Abstract
Filling-in can be induced by high-contrast edge adaptation (Shimojo & Kamitani VSS'01), or after prolonged adaptation to a peripheral low-contrast object (Troxler 1904). Adaptation to sustained low-contrast vs. adaptation to transient high-contrast suggests synergy between contrast and edge adaptation, but the possible interactions are not well understood. We observed that presenting a low-contrast edge for 5–10 seconds and then flashing a high-contrast edge over it could elicit the perceptual disappearance of a subsequent low-contrast edge at the same location. Neither adaptation to the low-contrast edge nor flashing the high-contrast edge alone had any significant effect. We investigated this effect using Gabor signals (2 cpd, 5 deg eccent., sd=1, mean lum. 50cd/m2, background 50cd/m2). Target (contrast=4%) followed either a) a sustained (8 sec) low (4%) contrast stationary or drifting Gabor signal (adaptation only), b) a brief (20ms) high (∼100%) contrast Gabor signal (flash only), or c) adaptation followed by flash (combined condition). A random-dot mask followed the target after 1 second. The task was to identify whether the target was present or not. Subjects (n=5) failed in less than 3% of the trials in adaptation only or flash only conditions, but more than 30% in the combined condition (p<.0001). For combined condition trials, failure of detection was more pronounced after adaptation to a drifting Gabor than a stationary one (p<.05). There was no significant difference between same or opposite contrast polarity (phase insensitivity). In other experiments we found: a) suppression is selective for orientation, and b) disappearance could be transferred to other locations. Results suggest 1) Contrast gain adjustment to transient change is processed separately from adaptation to sustained stimuli; 2) the two mechanisms interact non-linearly. Findings are compatible with non-local orientation selective cortical mechanisms presumably at the level of V1 to V4.