The human visual system rapidly, accurately, and seemingly effortlessly, recognizes objects that are partially occluded. The long-term goal of research in my laboratory is to determine how this is achieved by the primate visual system. Previous research has demonstrated that visual information that reaches our eyes is processed along the multi-stage ventral "shape processing" pathway. We will investigate the contributions of area V4, an intermediate stage in this pathway, to the processing of partial occlusion. When the three-dimensional world casts a two-dimensional image on the retina, objects that are closer to the viewer partially or completely occlude objects that are farther away. This causes two types of distortions in the retinal image. First, partial occlusions produce "accidental" contour features due to the accidental juxtaposition of the bounding contours of the occluded and occluding objects. Second, parts of the occluded object are missing and may even be fragmented in the retinal image. To accurately recognize the occluded object despite partial occlusion, the visual system needs to discount the accidental contour features and then sew together the fragmented parts by amodally completing the missing contours. Psychological and theoretical evidence suggests that analysis of image features at the intersecting junctions of the occluded and occluding contours (T-like junctions) in the early stages of visual processing underlies processing of occlusion but the neural mechanisms are unknown. Evidence from lesion studies and neurophysiological studies suggest that area V4 is likely to play an important role. A competing hypothesis proposes that occlusion is inferred as a result of robust recognition of objects from their fragmented parts in the highest stages of processing such as inferotemporal cortex. The two hypotheses make distinct predictions about the patterns of responses in area V4. We will conduct single cell recordings of V4 neurons in awake primates performing fixation and behavioral tasks.
In aim 1, we will investigate if V4 responses support differential processing of real and accidental contour features.
In aim 2, we will investigate if amodal completion signals in area V4 appear before or after accurate recognition of the partially occluded object. Results from these experiments will determine which of the above hypotheses is supported in the primate brain. It will also identify V4 neural mechanisms that contribute to inference about partial occlusion. Object recognition is impaired in visual agnosia, a dysfunction of the occipitotemporal pathway. Results from the proposed experiments will constitute a major advance in our understanding of the brain computations that underlie object recognition and will bring us closer to devising strategies to alleviate and treat this brain disorder.
Object recognition is a fundamental capacity of the human brain essential for our interaction with others and for all complex behavior in general. This fundamental brain function is impaired in visual agnosia, a dysfunction of the occipitotemporal pathway. Results from the proposed experiments will constitute a major advance in our understanding of the brain computations that underlie object recognition and will bring us closer to devising strategies to alleviate and treat this brain disorder.
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