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Farshad Moradi, Shinsuke Shimojo; Surface segregation and the time-course of feature-binding. Journal of Vision 2004;4(8):498. doi: 10.1167/4.8.498.
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Color and motion are registered in distinct brain regions. Functional separation could impose a constraint on how fast these attributes are combined into a unified percept. We measured the temporal resolution of color-motion binding by presenting two alternating random dot patterns (red moving left vs. green moving right). Observers were asked to pair color and direction of motion. Pairing was impaired as the alternation rate increased from 1.4 Hz to 4.2 Hz, suggesting that perceptual-binding is a slow process that requires temporal integration, and that consecutive attributes interfere with each other. Performance recovered after adding either of the following surface transparency cues: 1) presenting red and green pattern concurrently, 2) superimposing irrelevant patterns (blue/gray, with vertical motion), 3) superimposing stationary patterns, or 4) increasing the alternation frequency to 8.5 Hz (which results in perceptual transparency). Transparency provides a segregation cue which prevents interference between surfaces, thus only features that belong to the same visual entity can be bound together. Next we examined if segregation precedes binding. Two stationary patterns (red, green) were superimposed. One pattern moved briefly (24 – 120 ms). Both patterns were temporarily turned gray during motion, and either returned to their original color or switched colors. Observers were asked to report the color of the moving dots. Interestingly, gray was reported in less than 10% of the trials. In 70% of the trials, observed reported the color that followed motion, regardless of the original color. Our findings imply that asynchrony in binding does not reflect different latencies, temporal references, or dynamics for color and motion. Instead, we argue that color is registered over a temporal window defined by perceptual (motion-based) segregation, which lags behind the physical onset of the motion.
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