The effects of time, rate of information presentation and physical threat stress were investigated through the use of on-line computer techniques to measure performance on three simultaneously occurring tasks. The three tasks consisted of complex discrimination, psychomotor coordination, and warning light monitoring. Thirty-six male naval aviation officer candidates were randomly assigned to 4 groups of 9 S s each. Stress was produced by the threat of a mild electric shock if the appropriate response was not made within 3 seconds after the occurrence of the warning light. No-stress groups also performed the same monitoring task but without the threat of shock. The presentation rate of the stimuli associated with the psychomotor coordination task was either varied or held constant as the three tasks were performed for 43.2 minutes. The variables of stress and presentation rate acted primarily to determine S's allocation of attention to the three tasks in the early part of the test session. With increased time on task, total performance improved, but the initial differences in the speed and accuracy measures of group performance diminished. These results were found to be consistent with the assumptions of capacity models of attention and also denote the importance of the duration of experimental test sessions as a procedural consideration.
