Recovery from contrast adaptation matches ideal-observer predictions

Recovery from contrast adaptation was studied in psychophysical experiments. We measured detection thresholds for a test pulse presented on a photopic background as a function of the time after the offset of a high-contrast flicker of the background. The decrease of thresholds with time is well described by a power-law function. Thresholds for tests presented at 640 ms after the offset of the background contrast are still significantly elevated above the threshold measured when the observers have completely adapted to a steady background. We compare the psychophysical data with contrast estimates of ideal-observer models. A match between the results for human and ideal observers can be obtained when the ideal observer is limited by noise. For a quantitative match, we assume that the ideal observer performs a Bayesian calculation on its noise-perturbed input, sampled every 10-20 ms. For the Bayesian calculation we assume a prior probability distribution function for the input contrast that has a lower cutoff at the standard deviation of the noise.