Dissociating explicit timing from temporal expectation with fMRI.

Explicit timing is engaged whenever subjects make a deliberate estimate of discrete duration in order to compare it with a previously memorised standard. Conversely, implicit timing is engaged, even without a specific instruction to time, whenever sensorimotor information is temporally structured and can be used to predict the duration of future events. Both emergent timing (motor) and temporal expectation (perceptual) are forms of implicit timing. Recent fMRI studies demonstrate discrete neural substrates for explicit and implicit timing. Specifically, basal ganglia are activated almost invariably by explicit timing, with co-activation of prefrontal, premotor and cerebellar areas being more context-dependent. Conversely, implicit perceptual timing (or "temporal expectation") recruits cortical action circuits, comprising inferior parietal and premotor areas, highlighting its role in the optimisation of prospective behaviour.

The hazards of time.

Temporal expectations are continuously formed and updated, and interact with expectations about other relevant attributes of events, in order to optimise our interaction with unfolding sensory stimulation. In this paper, we will highlight some evidence revealing the pervasive effects of temporal expectations in modulating perception and action, and reflect on the current state of understanding about their underlying neural systems and mechanisms.