Measures of variations in performance during a sustained attention task.

In this study the authors developed and explored measures of short-term variations in accuracy on a test of sustained attention, a departure from traditional measures of average performance over long periods. The study participants were normal young adults, actively engaged in a continuous performance test (CPT). Both correct (hits) and incorrect (misses) responses to CPT targets appeared to aggregate in runs (2 or more consecutive hits or misses). Results of a Monte-Carlo procedure indicated that these runs were longer and fewer than would occur if hits and misses were randomly distributed. Average accuracy decreased between the first and second 5-min quarter of the test, then remained level. The length of hit runs followed the same pattern. However, other aspects of performance continued to change. The amount of time participants spent in miss runs began to increase significantly in the third quarter, and the frequency of miss runs did not increase until the fourth quarter. Explanations of these findings based upon changes in perceptual sensitivity or upon phasic increases in arousal caused by hits were rejected by further analysis. There was evidence that the length of miss runs was limited by a target-expectancy effect created by the specific parameters of our CPT. The authors conclude that measures of variations in performance reveal aspects of vigilance that are not tapped by traditional measures, and that factors that initiate, sustain and terminate both hit and miss runs are important targets of future research. Additional research is needed to determine whether or not the particular measures developed in this study may contribute to the understanding of attention problems in clinical populations.