A Model for the Fading of Stabilized Images in a Visual System

A multiplicative gain control mechanism to account for the gradual fading of a stabilized image, the off-image, and the phenomenon of apparent contrast reversal is proposed. This phenomenon occurs when a uniform increment is added to a fading image. Fading and time-to-disappearance are examined as functions of contrast, spatial frequency, and average luminance. Contrast threshold for off-images is also derived. Predictions of the model are compared to data when available. It is shown that this multiplicative model predicts a recent observation that the difference between contrast "thresholds" under stabilized and unstabilized conditions is equal to the contrast of the off-image produced by a stimulus whose contrast equals the stabilized contrast "threshold." An additive model is also investigated and shown to be incapable of accounting for some of the phenomena.