The goal of this research is to analyze the effects of eye movements and eye position on the electrical activity of neurons in primary visual cortex (VI) and the second visual cortical area (V2) of macaque monkeys. During the viewing of natural scenes the brain must separate the modulatory influences of eye movements from the signals that code properties of objects in the world. A major theme is the effects of the drifts and the small saccades of fixational eye movements. These miniature eye movements help to maintain the visibility of stationary visual stimuli. Some cortical cells appear to respond preferentially to the slow component of fixational eve movements (drifts) while others respond to the faster component (saccades). For comparison, the effects of larger voluntary saccades that scan the visual world will be studied. Recent psychophysical evidence indicates that voluntary saccades selectively suppress the visual input of the magnocellular system. These results imply that as saccades become larger, there may be a switch from excitatory to inhibitory effects on cortical neurons. In addition, large saccades have the consequence of taking the eye to a new position in the orbit. To judge the position of objects in the world, the brain must maintain information about the position of the eye in the orbit to combine it with location of the image on the retina. The spatial gain fields of V1 and V2 neurons that contribute to this computation will be measured. Recording sites will be localized to specific anatomical compartments to identify the regional networks and the pathways within which the recorded neurons are embedded. The results will be relevant to human visual perception, as well as in vivo imaging of human visual function.
