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Perceived velocity of moving chromatic gratings.

Evaluated the perceived velocity of drifting chromatic gratings at a range of luminance contrasts around the equiluminance setting. The 3 authors and 1 naive observer participated in a series of experiments. Equiluminous red-green sine-wave grating were drifted at a uniform rate in the bottom half of a 10 deg field. In the top half of the display was a sinusoidal-luminance grating of the same spatial frequency and 95% contrast that drifted in the opposite direction. Ss, while fixating a point in the display center, adjusted the speed of this upper comparison grating so that it appeared to match the velocity of the chromatic grating below. At low spatial frequencies, equiluminous gratings were appreciably slowed and sometimes stopped even though the individual bars of the grating could be easily resolved. The amount of slowing was proportionally greatest for gratings with slow drift rates. Blue-yellow sine-wave gratings showed similar effects. When luminance contrast was held constant, increasing chrominance modulation caused further decreases in apparent velocity, ruling out the possibility that the slowing was simply due to decreased luminance contrast. Perceived velocity appears to be a weighted average of luminance and chrominance velocity information. (PsycINFO Database Record (c) 2007 APA, all rights reserved)



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