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William Curran, Christopher P. Benton, Julie M. Harris, Paul B. Hibbard, Lee Beattie; Local and global mechanisms mediate perceived duration of brief visual events. Journal of Vision 2014;14(10):1146. doi: https://doi.org/10.1167/14.10.1146.
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© ARVO (1962-2015); The Authors (2016-present)
Adapting to a spatially localized drifting dot stimulus results in the duration of a subsequent stimulus in the same location being underestimated. This duration compression effect is direction contingent (Curran & Benton, 2012), and likely driven by adaptation of cortical timing mechanisms. What is unclear is whether the adapted mechanisms are at the local or global motion processing level. Our experiments address this question. Experiment 1 measured perceived duration while manipulating the adaptors motion coherence (0-100%). The adaptor and test stimuli were centered 5 deg to one side of fixation, and the comparison was centered 5 deg to the opposite side. Following adaptation, observers judged whether the comparison stimulus had a longer or shorter duration than the 600ms test stimulus. Presentation order of test and comparison was randomised. Our results show a linear relationship between adaptor coherence and duration compression magnitude. Experiment 2 repeated the coherence experiment while keeping adaptor global speed fixed. The results reveal that, although duration compression persisted, motion coherence level did not influence duration compression magnitude. This suggests that the duration compression magnitude in experiment 1 was driven by adaptor speed, not adaptor coherence; although it is not clear whether the determining factor was the adaptors local or global speed. Experiment 3 used multiple-Gabor stimuli to investigate the role of local and global mechanisms. The global direction was identical for the adaptor and test stimuli; however in one condition the test pattern of Gabor orientations (hence directions) was identical to the adaptor, and in the second condition each adaptor Gabor element was replaced with its orthogonal orientation in the test stimulus. Duration compression was found for both conditions, demonstrating that global motion mechanisms are involved in sub-second event timing. However, compression magnitude was reduced in the orthogonal condition suggesting that local mechanisms also play a role.
Meeting abstract presented at VSS 2014
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