Foveal and extrafoveal influences on the topography of the visually evoked, early negative potential in man

Abstract

Variations in topographic characteristics of the early negative potential of the human, flash-evoked cerebral response were related to (1) a graduated series of stimulus sizes subtending visual angles from 1[deg] to 32[deg], and (2) a graduated series of central opacities subtending visual angles from 1[deg] to 16[deg] placed within a 32[deg] stimulus.The longitudinal field pattern of the early negative potential was shown to be a function of the spatial characteristics of the visual stimulus. Foveal stimulation produced a local, early negative potential in the occipital region, generally associated with surface-positive activity anteriorly, whereas peripheral stimulation gave a widespread early negative potential, relatively less prominent in the occipital region than in preoccipital areas. Intermediate field-gradient configurations resulted from various combinations of foveal, parafoveal and peripheral stimulation.The effect of addition of extrafoveal to foveal stimulation upon the magnitude of the occipital early negative potential proved to be subject-dependent.