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Eriko Miyahara-Self, Catherine Tran, Naul Paz, Ashley Watson; The Role of S-Cone Signals in the Color-Motion Asynchrony. Journal of Vision 2010;10(7):436. doi: 10.1167/10.7.436.
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Background. In order to perceive simultaneous changes in color (e.g., from red to green) and motion direction (e.g., from upward to downward), the change in the motion direction needs to precede the color change by approximately 80 ms. This indicates color-motion asynchrony. This phenomenon has been investigated only with red and green stimuli that represent the L- and M-cone activity. The purpose of this study was to examine the asynchrony with stimuli that vary along the S/(L+M) axis as well as those that vary along the L/(L+M) axis. Because S-cone signals are processed more slowly than L- and M- cone signals, decreased asynchrony was expected with stimuli that vary along the S/(L+M) axis. Methods. Stimulus was 200 random equiluminant dots in a circular field of 8° in diameter. The direction of the motion of the dots was initially upward (or downward) and changed to downward (or upward) after 300 ms of the stimulus onset. The color of the dots changed once, either along the L/(L+M) or the S/(L+M) axis and the second color lasted for 300 ms. The relative timing of motion direction change and color change was varied from -100 to 250 ms in increments of 50 ms. The observer's task was to judge the predominant direction of motion of the second-color dots. The magnitude of color-motion asynchrony was assessed by the method of constant stimuli from four observers. Results. Surprisingly, the results showed that both stimuli that varied along the L/(L+M) axis and those that varied along the S/(L+M) axis produced perceptual asynchrony of about 90 ms. Conclusion. The equal magnitude of the color-motion asynchrony along the L/(L+M) and the S/(L+M) axes indicates that the color-motion asynchrony takes place in higher cortical areas beyond the integration of cone signals. This further supports the differential processing time model.
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