Object representations in the parietal cortexSymposium: Friday, May 19, 5:00 – 7:00 pm, Talk Room 1
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Organizers: Erez Freud1, Maryam Vaziri Pashkam2, Yaoda Xu3; 1York University, 2National Institute of Mental Health, 3Yale University
Presenters: Maryam Vaziri-Pashkam, Vladislav Ayzenberg, Anne B. Sereno, Erez Freud, Stefania Bracci, Yaoda Xu
Although the primate ventral visual cortex is well known for its role in visual object processing and representations, a host of recent studies have reported that robust visual object information exists in the primate parietal cortex as well. What kind of object information is present in the parietal cortex, and how does it relate to visual representations formed in the ventral visual cortex? What is its functional significance in perception, tasks and visuomotor planning? How is parietal object representation formed during development? The proposed symposium aims to tackle these critical questions and to inform an updated view of the role of the parietal cortex in object vision and cognition by surveying and incorporating recent evidence. This will be accomplished by bringing together researchers working on this topic from different perspectives and using a diverse set of approaches, including visual psychophysics, brain imaging, human neuropsychology, monkey neurophysiology, and computational modeling. Each speaker will present their findings related to object representations in the parietal cortex and provide answers to the questions raised above. They will also share their thoughts on what they think are the critical and unanswered questions, whether it is possible to form a unified view of the role of the parietal cortex in object processing, and what is needed to push the field forward. There will be a total of six speakers, including four female and two male speakers from North America and Europe at both early and mid-careers. Erez Freud will give a short introduction to the symposium Maryam Vaziri Pashkam will present a data-driven approach to explore object responses in the two pathways. Vlad Ayzenberg will discuss fMRI and computational evidence on the contribution of the parietal cortex to object configural perception. Anne Sereno will discuss physiological and computational findings that suggest that object representations in the parietal cortex are independent of ventral stream representations and are necessary for accurate and optimal performance on object and spatial tasks. Erez Freud will provide a developmental perspective by discussing evidence on the emergence of parietal visual representations under typical and atypical development. Stefania Bracci will discuss the role of behavioral goals in shaping the object space in the two visual pathways. Yaoda Xu will further describe the adaptive nature of parietal object representations by showing how attention, task and working memory may shape these representations.
Two pathways for processing object shapes
Maryam Vaziri-Pashkam1; 1Laboratory of Brain and Cognition, National Institute of Mental Health
The current dominant view on object processing entails that abstract object shape is represented in the ventral visual stream (occipito-temporal cortex). This bias towards the ventral stream has diverted the attention of the field from rigorous study of object responses in the dorsal stream (parietal cortex). To fill the gap in our understanding of object responses in the dorsal stream, we ran a series of experiments using functional MRI to comprehensively study object responses in the human dorsal stream and compared them to those in the ventral stream. We found robust object responses in both streams. Responses in the dorsal parietal cortex, similar to those in the ventral occipitotemporal cortex, were tolerant to changes in position, size, low-level features, and attentional tasks and were sensitive to both static and dynamic cues in the stimuli. In a data-driven approach, we compared the representational structures across the brain. The structure of the visual system, including the visual hierarchy and the dorsal-ventral distinction, emerged from this analysis. Dorsal Stream Regions differed from those in the ventral pathway and early visual cortices. In fact, the structure of the visual hierarchy and the dorsal-ventral stream distinction could be recovered through this bottom-up analysis. The rediscovery of the two-pathway structure using an entirely bottom-up approach demonstrates that first, two pathways exist in the brain for processing object shape information, and second, the dorsal pathway represents features in the visual input distinct from those represented in the ventral pathway.
Dorsal and ventral visual pathways: An expanded neural framework for object recognition
Vladislav Ayzenberg1, Marlene Behrmann1,2; 1Neuroscience Institute and Psychology Department, Carnegie Mellon University, 2Department of Ophthalmology, University of Pittsburgh
Human object recognition is supported by a robust representation of shape that is tolerant to variations in an object's appearance. Such 'global' shape representations are achieved by describing objects via the spatial arrangement of their local features, or structure, rather than by the appearance of the features themselves. Yet, despite its importance for object recognition, the neural mechanisms that support such robust representations of shape remain poorly understood. Here, I will present evidence that the dorsal visual pathway – the primary substrate underlying visuospatial processing and action – plays a crucial role in computing shape information for object recognition. Using fMRI, we find that the dorsal pathway contains regions selective for global shape, which are independent of regions that compute other properties represented by the dorsal pathway (e.g., allocentric relations). Moreover, the multivariate response within dorsal regions is sufficient to both categorize objects at levels comparable to the ventral pathway, as well as mediate representations of shape in the ventral pathway. These results are consistent with an emerging view of object processing, in which complete object representations are formed through the interactions of dorsal and ventral pathways. In this updated view, the ventral pathway is best described as a basis set of local image features, and shape information is, instead, computed by the dorsal pathway. In the final portion of the talk, I will review evidence for this new framework by drawing on neuroimaging data from different levels-of-analysis (single-unit, population-coding level), as well as data from neuropsychology patients.
Independence, not interactions: What simulations suggest about ventral and dorsal pathways.
Anne B. Sereno1,2, Zhixian Han2; 1Psychological Sciences Department, Purdue University, 2Weldon School of Biomedical Engineering, Purdue University
Extensive research suggests visual processing proceeds along two relatively segregated streams into temporal and parietal cortices, important for object and spatial processing, respectively. However, recent evidence suggests that object and spatial processing is present in both visual pathways. The functional significance of the presence of object and spatial properties in both pathways is not yet fully understood. Findings using a population decoding approach in physiology suggest there are fundamental differences between ventral and dorsal processing of both shape and space. Using artificial neural networks, we try to address whether the representations of object in dorsal stream and space in ventral stream play a functional role in spatial and object recognition, respectively. Our simulation results show that a model ventral and a model dorsal pathway, separately trained to do object and spatial recognition, respectively, each actively retained information about both identity and space. In addition, we show that these networks retained different amounts and kinds of identity and spatial information. Finally, we show that this differently retained information about object and space in a two-pathway model (as opposed to single-pathway model) was necessary to accurately and optimally recognize, localize, and, in multiple object displays, successfully bind objects and locations. A computational approach provides a framework to test the functional consequences of two independent visual pathways (with no cross connections) and shows that the findings can provide insight into recent contradictory physiological findings. Critical unanswered questions and implications for current and future understanding of object and spatial processing will be discussed.
Object representations in the dorsal pathway are subject to a protracted and susceptible developmental trajectory.
Erez Freud1; 1Department of Psychology and the Centre for Vision Research, York University
The dorsal visual pathway extends from the occipital lobe to the parietal lobe and generates object representations that promote different visual functions, including visually guided actions, shape recognition and spatial processing. In my talk, I will address two outstanding questions. First, how do dorsal pathway representations emerge throughout development? Second, how does the emergence of these representations modulate perception, action and the dissociation between these functions? To tackle these questions, we conducted a series of behavioral and neuroimaging investigations with typically developed children alongside individuals with neurodevelopmental disorders that affect their early visual experience (i.e., amblyopia) or cortical organization (i.e., cortical resections, ASD). Across the different studies, we find evidence that object representations in the dorsal pathway are not matured even in school-age children. Additionally, we show that visuomotor behaviors, associated with computations carried out by the dorsal pathway, are more susceptible to atypical development than perceptual behaviors. This greater susceptibility was also evident in terms of a reduced functional dissociation between perception and action in children with neurodevelopmental conditions. To conclude, our findings suggest that object representations derived by the dorsal pathway are subject to protracted development. This longer maturation rate might account for the susceptibility of these representations, and their associated behaviors, to neurodevelopmental disorders.
The role of behavioral goals in shaping object representations in the two visual pathways.
Stefania Bracci1, Hans Op de Beeck2; 1Center for Mind/Brain Sciences - CIMeC, University of Trento, Rovereto (TN), Italy, 2KU Leuven, Leuven Brain Institute, Brain & Cognition Research Unit, Leuven, 3000, Belgium.
Classic theories in object vision propose a division between ventral and dorsal stream computations. This standpoint has influenced the way scientists have studied object perception characterizing, in the ventral pathway, representations that support recognition of “what” we see, and in the dorsal pathway, spatial- and action-related representations that support “how” we interact with objects. Recent studies, however, show that this distinction might not fully capture the complexity of ventral and dorsal stream object representations. What if instead to understand this complexity we need to consider object vision in the context of the full repertoire of behavioral goals that underlie human behavior, running far beyond the “what” and “where/how” distinction? In this talk, I will discuss the role of behavioral goals in shaping the organization of object space in the two visual pathways. Complementary, I will show that although object-trained deep neural networks (DNNs) equate humans at object recognition, they struggle at explaining the richness of representational content observed in the visual cortex. I conclude by suggesting that understanding how the brain represents objects needs to not separate object-specific computations from human behavior goals.
Adaptive visual object representation in the human posterior parietal cortex
Yaoda Xu1; 1Psychology Department, Yale University
At any given moment, only a fraction of the visual input may be useful to guide our thoughts and actions. Having the entire visual input available could be distracting and disruptive. To extract the most useful information at each moment, visual processing needs to be selective and adaptive. Here I will show that, compared to visual object representations in the human occipito-temporal cortex (OTC), those in the human posterior parietal cortex (PPC) are more adaptive to serve the task at hand. Specifically, attention and task alter how objects are represented in PPC, with both the differences among the objects and task determining the object representational structure in PPC and with object representations in PPC better tracking the perceived object similarity when objects are task-relevant. Similarly, while the representations of a pair of objects shown together may be predicted by the representations of each constituent object shown in isolation in OTC, this is true in PPC only when the task context is equated. In visual working memory tasks, PPC object representations have been shown to be more resilient to distraction. A recent study shows that while VWM representations of target objects in OTC are entangled with those of distractor objects, those in PPC, however, are more distractor invariant. Such a representational scheme could potentially support PPC’s resilience to distraction in VWM tasks. The adaptive nature of visual object representation in PPC thus allows PPC to play a unique and significant role in supporting goal-directed visual information processing in the primate brain.