Binocular interaction and steady-state visual evoked potentials. I. A study in normal subjects and in subjects with defective binocular vision.

A correlate of binocular-neuron activity was found in some properties of visual evoked potentials (VEPs), such as facilitation (defined as a binocular response greater than the sum of the monocular responses) and changes in latency (shortening of binocular VEP latency as compared to that of monocular VEPs). Monocular and binocular steady-state VEPs in response to phase-alternating gratings of different contrast and both spatial and temporal frequency were recorded in three normal subjects. Fourier analysis of the responses was performed to isolate the component at the reversal frequency. Binocular VEPs showed facilitation in the low-contrast range (3%-10%). Facilitation was highest for gratings that had spatial frequency of 0.6-2 cycles/degree (c/d), alternating at 16 reversals per second. Phase shortening was found across a parameter range larger than that at which amplitude facilitation occurred. These results suggest that both amplitude facilitation and phase shortening in binocular VEPs may provide an objective measure of binocular visual function in clinical ophthalmology.