Steady-state VECPs to foveal and parafoveal stimulation of the upper hemiretina.

Visually evoked cortical potentials were recorded to foveal and parafoveal stimulation of the upper hemiretina using steady-state pattern reversal. The peak distribution on the scalp was located more anteriorly, and the amplitudes were lower for parafoveal than for foveal stimulation. There was a phase lag between foveal and parafoveal stimulation of about 2/5 . pi without affecting the apparent latencies which turned out not to be significantly different. Thus, the generators of the steady-state visual-evoked cortical potentials in response to foveal and parafoveal stimulation are similar to those with transient stimulation.