Proceedings of the Annual Meeting of the Cognitive Science Society

In psychophysics, the effects of light backgrounds and photopigment bleaching can be equated in a variety of situations involving sensitivity, flicker, and the subjective perception of brightness. We have investigated such possible equivalences at the single unit level through intracellular recordings from vertebrate rods. At a given level of background or bleaching adaptation, vertebrate rods respond with characteristic waveforms to brief flashes of light of increasing intensity. The peak responses can be plotted vs. flash intensity to give a response curve in each state of adaptation. Two consequences of light adaptation are a shift to higher light intensities and a compression of the response curve. We have been able to establish equivalences in single units between bleaching and backgrounds in terms of threshol delevation and response compression. Moreover, we have found that such equivalent (background, bleaching) pairs have similar response curves. But these response curves are direct measures of stimulus flash intensity . Based on the close parallels between the psychophysical and the neurophysio 1 ogica 1 equivalences of bleaching and backgrounds, we therefore propose that brightnessperception is mediated by the peak responses of photoreceptors. It is not often that behavioral observations can be traced back to the neuronal machinery and the latter suggest psychophysical tests which can further clarify brightness equivalence relations. This approach is discussed in the light of our results.