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Maryam Vaziri Pashkam, Patrick Cavanagh; Saccades to moving targets are not influenced by the speed overestimation at low luminance. Journal of Vision 2011;11(11):497. doi: 10.1167/11.11.497.
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© ARVO (1962-2015); The Authors (2016-present)
Previous studies showed that moving objects appear faster at low luminance (Hammett et al., 2007, Vaziri Pashkam & Cavanagh, 2008) as a result of the longer motion trace (Vaziri Pashkam & Cavanagh, 2008). Here we examine whether this faster perceived motion affects motor responses to the moving objects. We investigated saccadic eye movements to linearly translating random dot patterns. On each trial subjects were asked to compare the speed of a “target” random dot patterns to that of a “match” random dot pattern and make a saccade to the stimulus that they perceive to move faster. Stimuli were removed as soon as the subject initiated a saccade. The speed of the “target” and “match” were systematically varied to obtain the psychometric function of the subjects in the speed judgment task. In half of the experimental blocks both target and match were presented at high luminance. In the other half, the luminance of the match was reduced by covering half of the screen with 2.4 log unit neutral density filters. Subjects' saccade choices showed that they judged the low luminance stimuli to move faster than the high luminance one. However, the landing position of the saccades remained similar at high and low luminance: subjects did not overshoot the low-luminance target as might be expected from the increase in the perceived speed. We suggest that although motion blur contributes to perceived speed, it does not contribute to the speed information that influences motor reaction to moving targets. These results demonstrate a dissociation between perception and action in response to the speed of moving objects.
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