How does temporal blurring alter movement timing?

Abstract

Subjective uncertainty arises because the estimation of the timing of an event into the future is error prone. This impact of stimulus-bound uncertainty on movement preparation has often been investigated using reaction time tasks where a warning stimulus (WS) predicts the occurrence of a 'go' signal. The timing of the 'go' signal can be chosen from a particular probability distribution with a given variance or uncertainty. It has been repeatedly shown that reaction times covary with the shape of the used 'go' signal distribution. This is interpreted as evidence for temporal preparation. Moreover, the variance of the response time should always increase with the duration of the delay between the WS and the 'go' signal. This increasing variance has been interpreted as a consequence of the temporal 'blurring' of future events (scalar expectancy).The present paper tested the validity of the temporal 'blurring' hypothesis in humans with a simple oculomotor reaction time task where subjective and stimulus-bound uncertainties were increased. Subjective uncertainty about the timing of a 'go' signal was increased by lengthening the delay between the WS and the 'go' signal. Objective uncertainty was altered by increasing the variance of 'go' signal timing. Contrary to temporal blurring hypotheses, the study has shown that increasing the delay between events did not significantly increase movement timing variability. These results suggest that temporal blurring could not be a property of movement timing in an implicit timing context.Significance StatementIt is often assumed that the estimation of the timing of a distant future event is more error prone (or variable) than the estimation of a closer one. This phenomenon is referred to as temporal 'blurring'. Metaphorically, this could be compared in the spatial domain with the blurring of a visual stimulus when perceived at an increasing distance. Surprisingly, in the current oculomotor implicit timing task, movement variability actually decreased with the increasing temporal delay between a warning and an imperative 'go' signal. Therefore, temporal blurring is not a general property but depends on the precise context of timing behaviour.