Abstract
Adaptation to contrast elevates contrast detection/discrimination thresholds and reduces apparent contrast. The study of binocular contrast adaptation over the past 50 years has focused on the relative effect of adapting and testing to the same compared to opposite eyes in order to yield a measure of interocular transfer (IOT), a protocol that only involves monocular adapting and test stimuli. However a full characterization of binocular adaptation requires measurements of binocular as well monocular adapting and test stimuli. Using 3.6 cpd grating stimuli we measured threshold versus contrast (TvC) functions for the full gamut of combinations of monocular and binocular adapting and test stimuli. For each combination of adapt/test eye(s), the adapted TvC data followed the classic 'dipper' curve similar to the unadapted data, but displaced obliquely to higher contrasts. Adaptation had effectively re-scaled all contrasts by a common factor Cs that varied with the combination of adapt and test eye(s), an example of contrast gain control. Cs was well described by a simple 2-parameter model that had separate gain controls, sited before and after binocular summation respectively. When these 2 levels of adaptation were inserted into an existing model for contrast discrimination, the extended 2-stage model gave a good account of the TvC functions, their shape invariance with adaptation, and the contrast scaling factor.