SIGNAL DETECTION AS A FUNCTION OF INTERSIGNAL INTERVAL DURATION
HUMAN FACTORS RESEARCH INC LOS ANGELES CA
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The probability of signal detection as a function of intersignal interval duration was determined from data obtained in 3 studies of vigilance performance. In one study, the distribution of intersignal intervals was positively skewed, there were many more brief intervals than long intervals. In other studies, the distributions of intervals were rectangular. The intersignal intervals were identified by 1 the amount of time since the previous signal was detected, 2 the amount of time since the previous signal occurred, and 3 the amount of time since the previous signal was missed. The results support an expectancy theory of vigilance, if theory is modified to state that expectancy and hence probability of detection is highest at the modal rather than the mean intersignal interval.