Equivalent background speed in recovery from motion adaptation.
We measured, in the same observers, (1) the detectability, d, of a small rotational jump following adaptation to rotational motion and (2) the detectability of the same jump when superimposed on one of several background rotation speeds. Following 90 s of motion adaptation the detectability of the jump was impaired, and sensitivity slowly recovered over the course of 60 s. The detectability of the jump was also impaired by the background speed in a way consistent with a quadratic form of Weber's law. We propose that motion adaptation impairs the detectability of the small jump because it is as if an equivalent background speed has been superimposed on the display. We measured the equivalent background by finding the real background speed that produced the same d' at each instant in the recovery from motion adaptation. The equivalent background started at approximately one to two thirds the speed of the adapting motion, declined rapidly, rose to a small peak at 30 s, then disappeared by 60 s. Since the equivalent background speed corresponds to the speed of the motion aftereffect, we have measured the time course of the motion aftereffect with objective psychophysics.
Simpson
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Department of Psychology, University of Winnipeg, Manitoba, Canada. wsimpson@uwinnipeg.ca
Newman
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Aasland
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D000222:Adaptation, Physiological; D000360:Afterimage / Q000502:physiology; D006801:Humans; D008433:Mathematics; D009039:Motion Perception / Q000502:physiology*; D011601:Psychophysics; D012399:Rotation