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Laura Ortega, Emmanuel Guzman-Martinez, Marcia Grabowecky, Satoru Suzuki; Orientation-specific flicker adaptation dilates static time. Journal of Vision 2010;10(7):1415. doi: 10.1167/10.7.1415.
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Adapting to a flickering stimulus makes a subsequently presented static stimulus (in the order of 500-1000 ms) appear longer. This flicker-based time-dilation aftereffect has been thought to be mediated by central mechanisms such as increased arousal and attention. We investigated a potential role of low-level visual adaptation in this aftereffect. If flicker adaptation of low-level visual neurons contributes to subsequent temporal dilation, the aftereffect should be orientation specific, stronger when the orientations of the adaptor and test stimuli are the same than when they are different. The arousal hypothesis predicts no orientation specificity, the attention hypothesis predicts the opposite effect because attention capture by orientation change should make the different-orientation test stimulus appear longer, and contrast adaptation also predicts the opposite effect because the less visible same-orientation test stimulus should appear shorter. We used vertical and horizontal Gabors (4.17° radius, 4.32 cycles/deg) as the adaptor (flickered at 5 Hz or static; lasting 5000 ms) and test (static; lasting from 200 to 800 ms) stimuli. The perceived duration of the test stimulus was measured using a 2AFC temporal bisection task (shorter PSEs indicating temporal dilation). Overall, the test stimulus appeared longer (by 67 ms) when preceded by a flickered adaptor compared to a static adaptor, replicating the previous results. Crucially, the test stimulus appeared even longer (by 31 ms) when the flickered adaptor and the test Gabor had the same orientation than when they were orthogonal. These results suggest that flicker-based adaptation of orientation-tuned visual neurons contributes to temporal dilation over and above any effects of arousal, attention capture, and/or contrast adaptation. This orientation-specific time-dilation aftereffect is distinct from the recently reported location-specific but orientation-independent time shrinkage aftereffect (from rapidly flickering adaptor to flickering test). Time perception thus depends on the adaptive states of low-level visual processes in multiple ways.
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