The effects of time stress and task difficulty on closed-loop tracking performance and physiological correlates

Abstract

An exploratory study was conducted to determine changes in human performance and physiological correlates in a time-limited situation involving pursuit tracking. The tracking task involved a cathode ray oscilloscope in closed-loop with a control stick. This area of research has been termed a study of "deadline behavior" and the psychological state occurring in deadline situations has been discussed as a state of "time-stress." "Time-stress" was hypothesized to occur more commonly in situations where the outcome is perceived as being uncertain than in situations where the outcome is perceived as being obvious based on the subject's previous performance. Twenty male college students performed nine pursuit tracking tasks which were combinations of three levels of time constraint and three levels of task difficulty. Levels of time constraint represented 100%, 60%, and 40% of the subject's own task time requirement at the end of training while working at the same task without a time limit. Subjects received a monetary reward for completing ten sub-tasks or target lock-ons before time on a clock displayed to the subject had expired. Levels of difficulty were introduced by three ''time constants" representing minimum durations of target superimposition required for lock-on. The physiological correlates which were recorded were autonomic changes in heart rate, respiration rate, and skin resistance levels. The principal findings were that several aspects of performance improved with increasing time constraint. Increasing task difficulty was associated with increased variability in the time between sub-task completions, reduced efficiency in acquiring targets, but also less integrated absolute error. Autonomic changes were found to be related to the treatment conditions. The heart rate data suggested a reduction in effort on those tasks which were failed badly and an increase in effort on tasks where the outcome was in doubt until the end. The experimental technique of basing experimental time limits upon the subject's time requirements during training was found to be successful in preventing differences in subject's skill from confounding difference due to the treatment conditions.