PERCEIVED CONTRAST AS A FUNCTION OF ADAPTATION DURATION

The measured how the perceived contrast of a sinusoidal grating fades as a function of time. Measurements were made for a range of temporal and spatial frequencies and eccentricities. Patterns of high temporal and low spatial frequency exhibited a greater and more rapid loss of a pparent contrast (fade) than those of medium frequencies. The rate and amount of fading for a subgroup of moderate frequencies increased whe n presented peripherally rather than foveally. Further measurements re vealed that gratings of disparate spatial frequencies, but with the sa me threshold sensitivity, exhibit very different fading characteristic s but equal threshold elevation. We conclude that the differential los s of apparent contrast is not an artefact of differing proximities to threshold, nor can it be accounted for by differences in the adaptabil ity of underlying spatio-temporal mechanisms at threshold. The differe nces in fading may thus reflect either a difference in the adaptabilit y of underlying channels above threshold or a differential contributio n of such channels to perceived contrast.