Mechanisms of Timing Across Tasks and Temporal Intervals.

Abstract

This dissertation investigates whether the information-processing instantiation of scalar expectancy theory (SET) is responsible for timing durations that span both the milliseconds and seconds ranges across perceptual and motor timing tasks. A common-timer view predicts that variability increases proportionally with increasing duration in a similar fashion across tasks. We use the coefficient of variation as an estimate of temporal sensitivity, and we perform Weber slope analysis to compare estimates of duration-dependent variance across durations and tasks. Other dependent variables included measures of temporal accuracy and response latency. Experiment 1 investigated whether a common mechanism can account for performance across a range of durations within a temporal reproduction task. The results were inconsistent with a single scalar timer across durations. Experiment 2 involved using endpoint pairs to reduce anchoring effects, a larger number of stimulus durations, and the addition of a similarly structured task that emphasized perception. Temporal reproduction and discrimination tasks were run in different subject groups, and again, the data challenge a single scalar timer within reproduction and point to separate timers for the two tasks. The third experiment examined the similarly structured temporal reproduction and discrimination tasks in a within-subjects design, eliminating the procedural differences between the tasks present in Experiment 2, and allowing for analysis of individual differences. The data again revealed nonlinear timing in the two tasks as well as evidence for task-specific clocks. Overall, these data argue against the possibility of a single scalar timer across durations in motor and perceptual timing and suggest a reformulation of the processes responsible for timing in these task conditions.