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 goal of research in my laboratory is to understand how visual stimuli are encoded in the neural activity patterns in the visual cortex and how this representation underlies object recognition. In one set of experiments we are investigating how partially occluded objects are encoded. In everyday situations objects are often partially occluded but our visual system recognizes objects robustly and efficiently despite retinal image distortions due to partial occlusion. To discover how this is achieved in the primate brain, we have conducted experiments in two fixating monkeys to study activity in area V4 and compare representations when an object is isolated versus when adjoined by a contextual stimulus that suggests partial occlusion. Our results indicate that responses of V4 neurons more closely resemble the perceived stimulus, i.e. V4 neurons do not encode contours that are likely to arise in the retinal image as a result of partial occlusion. In a second experiment, we have trained an animal to perform a shape matching task in the presence of occluders. We will start recording from this animal in a few weeks to study activity of V4 neurons as the animal performs the task. Correlation between neural activity and animal behavior on a single trial basis will provide important insights into how V4 activity is utilized for recognizing objects. Finally, we have found a new class of cells in V4 that respond preferentially to colored stimuli at isoluminance. When the contrast between the stimulus and background increases the neuron is suppressed. We are currently investigating how this neuron contributes to color perception.