Effects of stimulus contrast on binocular VER.

The effect of stimulus contrast changes on the binocular visual evoked response (VER) was investigated using pattern reversal VER, dichoptic stimulation, and Fast Fourier Transform. When the stimulus contrast was changed binocularly, the monocular components increased as the contrast increased. The binocular component first appeared at the level of 10% contrast; its magnitude was stable under all recording conditions. When the stimulus contrast was changed monocularly, the eye that received the higher contrast stimulation showed more power in the power spectrum. The binocular component appeared even when the difference in contrast between the two eyes was large. The magnitude of the binocular component was stable under all recording conditions. We concluded that the binocular and the monocular components differ in the magnitude of their responses to a contrast change and speculate that the pathways responsible for the two components are not identical.