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

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.