CEREBRAL CORTICAL MECHANISMS FOR EYE MOVEMENTS AND VISUAL ATTENTION

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Two different lines of inquiry were followed to determine how the cerebral cortex and its efferent regions control eye movements and visuospatial attention. In one, activity of neurons in the posterior cingulate were studied during various visuomotor tasks to determine their activity with respect to eye movements, visual stimuli, and orbital position. Neurons were found which discharged after saccadic eye movements. Their discharge was influenced by the saccade amplitude and direction, the initial orbital position of the eye, and the orbital position of the eye after the completion of saccadic eye movements. Some neurons could also be modulated by changes in background illumination; others had frank visual responses. In the other line of inquiry, visual neurons in the lateral intraparietal region of the cerebral cortex and superior colliculus were studied using the visual stimulation engendered by eye movements in order to understand the effect of motor planning on the visual responsiveness of these neurons. Neurons were also studied in a number of behavioral paradigms to understand the relation of spatial processing to visual processing. Neurons in the lateral intraparietal region discharge in response to visual stimuli give enhanced responses to attended stimuli but also discharge before saccades made without visual stimuli. They effect an accurate representation of space in a retinotopic framework by transiently shifting retinal receptive fields before saccades.