Forward pattern masking and adaptation: effects of duration, interstimulus interval, contrast, and spatial and temporal frequency.

Eight experiments are described that compare pattern adaptation and forward pattern masking by examining the effects of five variables on the contrast threshold of a target presented after an adapter or masker. The target is a Gabor pattern with a center frequency of 2 c/deg and a duration of 33 msec. Thresholds are determined using an adaptive spatial forced-choice method. Principal results are as follows. (1) An adapt-refresh regime with a 2 sec refresh and a 2 sec recovery period on each trial is shown to maintain constant performance. (2) Desensitization is very rapid, reaching near maximum in < 200 msec. (3) Recovery is very rapid during the first 100-200 msec and then very slow with the rate of slow recovery decreasing as adapter/masker duration increases. (4) Threshold vs contrast functions are step-like for certain frequency pairs. (5) Sensitivity vs frequency functions derived from adapting and masking are similar in form. (6) Masker temporal frequency (0-15 Hz) has very little effect. These results are described by a theory that postulates that the target is detected by a few mechanisms that are differentially tuned to spatial frequency. The effect of both a forward masker and an adapter is to desensitize the mechanisms that respond to it. Recovery is a weighted sum of two decay processes, one fast and one slow. The theory fits the data from both paradigms well with some differences in parameters.