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Aurelio Bruno, Alan Johnston; Contrast gain changes affect the perceived duration of visual stimuli. Journal of Vision 2007;7(9):376. doi: 10.1167/7.9.376.
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Increasing stimulus contrast can shorten the temporal impulse response in the M cells of the macaque monkey, but not in P cells (Kaplan & Benardete, 2001, Prog Brain Res, 134:17–34). The shortening of the temporal impulse response function has been proposed as a possible cause of perceived duration distortions (Johnston, Arnold & Nishida, 2006, Current Biology, 16(5):472–9). We investigated the influence of luminance contrast context on the apparent duration of a visual stimulus. Subjects were presented with two test intervals (one of them with different durations across trials) containing a drifting grating of 50% contrast embedded in a variable contrast sequence of oscillating motion and they indicated which one contained the longer stimulus. In the first condition, in the initial and the final intervals the grating contrast was set to 90%, while in the intervening interval it was set to 10%. In a second condition, the first and last interval contrast was 10%, while the intervening one was 90%. The orientation of the gratings in the test intervals was orthogonal to those in the background intervals and we varied the temporal frequency of the stimuli in a range between 2 and 20 Hz. We found that the duration judgments obtained in the two conditions differ only when the stimuli oscillated at high-temporal frequencies. When the test interval was preceded by a high-contrast interval, we observed a shrinkage of its perceived duration, while when the preceding interval contrast was low, the test appeared to last longer. We also showed that the differences in the onset-offset perception of the stimuli in the two conditions cannot account for the observed effects. The specificity of this contrast effect on time perception to high-temporal frequencies and the greater sensitivity of magno cells to contrast adaptation suggest that the underlying mechanisms are in the magnocellular pathway.
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