Independent coding of movement duration in a repetitive non-visually guided movement

Temporal information is an embedded feature of our sensory and motor experiences. How is temporal information encoded in the brain? In the two-stage theory of timing, an explicit representation of timing is responsible for the movement initiation while movement duration is coded implicitly. We investigated the correlation of movement duration and amplitude in a repetitive one-dimensional non-visually guided movement to find out if temporal information could be coded independently from movement. Subjects were asked to learn the distance between two points by moving their hands repeatedly along the distance between two sticks, while they could not see their hands and hand path. After a training phase, a delay of either 2 or 20 s was imposed and the subjects were asked to reproduce the learned distance. There was no correlation between distance difference and time difference in either delay condition. In the 20 s delay experiment, in comparison to the 2 s delay experiment, there was a significant increase in distance reproduction error. However, there was no significant change in time differences in either of the experiments. In addition, the time difference between the training and test trials was independent from the direction of the distance difference (i.e., overshot, undershot, or accurate). In conclusion, time may be coded as an independent measure after the delay period, so it should be a kind of explicitly coded information.