PERFORMANCE AND PHYSIOLOGICAL AROUSAL DURING TWO VIGILANCE TASKS VARYING IN SIGNAL PRESENTATION RATE

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Summary.--The purpose of this study was to compare vigilance performance and level of arousal of two groups of Ss differing in the signal presentation rate they received. It was hypothesized that a gcoup receiving relatively infrequent signals would be over-aroused and would perform at a lower level primarily because they would be responding to irrelevant stimuli. Basal skin resistance and muscle potentials indicated that, as hypothesized, the Infrequent Ss were more hiahlv aroused than the Freauent Ss. Performance data indicated that -. the Infrequent group made a smaller percentage of correct detections and a much greater number of false alarms than the Frequent group. The specific question asked in this study was whether Ss who perform poorly on a vigilance task in which they receive infrequent signals are and falling asleep or overly aroused and responding to irrelevant stimuli. Several Es (Deese & Ormond, 1953; Jenkins, 1958; Kappauf & Powe, - 1959) have demonstrated that for varioi~s vigilance tasks, the more frequent the appearance of a signal, within limits, the less pronounced the deterioration of performance during the length of the watch. More recent investigators (Broadbent, 1963; Myers, Smith, & Murphy, 1963) have pointed out the importance of level of arousal in determining vigilance performance. Level of arousal is used here to denote the continuum of physiological activation of Ss (Hebb, 1955; Duffy, 1957; Malrno, 1959). Eason, Beardshall, and Jaffee ( 1965) obtained physiological measures of level of arousal of Ss experiencing two different rates of signal presentation. These Es hypothesized that the group receiving infrequent signals would perform at a lower level and show a lower level of arousal, i.e., a bored hypothesis; however, neither performance nor level of arousal indicated a significant difference between groups. Stern ( 1964a), in an earlier study in which various physiological indicants of arousal were obtained during a vigilance- type task, concluded that arousal level is determined by the interaction between task demands and sensory input. In that study, sensory input was acnlally held constant and task demands varied. In the present study, task demands were held constant, S had to report any movements of a small light, and sensory input varied, one. group received twice as many movements of the light as the other. It was hypothesized that the group receiving less frequent signals would be overly aroused and perform at a lower . level since they would be responding to irrelevant stimuli.