.) Recently, considerable progress has been made in understanding the brainstem mechanisms involved in ocular vergence and lens accommodation, two of the three components of the highly integrated 'near response.' This work has emphasized the inadequacies of our knowledge of how information related to depth is processed and transmitted to the brainstem oculomotor areas. Clearly, the sensory processing of cues to depth utilizes primary visual cortex. Many striate and prestriate neurons in the monkey are sensitive to binocular disparity and the high spatial frequencies necessary for accurate binocular alignment and the adjustment of accommodation. Beyond this however, our understanding of the cortical mechanisms of perceptual and oculomotor responses related to depth is fragmentary. There are clear indications that posterior partial cortex may be involved in some of the processing of this information. Studies of lesions in humans have demonstrated deficits in both the perception of depth and in oculomotor responses to visual targets in depth. Recent neurophysiological studies in posterior parietal cortex of monkeys have shown that some neurons respond selectivity to target depth or to the oculomotor response associated with these targets. Anatomically, posterior parietal cortex receives input from prestriate visual areas and sends projections into the midbrain and pons. This project will consist of a series of neurophysiological experiments in behaving primates to investigate the involvement of parietal cortical neurons in visual-motor behavior in the depth dimension. Monkeys will be trained to fixate and follow visual targets while the responses of individual neurons to the visual stimulation and the motor behavior is investigated. Several behavioral tasks will be employed using a specialized visual display and recording apparatus which will allow independent control and measure of important aspects of the sensory and motor parameters. Specifically, the relation of the neurons to stimulus form, position, motion binocular disparity and accommodative demand will be determined; as well as to the parameters of binocular eye position and velocity, and to lens accommodation. Elucidation of basic mechanisms of parietal function related to depth perception and to disjunctive eye movements is likely to provide valuable insights into the disorders involving disease of the parietal cortex and into the neurology of the motor control of the near response triad in general.
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