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Position-based motion perception for color and texture stimuli: Effects of contrast and speed.

Measured motion amplitude visual thresholds of computer- displayed oscillating gratings over a range of temporal frequencies. A total of 4 Ss participated in the set of 4 experiments. Exp 1 tested detection of equiluminant red-green gratings with a mechanism sensitive to velocity or position. Exp 2 used methods identical to Exp 1, with much higher color contrasts. Exp 3 used methods identical to Exp 2, excepting the use of higher contrasts of texture-defined stimuli. Exp 4 used patterns oscillating about an imaginary point circling the screen. Results show that the motion of low-contrast equiluminant red-green gratings is detected with position tracking. As contrast or speed increases, these results change: high contrast or high-speed equiluminant color or texture-based motion is detected by velocity- sensitive mechanisms. It is concluded that both position tracking and texture-based systems are available, but their relative efficiency changes as a function of contrast and speed. A position- tracking process is more sensitive at low contrasts and low speeds whereas a motion-energy system is more sensitive at high contrasts and high speeds. (PsycINFO Database Record (c) 2007 APA, all rights reserved)



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