We used a hue-scaling task to examine changes in color perception resulting from adaptation or induction to color contrast in spatially-varying backgrounds. Observers judged the perceived color of tests after or while viewing backgrounds composed of color differences along selected axes in color space. Both contrast adaptation and contrast induction produced large and selective shifts in perceived hue angle, and interacted in similar ways when combined, suggesting that they had functionally similar influences on perceived hue. Both also consistently biased perceived hue away from the color axis of the background, implying response changes within multiple channels tuned to different directions in color space. Selective hue changes were also observed when the gamut of colors forming the backgrounds were drawn from natural color distributions. This suggests that color perception in different environments may be systematically biased by adaptation to the distributions of colors in those environments. However, we did not find these biases when the same test stimuli were judged after adapting to actual natural scenes.
After observers have adapted to an edge that is spatially blurred or sharpened, a focused edge appears too sharp or blurred, respectively. These adjustments to blur may play an important role in calibrating spatial sensitivity. We examined whether similar adjustments influence the perception of temporal edges, by measuring the appearance of a step change in the luminance of a uniform field after adapting to blurred or sharpened transitions. Stimuli were square-wave alternations (at 1 to 8 Hz) filtered by changing the slope of the amplitude spectrum. A two-alternative-forced-choice task was used to adjust the slope until it appeared as a step change, or until it matched the perceived transitions in a reference stimulus. Observers could accurately set the waveform to a square wave, but only at the slower alternation rates. However, these settings were strongly biased by prior adaptation to filtered stimuli, or when the stimuli were viewed within temporally filtered surrounds. Control experiments suggest that the latter induction effects result directly from the temporal blur and are not simply a consequence of brightness induction in the fields. These results suggest that adaptation and induction adjust visual coding so that images are focused not only in space but also in time.
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