Receptive field types of area 18 neurones in the cat.

In cats, 131 area 18 units with receptive fields 10-50 degrees from the visual axis, were recorded and tested with moving stimuli. These stimuli included light slits, dark bars, single edges, gratings and a random square pattern. 94% of the units were responsive to visual motion. 106 neurones could be classified by a screening procedure based on responses to a moving standard grating and a moving random square pattern. When testing with moving stimuli, the criteria for distinguishing between simple and complex cells in area 17 (Pettigrew et al., 1968; Bishopel al., 1971a,b, 1973 Goodwin and Henry, 1975, Sherman et al., 1976) also apply to area 18 neurones. No tests with stationary stimuli were made in distinguishing simple from complex cells. In addition to simple (50%) and complex (18%) cells, area 18 contains other cell types as hypercomplex cells (11%), cells with a radially symmetric RF (6%) and amplitude specific cells (10%). Six cells (5%) were unclassified. A special battery of tests was designed to study the RF of the very sophisticated amplitude specific cells. Their RF appears to consist of a discharge region preceded by a trigger area and of two flanking inhibitory regions.