Abstract
Signal frequency (1, 10, and 20 signals per hour) and signal flash rate (one signal every 2 and 1¼ sec.) were varied in two vigilance experiments using a “noisy” simulated radar display as the sensory input. The results indicated small changes in vigilance over the course of 1 hr. The data suggest that vigilance will decrease, stay level, or improve as a function of signal frequency and the inherent detectability of the critical signal. It is suggested that vigilance behavior is related to the extent to which S can comprehend (and hence predict) the temporal pattern of critical signals. It is concluded that not enough is known about the conditions which determine the occurrences of decrement in vigilance.

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