Contrast adaptation implies two spatiotemporal channels but three adapting processes

The contrast gain control model of adaptation predicts that the effects of contrast adaptation correlate with contrast sensitivity. This article reports that the effects of high contrast spatiotemporal adaptors are maximum when adapting around 19 Hz, which is a factor of two or more greater than the peak in contrast sensitivity. To explain the discrepancy, the predictions made by parallel versus cascaded models of spatiotemporal processing are compared. It is demonstrated that a parallel two-temporal channel model, in which the adaptive attenuation of a channel is proportional to its response, cannot explain the effects of adaptation on threshold contrast but that a cascaded model can. The cascaded model suggests that the visual system temporally encodes spatiotemporal signals via an adaptive transient encoding process that lies in cascade with an adaptable two-temporal channel system of sustained versus transient processes.