Timing of Discrete Actions: Evidence for Perceptual Dominance in Human Performance

An experiment involving a street-crossing task is described. The subjects were required to release a pedestrian within a narrow window of opportunity to cross the road without being run over by vehicles. To test a number of hypotheses on whether timing of actions is driven by perceptual cues or some internal clocking mechanisms, the experiment involved conditions where the street-crossing task was either visible throughout trials or where the vehicles were removed, and coupled with a concurrent mental arithmetic loading task with either visually or auditorily presented stimuli The data support the hypothesis that when the stimuli remain visible, people predominantly rely on perceptual cues for timing discrete actions. Significant performance decrements were observed in the removal conditions Importance of the visual component in the task performance was supported by the larger performance decrement in the unmasked condition when the subjects' attention had to be divided between two sets of visual stimuli. When the primary task stimuli were removed, the clock counting seems to be the preferred strategy for the task under study.