Binocular interaction in the VEP to grating stimulation. I. Orientational effects.

The orientational effects of monocular stimulation with sinusoidal grating patterns were studied with transient VEP technique in 10 subjects with normal vision and binocular functions. No significant variation in amplitude with orientation was obtained. The latency for 45 degrees (oblique) orientation was slightly longer than the latency for other orientations. The orientational effects on binocular interaction in dichoptic stimulation were determined with sinusoidal grating patterns at a reversing rate of 1.9 and 2.1 Hz for each eye respectively. The binocular interaction was assessed as the binocular/monocular ratio of the VEP amplitude for each eye. There was a significantly reduced binocular interaction for dichoptically presented perpendicular gratings as compared to parallel gratings at the spatial frequencies of 2, 4 and 6 cycles/degree, when mean values of the whole group of subjects were statistically analysed. A broad orientation tuning of about 45 degree was found for the binocular interaction at 4 cycles/degree for the group as a whole, although tuning was hard to establish in the VEP of each individual. This compares well with other neurophysiological and electrophysiological data but is broader than the orientation tuning demonstrated psychophysically.