Motor commands induce time compression for tactile stimuli

The link between time perception and action has attracted special interest in recent years and it is progressively disclosing a multifaceted nature.A large set of temporal effects variously associated to the execution of actions has been documented (Haggard et al., 2002; Hagura et al., 2012; Tomassini et al., 2012; Yarrow et al., 2001), suggesting that perceived time may directly emerge from sensory-motor processes.Saccadic eye movements have been shown to cause not only compression of the visual space towards the saccadic target, but also a compression of time.Apparent event time is both shifted and compressed so that the temporal separation of two visual stimuli is strongly reduced and even their order of appearance sometimes reversed.The spatial and temporal distortions are thought to be interconnected phenomena that might be related to the problem of maintaining perceptual stability during eye movements (Burr & Morrone, 2012; Cicchini et al., 2013).Interestingly, evidence suggests that similar phenomena may occur around the time of hand movements, when brief tactile stimuli are systematically mislocalized in the direction of the movement.In this study we measured whether hand movements also cause an alteration of the perceived timing of the tactile signals.Participants compared the temporal separation between two pairs of tactile taps while moving their right hand in response to an auditory cue.The first pair of tactile taps was presented at variable times with respect to movement with a fixed onset asynchrony of 150 ms. 2 s after test presentation -when the hand was stationary-the second pair of taps was delivered with a variable temporal separation.Tactile stimuli could be delivered either to the right moving or left stationary hand.We found that when the tactile stimuli were presented on the motor effector, their perceived temporal separation was reduced.The compression of time began in stationary conditions, during the motor preparatory period, and persisted during movement.Critically, at the moments around action initiation, time compression was restricted to the motor effector.Duration was misjudged only when tactile stimuli were delivered to the hand that was about to move and not when delivered to the other, stationary hand.That time compression is effector-specific makes highly implausible any explanation based on high-level attentional modulations.Rather, it points to a specific mechanism based on a finely-tuned sensory-motor coupling.To understand better the nature and origin of the temporal distortion accompanying hand movements we tested also an isometric condition.Motor efference, with no associated spatial displacement of any body part, induced comparable compression of perceived time as actual movement.An intention-to-move signal, seems thus to be sufficient to mediate the observed perceptual effects.Our result corroborates recent evidence of a tight link between time perception and action and shows a selective and anticipatory movement-related distortion of time.The changes in apparent time that we observed for tactile stimuli at the moment of hand movements closely resemble the peri-saccadic distortions of visual time.As for vision, the mislocalizations of time and space of touch stimuli may be consequences of a mechanism attempting to achieve perceptual stability, suggesting that different sensorimotor systems may exploit similar strategies during the active exploration of the environment.