Abstract
Prolonged exposure to a high contrast stimulus reduces the neural sensitivity to subsequent similar patterns. Recent work has disclosed that contrast adaptation is controlled by multiple mechanisms operating over differing timescales (Bao and Engel, 2012; Bao, Fast, Mesik, & Engel, 2013). Adaptation to high contrast for a relatively longer period can be rapidly eliminated by adaptation to a lower contrast (or meanfield in the present study). Such rapid deadaptation presumably causes a short-term mechanism to signal for a sensitivity increase, canceling ongoing signals from long-term mechanisms. Once deadaptation ends, the short-term mechanism rapidly returns to baseline, and the slowly decaying effects in the long-term mechanisms reemerge, allowing the perceptual aftereffects to recover during continued testing. Although this spontaneous recovery effect is considered strong evidence supporting the multiple mechanisms theory, it remains controversial whether the effect is mainly driven by visual memory established during the initial longer-term adaptation period. In Experiment 1, adapting stimuli were either visible or rendered invisible with a modified Continuous Flash Suppression (CFS) paradigm. We used a contrast matching task to track the dynamic of effects of adaptation. We found reliable spontaneous recovery emerging rapidly in the initial phase of the post-test for both visible and invisible adapters. In Experiment 2, the adapting grating was either displayed alone or flanked by other similar gratings (i.e. a 'crowding' paradigm introduced by He, Cavanagh, & Intriligator, 1996). The time course of contrast detection thresholds were tracked on the same purpose. Spontaneous recovery was found not only in the adapter-alone condition but also in the crowded condition (orientation indiscernible). These results exclude the possibility that spontaneous recovery found in the previous work is merely the consequence of explicit visual memory. Our findings also demonstrate that contrast adaptation, even at the unconscious processing levels, is controlled by multiple mechanisms.
Meeting abstract presented at VSS 2016