Effects of spatial frequency and orientation on visually evoked cortical potentials.

Visually evoked cortical potentials (VECP) were recorded from an array of 4 electrodes along the midline over the occipital cortex in 10 normal subjects. Grating stimuli of different spatial frequencies were presented on a circular test field and spatial tuning curves and potential distribution evoked by vertical, horizontal and oblique stimuli were compared. The peak latencies were the shortest for the stimuli of 2.3 cycles per degree grating oriented vertically. The peak latencies increased for horizontal and further for oblique gratings. The effects of spatial frequency or orientation on the location of the major positive components of the VECP were not significant when recorded on the midline scalp.