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Saumil S. Patel, Susana T.L. Chung, Harold E. Bedell, Haluk Ogmen; Color and motion: which is the tortoise and which is the hare?. Journal of Vision 2002;2(7):143. doi: 10.1167/2.7.143.
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© ARVO (1962-2015); The Authors (2016-present)
Recent psychophysical studies have been interpreted to indicate the perception of motion temporally lags the perception of color. We sought to evaluate the generality of this interpretation, using targets with a range of motion directions and velocities, and two psychophysical tasks.
Observers viewed a 18 sq.deg field of colored dots that moved at a constant speed (15–60 deg/s), and periodically changed their color (red/green) and direction of motion (up/down or up/left). In one experiment, the observers' task was to judge the predominant color of the dots during upward motion. In a second experiment, the observers judged whether the change in dot color occurred before or after the change in the direction of motion.
When the direction of dot motion reverses from up to down, our results confirm previous reports that one color is perceived to be predominant for each direction of motion if the phase of dot-motion change is advanced approximately 150 ms with respect to the change in dot color. However, when the direction of dot motion changes from up to left, the relative phase of dot-motion change shifts systematically from a phase advance (ca. 60 ms) to a phase delay (ca. 20 ms) as the speed of motion increases. In the second experiment, dot color and dot motion are perceived to change simultaneously when the phase of dot-motion change is delayed slightly with respect to the change in dot color, regardless of the angular direction change or dot speed.
Our results can be explained by considering how the stimulus and experimental task interface with various stages of color and motion processing. A task that requires the averaging of color information for motion in a specific direction involves neural processing that is unnecessary if just a change in motion direction or color has to be detected. If the moving stimulus reverses its direction, we suggest that a motion-opponency stage is engaged, which substantially slows the dynamics of motion processing.
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