Contrast adaptation and contrast gain control

Electrophysiological measurements have shown that contrast adaptation can increase the contrast gain of cortical cells of the cat and the monkey. This implies that adaptation could enhance the contrast discrimination sensitivity. Psychophysical contrast discrimination experiments were performed with and without contrast adaptation. The stimuli were spatially separated stationary Gabor patterns. The pedestal contrast was varied from 6 to 75 per cent. The spatial frequency was 1.5, 5.0 or 20 cpd. After adaptation the contrast detection thresholds are elevated and the subjective contrast is lowered. The contrast discrimination thresholds remain unchanged.