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A paradox: Apparent onset locations for moving stimuli are more extrapolated following illusory reductions in speed.

26.403, Saturday, 17-May, 2:45 pm - 6:45 pm, Banyan Breezeway
Session: Motion Perception: Depth, higher order, illusions

Paul Miller1, Derek Arnold1; 1Perception Lab, School of Psychology, The University of Queensland

Humans make reliable errors when judging the instantaneous position of moving objects. In the Fröhlich effect, for example, the apparent onset location of a moving object seems advanced along its trajectory relative to static objects. We have found that this effect is malleable - exaggerated for tests following adaptation to motion in the same direction. We used arrays of rotating discs as an adaptor, and a single rotating disc in combination with static markers as a test. Neither opposite directional adaptation nor adaptation to slower movement had any impact. These data are counter-intuitive, as adaptation to fast motion reduced apparent test speeds, but exaggerated illusory displacements. Our data are consistent with apparent onset location being given by weighted positional estimates derived from multiple mechanisms with different integration times. We suggest that these estimates are re-weighted following adaptation to motion, increasing the relative contribution of mechanisms with more protracted integration times. This could be functionally adaptive, enhancing velocity judgments via increased temporal smoothing in dynamic conditions.

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