The activity of V4 in free viewing visual search

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DESCRIPTION (provided by applicant): When viewing the natural world, primates use saccadic eye movements to scan the environment and fixate on objects of interest for maximal visual processing. However, since there are many potential objects of interest in the visual scene, choosing a saccade target is crucial. Selection of an eye movement to a particular item is based on a topographic map representing the salient world. Lateral intraparietal cortex (LIP) might construct this salience map since this visuomotor area can localize a behaviorally relevant object for a gaze shift and projects to areas involved in executing eye movements. However, LIP lacks the visual form processing necessary to guide purposeful saccadic behavior to a particular object based on its features. On the other hand, V4 is an excellent candidate as a visual area capable of selecting saccade targets. It is an extrastriate cortex responsible for object processing, has activity correlated to eye movements and sends direct projections to LIP. Thus, we propose that area V4 provides the visual input for the salience map represented in LIP which guides saccade patterns characterized by natural vision. The main objective of this experiment is to characterize the physiological response properties of V4 neurons during free viewing visual search to better understand the role they play in more natural visual processing. We designed a free viewing visual search task where monkeys are entirely free to move their eyes and report the results of the task by making a non-targeting hand movement. We will examine oculomotor behavior and neural activity recorded from single V4 and LIP cells while the monkeys perform this task to investigate the following 3 aims: 1) We will characterize the presaccadic activity of V4 neurons to describe their contribution to guiding subsequent saccades. 2) We will look at the mechanisms V4 uses to identify a behaviorally relevant saccade target based on object features. 3) We will test the function of the connection between V4 and LIP. By exploring the relationship between V4 and LIP in this identical task, we can understand better the link between visual form processing and selection of the eye movement to ultimately locate a search target during natural vision. HEALTH RELEVANCE: Patients with parietal and occipital lesions have difficulty in visual perception and generating eye movements. By understanding the physiology underlying normal functioning visual behavior, we can better diagnose and design rehabilitation programs for these patients.