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William Curran, Christopher Benton; The many directions of time. Journal of Vision 2011;11(11):1219. doi: 10.1167/11.11.1219.
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© ARVO (1962-2015); The Authors (2016-present)
Recent research has uncovered independent subsecond visual timing mechanisms, each monitoring a distinct region of visual space. We reveal that, rather than a one-to-one mapping of spatial location and timing mechanism, each region of visual space is assigned multiple, direction-contingent neural timing mechanisms. In Experiment 1, observers adapted to a peripheral, translating random dot kinematogram. Following adaptation, perceived duration was measured for a 600 ms test pattern in the same retinal location as the adaptor. The test pattern moved in either the same or opposite direction as the adaptor. Duration compression of the test pattern was observed in the former, but not the latter, condition; suggesting that multiple, neural timing mechanisms monitor each region of visual space. Furthermore, their direction-contingent nature points to these mechanisms being cortical in origin. Experiment 2 investigated whether these timing mechanisms occur at the global motion processing level. Following adaptation to a translating plaid pattern, which is known to selectively activate neurons in cortical area MT+, observers judged the duration of a random dot pattern moving in the same location and direction as the plaid. The resulting duration compression provides compelling evidence that the underlying neural timing mechanisms occur at the global motion processing level. Our results are consistent with a recent model of time perception (Periyadath & Eagleman, 2007), in which subjective duration of a stimulus is influenced by the amount of neural activity involved in representing the stimulus. Viewed from this perspective, the observed duration compression of test stimuli moving in the same direction as the adapting stimulus is driven by the reduced responsiveness of motion-sensitive neurons tuned to the adapting direction. The lack of duration compression for stimuli moving in the opposite direction is consistent with neurons sensitive to this direction maintaining their responsiveness in the face of the adaptation process.
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