Effects of Task Type and Stimulus Heterogeneity on the Event Rate Function in Sustained Attention

The goals of the present experiment were (1) to determine the function relating rate of presentation of neutral background events to accuracy of signal detection in both a simultaneous (comparative judgment) and a successive (absolute judgment) vigilance task, and (2) to test differential predictions from Posner's pathway inhibition theory and Jerison's elicited observing-rate theory about the effects of heterogeneity in the shape of the neutral events. Data for simultaneous and successive tasks at four event rates (6, 12, 24, and 48 events/min) under both homogeneous and heterogeneous neutral-event conditions showed that the event-rate function (a decline in detections with increments in event rate) was steeper for the successive than for the simultaneous task. Consistent with Jerison's view but not with Posner's, stimulus heterogeneity did not moderate the effects of either time on watch or event rate.