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Sae Kaneko, Ikuya Murakami; Simultaneous contrast of brightness and color for flashed stimuli. Journal of Vision 2011;11(11):366. doi: 10.1167/11.11.366.
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Perceived brightness and color are affected by surrounding luminance and color. This simultaneous contrast has been thought to involve a slow process, on the grounds that the effect from a temporally modulated annulus disappears at modulation rates higher than 3–5 Hz. We investigated whether the simultaneous contrast was seen in a briefly flashed stimulus by measuring the brightness of a mean-luminance gray test disk (radius 0.5 deg). On a mean-luminance gray background, an annulus centered at the disk was presented for one frame of a CRT display or for 500 ms, whereas the luminance of the disk remained constant. The luminance of the annulus was varied (0–66 cd/m2). Subjects were asked to adjust the luminance of a comparison disk of the same size (surrounded by luminance noise) to match its brightness with that of the test disk. Not only was a simultaneous contrast effect induced from the flashed annulus, but also it yielded a stronger illusion than the longer-lasting annulus. This enhancement was weakened when a spatial gap was introduced between the disk and annulus. The enhancement of simultaneous contrast was also found in equiluminant colors. The color of the annulus was manipulated in eight directions from the central achromatic point on an equiluminant plane in DKL color space, and subjects were asked to match the hue and saturation of a comparison disk with those of the physically gray test disk embedded within the annulus. In all chromatic directions, the flashed annulus similarly led to a stronger illusion than the longer-lasting annulus, suggesting that the enhancement effect involves an early stage of visual processing, e.g., at LGN. We conclude that the simultaneous contrast is not necessarily mediated by a slow process, and discuss the temporal properties of simultaneous brightness/color contrast in relation to existing models of early visual encoding.
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