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Michael J. Pesavento, John Schlag; Perceived sensorimotor simultaneity is learned. Journal of Vision 2004;4(8):287. doi: 10.1167/4.8.287.
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Synchronizing a tap or key press with a predictable event like a flash or a click depends on direct movement feedback (somesthetic, auditory, visual, or any combination). However, this feedback is not sufficient to explain the exact, usually small (<50 ms), value of the remaining asynchrony. This probably depends on past experience, taking in account the anticipated timing of the movement outcome. Here we verify that the perceived synchrony in a coincidence-anticipation task can be modified by the transfer of adaptation produced in a different task (pacing). In the coincidence-anticipation task, a vertical bar horizontally moving at constant speed crossed a vertical line in the middle of a monitor screen. Subjects (n=19) were instructed to press a key exactly when the bar crossed the line. They had no feedback on their performance. This test task was run before and after an adapting pacing task in which a red square was flashed every second at the center of the screen. Subjects were instructed to press a key exactly in synchrony with the flash. Outcome feedback was provided by flashing a blue square below the red square. There were 2 types of sessions: one in which the outcome feedback was immediate, the other (adapting) in which this feedback was progressively delayed (up to 100 ms). Whereas subjects' asynchrony was unchanged in the first case, it was significantly increased in the pacing task with delay. This increase transferred to the subsequent coincidence-anticipation task and was significant, even though subjects were not aware that their sensorimotor asynchrony had been lengthened (sometimes doubled). We conclude that perception of simultaneity in a sensorimotor task is learned. If this perception is caused by coincidence of signals in the brain, the timing of these signals depends on something — acquired by experience — besides physiological latencies. This observation may help in guiding the search of correlates of simultaneity detectors in the brain.
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