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Laura Ortega, Emmanuel Guzman-Martinez, Marcia Grabowecky, Satoru Suzuki; The time-dilation aftereffect depends on orientation and eye of origin. Journal of Vision 2011;11(11):1226. doi: 10.1167/11.11.1226.
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Several seconds of adaptation to a flickered (5 Hz) stimulus makes a subsequently presented brief static stimulus appear longer in duration. What causes this time-dilation aftereffect? We investigated this question using a standard temporal-bisection task, where observers classify (in a 2AFC manner) whether the test stimulus, varying between 200 and 800 ms, is closer to the short or long reference duration remembered prior to experimental trials. A shorter PSE (i.e., a shorter physical duration perceived to be the bisection point of 500 ms) indicates a larger amount of perceptual time dilation. Using this technique, we previously showed that the flicker adaptation time-dilation aftereffect is significantly reduced by a 90° change in Gabor orientation between adaptation and test. However, high-level as well as low-level visual neurons are sensitive to a 90° orientation change, and observers were conscious of the orientation change. Our previous results thus are consistent with contributions from high-level visual processing and/or cognitive processing as well as with low-level processing. Our current experiments demonstrate that the time-dilation aftereffect is also significantly reduced by a much smaller 45° orientation change, suggesting the involvement of lower-level visual neurons (orientation-tuning bandwidths are approximately 25–40° in V1, 35–75° in V4, and 70° in IT). Furthermore, the time-dilation aftereffect is significantly reduced when the adaptor and test stimuli are presented to different eyes than when they are presented to the same eye. Because eye preferences are strong in V1 but diminish in high-level visual areas, the specificity for eye of origin corroborates the involvement of low-level visual neurons. Further, because people are generally unaware of the eye-of-origin information, cognitive processing is unlikely to have mediated this specificity. Taken together, our results suggest that flicker adaptation of low-level visual neurons contributes to expanding the perceived duration of a subsequently presented static stimulus.
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