AbstractRecent evidence suggest that our experience of time is directly and intrinsically computed within the motor system. Accordingly, a variety of studies have demonstrated that concurrent movement impacts the estimate of temporal duration, such that perceived time is shifted towards the duration of movement. In order to investigate the role of the motor system, we tested human subjects (n=40) on a novel task combining reaching and time perception. In this task, subjects were required to move a robotic manipulandum to one of two physical locations to categorize a concurrently timed suprasecond auditory stimulus as “long” or “short”, relative to a running average criterion. Critically, subjects were divided into two groups: one in which movement during the interval was unrestricted and subjects could move freely to their choice, and one in which they were restrained from moving until the stimulus interval had elapsed. Our results revealed a higher degree of precision for subjects in the free-moving group. By further decomposing choice and response time data with a drift diffusion model of decision making, we identified the source of this change to a shift in the response threshold for free-moving subjects. Analysis of movement parameters revealed that eventual choice could be determined by movement parameters (e.g. trajectory, force) before the response was made, and even before the interval had elapsed, and that the variability of these movements was lower in the unrestrained group. A further experiment (n=14) verified that these findings were not due to proximity to the target, counting strategies, bias, or movement length. Our findings suggest that perceptual timing may be instantiated within the motor system as an ongoing readout of timing judgment and confidence.
Denumerable state continuous time Markov decision processes with unbounded cost and transition rates under average criterion