1. About 10% of a sample of 436 cells recorded in the retina of macaques had receptive fields lacking a center-surround organization. These cells had a diffuse extrafoveal distribution, they were less frequently found in the foveal region, and their conduction latencies overlapped with those of cells (types I, III, and IV) having a center-surround organization. Three groups were distinguished. 2. Type II cells had spectrally opponent responses mediated by mechanisms having similar or identical distributions and response latency; these cells did not respond to white light. They predominated in the central retina, they usually received input from all three types of cone, they had a linear spatial summation of incomming photo-receptor signals, they lacked rod input, they had conduction latencies that were intermediate between those of the other two groups, and they could be antidromically activated by electrical stimulation of the lateral geniculate body but not of the superior colliculus. 3. Type V cells were neurons whose common characteristic was the presence of on-off responses to both small and large stimuli. One subgroup had either excitatory or inhibitory on-off responses and a silent inhibitory surround that tended to suppress cell responses and maintained activity. They were observed throughout the central retina, including the fovea; they received input from green- and red-sensitive cones, but not from blue-sensitive cones; they had a non-linear spatial summation; they had comparatively long conduction latencies; and they could be antidromically activated by electrical stimulation of either the lateral geniculate body or superior colliculus. Another subgroup lacked spontaneous activity and any type of surround. They were encountered at a retinal depth more sclerad than that of other neurons and could not be antidromically driven from the optic tract or more central structures; these cells also lacked input from blue-sensitive cones and had a nonlinear spatial summation. 4. Type VI cells were predominantly inhibited by moving stinuli in any direction of motion and failed to respond to stationary flashing stimuli; they appeared to predominate toward the perifovea and had comparatively short conduction latencies.
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