Abstract
The ability to predict upcoming events is important to compensate for relatively long sensory reaction delays. When stimuli are temporally regular, their prediction depends on an implicit representation of elapsed time. However, it is unclear whether the underlying timing mechanism is separable from a conscious, explicit perception of time, and whether it is shared by different motor effectors. To probe the temporal processing component of prediction, subjects performed an implicit timing task, where they used smooth pursuit eye movements to accurately track a fast-moving target after a constant-duration blank interval. The task was performed either in isolation, or concurrently with an explicit timing task, where a manual response was required at the instant of target motion onset. The onset of anticipatory pursuit eye movements was used to quantify the subject's implicit estimate of elapsed time. Onset times were delayed significantly in blocks with the concurrent manual task relative to the pursuit task in isolation. During the concurrent task there was also a correlation between the oculomotor and manual response latencies, and both modalities showed an influence of responses from preceding trials. In the framework of the Scalar Expectancy Theory (SET) model, the results are consistent with a centralized attentional gating mechanism that allocates clock resources between explicitly- and implicitly-timed tasks. Model simulations show that slow fluctuations of the attentional gate could account for the observed influence of previous trial responses.
Supported by an Action de Recherche Concertée from the Université catholique de Louvain.