Effects of temporal uncertainty on watchkeeping performance

Abstract

Two experiments were conducted to assess the relative effects of signal density and regularity on watchkeeping performance. In Experiment I, three levels of density (6,24, and 91i signals/hr.) were combined factorially with three levels of variability (coefficients of variation of 0.01, 0.10, and 1.00), and 10 Ss were assigned at random to each of the nine conditions. In Experiment II, five leveIs of density (6, 12, 24, 48, and 96 signals/hr.) The uncertainty of the critical signal in a watchkeeping task can be expected to affect performance (cr., Alluisi, 1966, pp. 206-208). Indeed, the kind and degree of uncertainty define, at least in part, the difficulty of the watchkeeping task.In one of the earliest of watchkeeping studies, Mackworth (1950, pp. 53-63) reported that the deterioration in correct signal detections which typically occurred in his synthetic radar task could be delayed by increasing the brightness of the critical signals. This suggests that watchkeeping performance is a decreasing function of stimulus uncertainty (uncertainty concerning the nature of the critical signal). That is to say. as the signal-tonoise ratio of the critical signal is increased, performance efficiency also can be expected to increase. Although there have been few, if any, functional studies of stimulus uncertainty, it has been well established that this kind of uncertainty is likely to have some effect on watchkeeping performance (e.g., Adams, 1956;Bartlett et al , 1955;Jenkins, 1953Jenkins, , 1958.Spatial uncertainty(uncertainty concerning where the signal will appear) has been found to affect performance in visual watchkeeping tasks. Mackworth (1950, pp, 58-59), again using his synthetic radar task, found a progressive decline in the incidence of missed signals with rising spatial expectancy, or decreasing spatial uncertainty, and essentially similar results have been reported by other investigators (Deese & Ormond. 1953;Bartlett et al, 1955; Nicely & Miller,1957; Adams & Boulter, 1964).The third major source of uncertainty has also been studied; this is temporal uncertainty, or uncertainty concerning when a critical signal will occur. Both Ditchburn (1943) and Mackworth (1950) report that changes in the temporal intervals between signals produced associated changes in the proportions of signals missed. It appears from the results of later studies that changes either in signal frequency or in signal regularity may affect performance efficiency in watchkeeping tasks (e.g., Baker, 1959a, b;Bartlett et al , 1955;Broadbent, 1958;Deese, 1955;Deese & Ormond, 1953;Jenkins, 1958;Smith, 1961). These findings suggest that a psychophysical approach could be taken in studying watchkeeping performance, provided, of course, that the physical aspects of the uncertainty of the critical signal can be quantified and controlled. Such an approach has been taken in the present study in an attempt to determine the psychophysical relations between watchkeeping performance on the one hand, and the temporal uncertainty of the critical signa...

Variations in watch keeping performance as a function of the rate and duration of visual signals

“…Ten Ss were assigned at random to each level of signal rate; the order of appearance of signal duration was varied at random for each S across the five sessions in which he served. The statistical distributions of intersignal intervals for all levels of signal rate approximated the right-hand half of a normal distribution and were identical to those used previously (Smith et al, 1966). During each session, half of the signals appeared on each of the two display lights, but otherwise, the order of appearance of signals of the two different types was a random variable.…”

“…Smith et al, 1966) is complicated, and a valid psychophysics of watchkeeping will require additional considerations of the signal characteristics as well as the matrix of events in which they are embedded. and the average probability of a signal detection, given that both a signal and an observing response occur.…”

“…Where detection probability and signal rate have been found to be related, transient signalsof 0.5-sec duration or less have been used (Bowen, 1956;Deese & Ormond, 1953;Jenkins, 1958;Kappauf & Powe, 1959;Nicely & Miller, 1957). Also, where RT and signal rate have been found to be related, essentially unlimited stimulus durations have been employed (Smith et al, 1966). The conclusion must be reached that the interactions of such task and signal parameters have important effects on watchkeeping performances.…”

“…This study was designed to assess the relative effects on watchkeeping performance of five signal durations (0.5, 1.0, 2.0, 4.0, and 8.0sec) The duration and rate of critical signals are stimulus parameters that have been related to watchkeeping performances. In general, efficiency increases as rate is increased (Buck, 1966;Frankmann & Adams, 1962;Jerison & Pickett, 1963), and decreases as the temporal uncertainty of signals is increased (Smith et al, 1966). Watchkeeping efficiency also increases as the duration of the signal is increased (Adams, 1956;Baker, 1963;Fraser, 1957), over the small range of durations employed (cf.…”

Vigilance: A Review of the Literature and Applications to Sentry Duty

“…Critical signal density can also influence the speed with which signals are detected. Response time increases as a linear function of temporal uncertainty (Singh, Tiwari, & Singh, 2007;Smith, Warm, & Alluisi, 1966). Furthermore, the effects of signal probability can persist long after the conditions in which they were initially encountered.…”