Monocular and binocular evoked average potential field topography: upper and lower hemiretinal stimuli

Scalp potentials evoked by monocular and binocular 2/s checkerboard reversals with checks of 56 or 14 min were recorded from four midline electrodes between inion and 7.5 cm above inion vs a common anterior reference in 31 normals. The electrode location and latency of the evoked maximal occipitally positive potential difference between any 2 of the 5 electrodes, between 80 and 140 ms latency was determined in each run. Mean maximum locations over subjects for upper hemiretinal, binocular stimuli were more anterior than for monocular stimuli; for lower hemiretinal stimuli, inverted location differences were found. Binocular responses also had shorter latencies than monocular responses. Since area 18 is more anterior to 17 for upper, more posterior to 17 for lower hemiretinal projection to cortex, the results suggest that neurons which respond only if both eyes are simultaneously stimulated are more frequent in higher than lower order visual areas.