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Inci Ayhan, Aurelio Bruno, Alan Johnston; Adaptation induced temporal compression is highly space specific. Journal of Vision 2008;8(6):480. doi: https://doi.org/10.1167/8.6.480.
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Local adaptation to 20 Hz oscillatory motion or flicker reduces the apparent duration of a 10 Hz dynamic test stimulus, while 5 Hz adaptation has very little influence on apparent duration (Johnston, Arnold & Nishida, 2006, Current Biology, 16(5):472–9). Recently it has been suggested that the duration aftereffect can be attributed to a reduction in apparent speed, rather than a direct effect on neural timing mechanisms (Burr, Tozzi & Morrone, 2007, Nature Neuroscience, 10(4): 423–5). In our present study, we eliminated the influence of temporal frequency adaptation on speed judgements. First we varied the duty cycle of interleaved 5 and 20 Hz adaptation to find, for each subject, the critical ratio at which no change occurred in the perceived speed of a 10 Hz test pattern. We then used those ratios in a second experiment investigating the spatial specificity of temporal adaptation. In this experiment, the adaptor and the standard (10 Hz, 600 ms) always appeared on the right hand side of the fixation point while the comparison (300–1200 ms) always appeared directly on the left of fixation. The standard could appear at the same position, half overlapping (2.5 deg) or completely (5 deg) above and below the adaptation location. We compared the effects of adaptation against a control condition in which subjects made temporal judgements between comparison and standard drifting gratings in the absence of adaptation. In this case trials for the various positions of the standard were blocked. We found that the duration compression relative to the baseline conditions was highly spatially localised, appearing only in the overlapping condition. These results show that temporal duration compression occurs in the absence of changes in temporal frequency or speed and is highly specific to the location of the adaptor.
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