Mahadzir, University of Nottingham Malaysia Campus; Ahamed Miflah, University of Nottingham Malaysia Campus; Jason Babcock, Positive Science LLC, New York, USA.

Studies have shown that in natural tasks where actions are often programmed sequentially, human vision is an active, task-specific process (Land, et al., 1999; Hayhoe et al., 2003). Vision plays an important role in the supervision of these actions, and knowledge of our surroundings and spatial relationships within the immediate environment is vital for successful task scheduling and coordination of complex action. However, little is known about the use of gaze in natural tasks by great apes. Orangutans usually live high in the canopy of the rainforests of Borneo and Sumatra, where a good spatial knowledge of their immediate surroundings must be important to an animal that has the capability to accurately reach/grasp with four limbs and to move along branches. We trained a 9yr old captive born Sumatran orangutan to wear a portable eye tracker and recorded her use of gaze in a number of different tasks such as locomotion, visual search and tool use in an enclosure at the National Zoo of Malaysia. We found that her gaze was task specific, with different eye movement metrics in different tasks. Secondly we also found that this animal made anticipatory, look-ahead eye movements to future targets (Mennie et al., 2007) when picking up sultanas from a board using her upper limbs. This semi-social animal is likely to be capable of the similar, high-level use of gaze to that of a social species of hominidae – humans.

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Vision and eye movements in natural environments

Organizers: Brian J. White & Douglas P. Munoz, Centre for Neuroscience Studies, Queen’s University, Kingston, ON, Canada

Historically, the study of vision has largely been restricted to the use of simple stimuli in controlled tasks where observers are required to maintain stable gaze, or make stereotyped eye movements. This symposium presents some of the latest research aimed at understanding how the visual system behaves during unconstrained viewing of natural scenes, dynamic video, and real-world environments. Understanding how we perceive and act upon complex natural environments has potential to revolutionize our understanding of the brain, from machine vision and artificial intelligence to clinical applications such as the detection of visual or mental disorders and neuro-rehabilitation. More…

Beyond the FFA: The role of the ventral anterior temporal lobes in face processing

Organizer: Jessica Collins & Ingrid Olson, Temple University

Although accruing evidence has shown that face-selective patches in the ventral anterior temporal lobes (vATLs) are highly interconnected with the FFA and OFA, and that they play a necessary role in facial perception and identification, the contribution of these brain areas to the face-processing network remains elusive. The goal of this symposium is to bring together researchers from a variety of disciplines to address the following question: What is the functional role of the vATLs in face perception and memory, and how do they interact with the greater face network? More…

Mid-level representations in visual processing

Organizer: Jonathan Peirce, University of Nottingham

The majority of studies in vision science focus on the representation of low-level features, such as edges, color or motion processing, or on the representation of high-level constructs such as objects, faces and places. Surprisingly little work aims to understand the link between the two; the intermediate representations of “mid-level” vision. This symposium invites a series of speakers that have spent time working on mid-level vision to present their views on what those intermediate representations might be, of the problems that such processing must overcome, and the methods that we might use to understand them better. More…

The visual white-matter matters! Innovation, data, methods and applications of diffusion MRI and fiber tractography

Organizers: Franco Pestilli & Ariel Rokem, Stanford University

Many regions of the cerebral cortex are involved in visual perception and cognition. In this symposium, we will focus on the neuroanatomical connections between them. To study the visual white-matter connections, speakers in this symposium use diffusion MRI (dMRI), an imaging method that probes the directional diffusion of water. The talks will present studies of connectivity between visual processing streams, development of visual white matter, and the role of white matter in visual disorders. We will also survey publicly available resources available to the Vision Sciences community to extend the study of the visual white matter. More…

What are you doing? Recent advances in visual action recognition research.

Organizers: Stephan de la Rosa & Heinrich Bülthoff, Max Planck Institute for Biological Cybernetics

Knowing what another person is doing by visually observing the other person’s actions (action recognition) is critical for human survival. Although humans often have little difficulty recognizing the actions of others, the underlying psychological and neural processes are complex. The understanding of these processes has not only implications for the scientific community but also for the development of man-machine interfaces, robots, and artificial intelligence. The current symposium summarizes recent scientific advances in the realm of action recognition by providing an integrative view on the processes underlying action recognition. More…

Understanding representation in visual cortex: why are there so many approaches and which is best?

Organizers: Thomas Naselaris & Kendrick Kay, Department of Neurosciences, Medical University of South Carolina & Department of Psychology, Washington University in St. Louis

Central to visual neuroscience is the problem of representation: what features of the visual world drive activity in the visual system? In recent years a variety of new methods for characterizing visual representation have been proposed. These include multivariate pattern analysis, representational similarity analysis, the use of abstract semantic spaces, and models of stimulus statistics. In this symposium, invitees will present recent discoveries in visual representation, explaining the generality of their approach and how it might be applicable to future studies. Through this forum we hope to move towards an integrative approach that can be shared across experimental paradigms. More…