This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. The goal of research in my laboratory is to understand how the form and color of visual stimuli are encoded in the neural activity patterns in the visual cortex and how this representation underlies perception and object recognition. We have just published the results from the first set of experiments in the laboratory which investigate how partially occluded objects are encoded in the primate brain. In everyday situations, objects are often partially occluded. But, despite retinal image distortions caused by partial occlusion, our visual system recognizes objects robustly and efficiently. To investigate how this is achieved, we studied the responses of neurons in area V4, an intermediate stage in the shape processing pathway. Our results indicate that V4 responses more closely resemble the perceived stimulus than the retinal stimulus, i.e. V4 neurons do not encode contours that are likely to arise in the retinal image as a result of partial occlusion. Our results provide insights into which contours are encoded in the visual scene and how V4 responses might contribute to robust perception. In a second experiment, we are studying the activity of V4 neurons as the animal is engaged in a shape matching task. Our results indicate that the early activity ( 200ms after stimulus onset) of roughly 50% of V4 neurons is strongly correlated with behavior. Further, animal behavior is significantly correlated with the activity of a third of the neurons. These results suggest that early activity in area V4 might inform object recognition performance. Finally, our investigations into color representation in V4 have revealed a novel class of V4 neuron that responds preferentially to colored stimuli at equiluminance which could play an important role in chromatically-defined contours.
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