NEURAL BASIS OF SHAPE REPRESENTATION AND RECOGNITION

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The visual system rapidly and accurately 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. Under natural viewing conditions, visual objects that are closer to the viewer partially or completely occlude objects that are farther away. This produces "accidental" contour features due to the juxtaposition of the bounding contours of the occluded and occluding objects. Secondly, 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. Preliminary results from our laboratory suggest that responses of V4 neurons in awake primates differentially represent real and accidental contours. Amodal completion signals in area V4 also appear before accurate recognition of the partially occluded object. These results strongly support the hypothesis that area V4 is crucial for recognition under partial occlusion. Object recognition is impaired in visual agnosia, a dysfunction of the occipitotemporal pathway. Results from these 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.