Pattern‐evoked responses and luminance‐evoked responses in the human electroretinogram.

Abstract

Electrical potentials were recorded from the cornea of the human eye in response to the onset and offset of square‐wave stripe patterns varying in spatial frequency, luminance and contrast. Under high retinal illumination (50119 photopic td) the response to pattern onset was a positive wave (pattern‐onset wave) followed by a negative after‐potential. As long as the pattern was presented, a steady potential of positive polarity (plateau potential) was observed. The response to pattern offset was a biphasic negative‐positive wave followed by a negative after‐potential. A comparison between wave forms obtained with pattern onset‐offset stimuli and luminance increase‐decrease stimuli suggests: (a) the pattern‐onset wave is the result of an interaction between a luminance‐increase and a luminance‐decrease response; (b) the plateau potential is mainly an additive superposition of two receptor processes originating from retinal areas that receive increases and decreases in local luminance; (c) the negative‐positive potential is an a‐wave and a b‐wave originating from retinal areas that receive increases in local luminance. The amplitude of the pattern‐onset wave was greatest at a spatial frequency around 3‐4 c/deg. This behaviour was closely correlated with contrast sensitivity determined psychophysically by previous investigators. Therefore, the pattern‐onset wave seems to be a pattern‐evoked response. The amplitude of the b‐wave following pattern offset showed a monotonic decrease with increasing spatial frequency. It is mainly a luminance‐evoked response. Under low retinal illumination (457 photopic td) the pattern‐onset wave and the b‐wave at pattern offset were smaller. However, the pattern‐onset wave had its maximum amplitude at a lower spatial frequency. When increases or decreases in space‐average luminance were combined with pattern onset or offset, transitions between pattern‐ and luminance‐evoked responses could be observed. The results suggest that a decrease in local luminance is the essential stimulus for evoking a pattern‐related response while increases in local light intensity generate luminance‐evoked responses.