Systematic variation in performance of an interceptive action with changes in the temporal constraints.

People are highly skilled at intercepting moving objects and are capable of remarkably accurate timing. The timing accuracy required depends upon the period of time for which contact with a moving target is possible--the "time window" for successful interception. Studies of performance in an experimental interception task that allows this time window to be manipulated suggest that people change aspects of their performance (movement time, MT, and movement speed) in response to changes in the time window. However, this research did not establish whether the observed changes in performance were the results of a response to the time window per se or of independent responses to the quantities defining the time window (the size and speed of a moving target). Experiment 1 was designed to resolve this issue. The speed and size of the target were both varied, resulting in variations in the time window; MT was the primary dependent measure. Predictions of the hypothesis that people respond directly to changes in the time window were verified. Predictions of the alternative hypothesis that responses to changes in target speed and size are independent of one another were not supported. Experiment 2 examined how the type of performance change observed in Experiment 1 was affected by changing the time available for executing the interception. The time available and the target speed were varied, and MT was again the primary dependent measure. MT was smaller when there was less time available, and the effect of target speed (and hence the time window) on MT was also smaller, becoming undetectable at the shortest available time (0.4 s). The results of the two experiments are interpreted as providing information about the "rule" used to preprogramme movement parameters in anticipatory interceptive actions.