Functional properties of neurons in area V1 of awake macaque monkeys: peripheral versus central visual field representation.

The region of the striate cortex where the visual field is represented up to 52 degrees from the fovea was explored in awake, behaving monkeys. Extracellular recordings were made from 241 neurons. On the basis of their receptive field position in the visual field, they were subdivided into a central (within 10 degrees from the fovea) and a peripheral (beyond 10 degrees) group. Sensitivity to orientation, length, direction and velocity of movement of conventional light stimuli was tested and compared in the two samples. Besides the well-known increase of receptive field size with eccentricity, gross differences were found only for the sensitivity to the velocity of stimulus movement. The great majority of neurons in the central sample preferred slow velocities and showed no sensitivity to velocities above 100 degrees/sec. In contrast, many peripheral neurons were poorly sensitive to slow speeds of movement and well responsive to high velocities, above 100 degrees/sec. Cells that showed a better response to an actual stimulus movement in the visual field than to a retinal image movement self-induced by an eye-movement ("real-motion" cells) were also searched for in the two samples. They were found in the 13% of the central neurons and in the 25% of the peripheral neurons. Present data extend to the awake, behaving animal what already known from paralysed animal, indicating that in physiological conditions central and peripheral vision have a different functional role in the analysis of motion within the visual field.