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Kiyoshi Fujimoto, Takao Sato; Motion induction by biological motion. Journal of Vision 2002;2(7):337. doi: 10.1167/2.7.337.
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© ARVO (1962-2015); The Authors (2016-present)
We found a new visual illusion caused by biological motion, in which a background pattern appears to move oppositely to a human locomotion indicated by gait. To exemplify this phenomenon, we conducted two experiments presenting an ambiguous motion as a background of a point-lights walker stepping on a tread-mill. In experiment 1, observers judged motion direction of a counterphase grating with a 2-alternative forced choice method (left or right). In experiment 2, random dot kinematograms (RDK) with varying signal-noise ratios were used to evaluate sensitivity for coherent motion. Results indicated that the counterphase grating appeared to move in the direction opposite to that of walking in 75% of trials, significantly higher than chance level. As for RDK backgrounds, the psychometric function for coherent motion sensitivity was biased toward the direction opposite to walking. In addition, such tendencies disappeared when configurations of point-lights were scrambled, although total composition of 1st-order motions was unchanged. Since the earlier visual system is not likely to detect biological motion, these results indicate involvements of the higher visual system in the induction. The results also indicate that the output of such high level processes as those involved in biological motion effectively interact with low level motion output.
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