Interaction of signal discriminability and task type in vigilance decrement.

Abstract

The results of recent studies suggest that perceptual sensitivity may decline over time in highevent-rate vigilance tasks either (1) when signals require successive, rather than simultaneous, discrimination or (2) when signals are difficult to discriminate from nonsignals. The joint effects of these two factors were examined in the present study. Two groups of subjects performed simultaneous- and successive-discrimination vigilance tasks requiring the discrimination of differences in line lengths at each of three levels of signal discriminabilitylow, moderate, and high. Both tasks lasted 30 min and had a high nonsignal-event rate. Perceptual sensitivity was assessed, using both parametric and nonparametric indices. For moderately or highly discriminable signals, sensitivity declined over time for the successive-discrimination task but not for the simultaneous-discrimination task. For low-discriminability signals, however, a sensitivity decrement was obtained for both tasks. These findings point to the role of the cumulative demand on attentional capacity in determining sensitivity decrement. The results are discussed in terms of attention allocation processes in high-event-rate vigilance tasks.