Motor adaptation affects perception of time and numerosity

Abstract

We investigated the effect of motor adaptation on the perception of event duration and numerosity. Participants were asked to tap in mid-air with their dominant hand, either slowly (around 1 Hz), or as fast as possible (5–6 Hz). After 6 seconds of motor adaptation, a test stimulus (high-contrast 1 c/deg grating, drifting at 10 Hz for 300–1000 ms) was presented to the spatial region where the participant had tapped, followed by a similar grating of fixed duration (600 ms) in the opposite visual field. Subjects judged the relative duration of the two stimuli in two-alternative forced-choice, leading to psychometric functions that estimated the apparent duration of the test. Fast tapping decreased the apparent duration of the test, slow tapping increased it, both by about 20%. The effect of hand tapping was spatially specific, confined to a region within 10° of the tapping hand (irrespective of where the hand was positioned), showing that the effect is perceptual rather than cognitive. Similar experiments were performed for estimation of stimulus numerosity, both for random spatial arrays and for temporal sequences of flashes. Fast tapping decreased numerosity of both spatial and temporal sequences, and slow tapping increased it, again by about 20% in each direction. And again, the adaptation effects were confined to a region of 10° around the tapping hand. Tapping had no effect on more basic perceptual aspects such as apparent speed, suggesting that it operates at relatively high levels of analysis, probably in parietal cortex. Finally, we showed that making an abrupt arm movement after the motor adaptation completely annuls the effect of adaptation, resetting the system. Our results reinforce studies suggesting that visual time perception is closely linked with action, and suggest the existence of multiple local visuo-motor clocks.

Acknowledgement: ERC grant ESCPLANE