The Elicited Observing Rate and Decision Processes in Vigilance

Abstract

Observers detected many more of a fixed number of signals when these were among stimuli presented at 5 per minute than when these were among stimuli presented at 30 or 60 per minute. The effect, which is associated with either the signal probability or the nonsignal stimulus density, is analyzed with conventional measures and with measures from the theory of signal detectability (TSD). The TSD measures were used to define several possible modes of observing, and the model of vigilance based on decisions about observing could then be related to decision processes in detection performance as considered by TSD. If a single measure of the probability of alert observing is required, the best one is the percentage of detections of the readily detectable signal of the vigilance task. However, the TSD analysis suggested various different “mixes” of modes of observing for the subgroups in this experiment, and these mixes could be specified with the the help of heuristic models relating performance measures to the probability of observing.