Working memory affects motor, but not perceptual timing

Whether different timing tasks utilize the same brain processes is still debated. To address this question, we investigated how working memory affects two different timing tasks: time reproduction and time discrimination. We found that delay intervals led to an overestimation in the reproduction task but did not introduce any bias in the perception of time in the discrimination task. Delay intervals affected the perception of time when subjects had to actively reproduce the perceived interval, but not when subjects were merely recalling the content of working memory. In subsequent Bayesian modeling, we showed that in the reproduction task, subjects updated their measurement of the stimulus on the current trial (likelihood) based on the delay interval, rather than changes in the motor system or updating priors based on the delay interval. Our findings suggest that the brain processes involved in time reproduction and discrimination are not completely overlapping, and that delay intervals in working memory tasks lead to changes in updating the likelihood. This robustness in prior and updates in likelihood provides both stability and sensitivity in the perception of time.