Visual evoked response as a function of grating spatial frequency.

Transient visual evoked responses (VER's) to the appearance-disappearance of sinusoidal gratings have been investigated for a range of spatial frequencies. Contrary to the results of previous studies, the results show that the transient VER consists of a relatively simple waveform that is most easily characterized by the initial negative peak (N1) whose latency and amplitude vary with the contrast and spatial frequency of the grating. At spatial frequencies less than 3 cycles/degree (c/d) an additional short latency component appears in the response. This component is maximum at 1 to 2 c/d, saturates at low contrast, and is insensitive to the precise position of the grating on the retina. The results are related to the properties of transient and sustained channels assumed to exist in the human visual system.