Abstract
Adapting to sinusoidal gratings selectively reduces contrast sensitivity to subsequent test stimuli (1). To investigate the perceptual processes underlying selective adaptation, we developed an external noise plus adaptation paradigm and a theoretical framework based on a noisy observer model. After adapting to a 45 deg, 2 Hz counter-flickering sine grating of 0.8 contrast, observers performed two-interval-forced-choice detection of Gabors of matched spatial frequency, tilted either at 45 or 135 deg, and embedded in one of six levels of external noise. Each session began with 2 min of adaptation, and test trials included 6 sec of re-adaptation and two 133 ms test intervals. The psychometric functions for tests of 45 deg without adaptation, and 135 deg with and without adaptation essentially overlapped. The tests of 45 deg after adaptation produced a 92.5% and a 90.8% threshold increase in the zero and highest external noise conditions. A contrast-gain control perceptual template model (cgcPTM) was developed and tested. The cgcPTM consists of a perceptual template, transducer non-linearity, contrast gain control, pre- and post gain control internal noises, and a decision structure. At the overall input and output level, the cgcPTM is mathematically equivalent to an earlier version of the PTM that uses multiplicative noise in place of contrast gain control (2). In either framework, adaptation selectively reduces the gain of the perceptual template at the adapted spatial frequency and orientation without altering either pre- or post gain control (additive and multiplicative) noises, or changing transducer nonlinearity. The theoretical framework and the inferred mechanism of adaptation are fully consistent with the theory of adaptation proposed by Wilson & Humanski (3). We conclude that adaptation selectively reduces the sensory gain to the adapted stimuli.
1.
BlakemoreCampbellJ.Physiol'69;
2.
LuDosherJOSA'99.
3.
WilsonHumanskiVR'93.