Analysis of the Effect of Pattern Adaptation on Pattern Pedestal Effects: A Two-process Model

Pattern contrast thresholds for vertical Gabor patterns were measured on pattern pedestals that
were vertical or horizontal. Contrast of the pedestal was varied to measure the function relating target contrast threshold to pedestal contrast (TvC function). TvC functions were measured
without an adaptor & after adaptation to vertical, horizontal & plaid patterns. For a pedestal with the same orientation as the target, the vertical & plaid adapters increased thresholds at lown pedestal contrasts, but not high. For the pedestal orthogonai to the target, the same two adaptors increased thresholds over the whole range of pedestal contrasts. These asymmetric effects are
described by a model of adaptation & masking derived from a model of masking (Foley, 1994a) by
allowing two parameters to vary with the adapt state; one of them is an additive parameter in the denominator of the response function, which can be interpreted as adaptor-produced divisive
inhibition that persists after adaptor offset; the other is the sensitivity to pedestal-produced divisive inhibition, which is changed by adaptation for the pedestal orthogonal to the target. Other models do not account for both effects.