In cluttered natural visual environments object recognition capacity can be severely limited. This may reflect limitations associated with the visual cortical encoding of multiple nearby stimuli. Alternatively, poor object recognition in clutter, especially profound in patients with autism, may result from limited resolution of attentional control and object decoding that rely on interactions between visual cortex and frontal cortex. We do not know what neuronal mechanisms limit object recognition in crowded scenes because neurophysiological studies typically present one or two stimuli at a time, and are thus free from the constraints imposed by clutter in natural scenes. In addition, studies seldom investigate the role of visual-frontal interactions in object recognition. We will use a combination of single neuron studies in awake monkeys, behavioral manipulations, reversible inactivation and computational modelling in two mid-level stages of visual cortex, V2 and V4, and the prefrontal cortex (PFC), to determine:
(Aim 1) how V2 and V4 neurons encode visual stimuli in the presence of clutter, and how the encoding depends on eccentricity and on attentional engagement;
(Aim 2) how PFC feedback influences encoding in V2 and V4, and how these brain regions together contribute to shape discrimination in clutter. We will consider three hypotheses. First, visual encoding may have limited resolution in clutter: when many objects are nearby, regardless of what those objects are, the visual system may fail to segment and encode individual objects. Second, processing in mid-level stages may be designed to encode only salient objects, i.e., objects that exhibit sufficient feature contrast relative to neighboring image regions. In this case, loss of information may pertain to objects in homogeneous image regions reflecting a representational strategy to preferentially encode objects that stand out. Third, it is possible that all objects are segmented and encoded faithfully, even in clutter, but the capacity limits are dictated by the resolution of attention or other downstream processes that influence object decoding. Our studies will address a fundamental gap in the understanding of how multi-objects displays, which dominate natural vision, are encoded in mid-level visual cortex. They will reveal how encoding strategies vary across eccentricity and this could be relevant for diseases like age-related macular degeneration, where foveal representations are compromised selectively. Finally, our results will provide fundamental insights into how V4 and PFC communication is critical for object recognition in clutter and how diminished communication between the two could influence behavior. This could be important for guiding translational work on autism spectrum disorder.
We will use a combination of primate neurophysiology experiments, computational modeling, animal behavior and reversible inactivation methods, to achieve a new level of understanding about how cluttered visual displays are encoded in visual cortex and how interactions between visual cortex and prefrontal cortex facilitate object recognition in clutter. These findings will ultimately bring us closer to devising strategies to alleviate and treat brain disorders of impaired object recognition resulting from dysfunctions in the occipito- temporal pathway (e.g. agnosia) and from diminished communication between visual and prefrontal cortex (e.g. autism).
| Choi, Hannah; Pasupathy, Anitha; Shea-Brown, Eric (2018) Predictive Coding in Area V4: Dynamic Shape Discrimination under Partial Occlusion. Neural Comput 30:1209-1257 |
| Oleskiw, Timothy D; Nowack, Amy; Pasupathy, Anitha (2018) Joint coding of shape and blur in area V4. Nat Commun 9:466 |
| Fyall, Amber M; El-Shamayleh, Yasmine; Choi, Hannah et al. (2017) Dynamic representation of partially occluded objects in primate prefrontal and visual cortex. Elife 6: |
| El-Shamayleh, Yasmine; Pasupathy, Anitha (2016) Contour Curvature As an Invariant Code for Objects in Visual Area V4. J Neurosci 36:5532-43 |
| Pasupathy, A (2015) The neural basis of image segmentation in the primate brain. Neuroscience 296:101-9 |
| Oleskiw, Timothy D; Pasupathy, Anitha; Bair, Wyeth (2014) Spectral receptive fields do not explain tuning for boundary curvature in V4. J Neurophysiol 112:2114-22 |
| Kosai, Yoshito; El-Shamayleh, Yasmine; Fyall, Amber M et al. (2014) The role of visual area V4 in the discrimination of partially occluded shapes. J Neurosci 34:8570-84 |
| Yau, Jeffrey M; Pasupathy, Anitha; Brincat, Scott L et al. (2013) Curvature processing dynamics in macaque area V4. Cereb Cortex 23:198-209 |
| Bushnell, Brittany N; Pasupathy, Anitha (2012) Shape encoding consistency across colors in primate V4. J Neurophysiol 108:1299-308 |
| Bushnell, Brittany N; Harding, Philip J; Kosai, Yoshito et al. (2011) Equiluminance cells in visual cortical area v4. J Neurosci 31:12398-412 |
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