Visual-evoked response produced by patterned light stimulus.

The photopic visual-evoked response (VER) produced by patterned stimuli was examined by changing: (1) the stimulus magnitude, (2) the contour density of the test pattern, and (3) the contour contrast. In the majority of normal subjects the VERs obtained by a grating pattern showed their maximum response at a relatively low level of stimulus magnitude. With a logarithmic increase in contour density of the test pattern, the response amplitude increased in almost linear fashion. The VERs to the multiple-hole pattern of different contrast showed an S-shaped increase of the amplitude with an increase of log contrast. The latency of these VERs showed very small change when contour density or contrast was changed. The results suggested that there were two different components in the VER. The one was due to the light sensitivity and the other was due to the contrast sensitivity in the visual system. The latter seemed to be dominant in the photopic VER.