Workload Transition Implications for Individual and Team Performance (1993) / Chapter Skim
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6 Vigilance and Target Detection
6 Vigilance and Target Detection
Pages 139-170
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From page 139... ...
In this chapter we examine in detail the research on human performance in monitoring, vigilance, and target detection. HISTORICAL BACKGROUND World War II Vigilance or sustained attention refers to the ability of observers to maintain their focus of attention and to remain alert to stimuli for prolonged periods of time (Davies and Parasuraman, 1982; Warm, 1984a)
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From page 140... ...
It has been labeled the "decrement function" or the "vigilance decrement" and is the most ubiquitous finding in vigilance studies. Many investigations using a broad assortment of vigilance tasks indicate that the decline in performance is complete from 20 to 35 minutes after the initiation of the vigil and at least half of the final loss is completed within the first 15 minutes (Teichner, 1974~.
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From page 141... ...
All of this must be accomplished under extreme conditions of heat, noise, vibration, and danger. In order to provide some insight into factors that might affect the vigilant behavior of armor crews and ways to counter threats to their ability to remain alert, this chapter describes a variety of task and environmental factors that have been discovered to play an important role in the quality of vigilance performance.
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From page 142... ...
, the characteristics of the background of nonsignal events in which critical signals for detection are embedded (B) , and task complexity (C)
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From page 143... ...
The more frequently such signals occur within a fixed time period, the greater the a priori signal probability and the lower will be the subject's average uncertainty as to when critical signals will occur. The accuracy of signal detections varies directly as a function of signal density (Warm and Jerison, 1984~.
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From page 144... ...
The frequency of background events, or the background event rate, is a very important determinant of performance efficiency. Both the speed and the accuracy of signal detections vary inversely with event rate, and the vigilance decrement tends to be more pronounced in the context of a fast compared with a slow event rate (Jerison and Pickett, 1964; Lanzetta et al., 1987; Parasuraman, 1979; Parasuraman and Davies, 1976~.
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From page 145... ...
Taken together, findings such as these have led several investigators to conclude that background event rate is probably the prepotent psychophysical factor in vigilance performance (Parasuraman et al., 19871. For the most part, neutral events in vigilance experiments have been presented in temporally regular intervals, such as 1 event every 12 seconds at an event rate of 5 per minute or 1 event every 2 seconds at a faster rate of 30 per minute.
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From page 146... ...
In a carefully conducted experiment in which automatic processing was developed over several hundred trials, Fisk and Schneider found that the vigilance decrement was restricted to controlled processing tasks; automatic tasks were performed in a stable manner throughout the vigilance session. Evidently, proper training might be a key in aiding subjects to cope with demanding vigilance tasks.
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From page 147... ...
, perhaps because subjects develop more rational expectations of the actual signal probability in force with experience in the experiment (Davies and Parasuraman, 1982; Swets, 1977; Warm and Jerison, 1984; Williges, 1969~. True perceptual decrements seem to be restricted to extremely demanding situations with low levels of signal discriminability, which may be brought about by low signal-to-noise ratios, fast event rates, and memory demanding tasks (Parasuraman et al., 19873.
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From page 148... ...
Along these lines, the degrading effects of increments in event rate, event asynchrony, and the spatial uncertainty of signals have all been found to be more notable with successive than with simultaneous tasks (Josh) et al., 1985, Lanzetta et al., 1987; Scerbo et al., 1987a)
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From page 149... ...
Vigilance performance breaks down with perturbations in core temperature, remains unaffected when there is no variation in that temperature, and can be facilitated when subjects are established in a static hyperthermic state. Only a few studies have examined the effects of cold on vigilance performance.
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From page 150... ...
have reported that loud continuous noise degrades the speed and accuracy of signal detections in multidisplay monitoring tasks. The general effects of continuous noise on the quality of vigilant behavior can be summarized as follows: performance is degraded by loud noise (above 9OdB SPL)
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From page 151... ...
Several other studies have shown that, after one night of total sleep deprivation, the overall speed and accuracy of signal detections declined as did perceptual sensitivity, and that the vigilance decrement can be exacerbated. In air crews, vigilance tasks are found to be the first affected by fatigue.
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From page 152... ...
, and Wilkinson and his colleagues (Wilkinson, 1968; Wilkinson et al., 1966) have shown that reduced sleep regimens impaired vigilance performance in comparison to control sleep schedules.
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The task consisted of a simulated air traffic control radar system that displayed targets flying along specified routes at different speeds. Critical signals for detection consisted of departures from altitude as reflected in alphanumeric readouts on the radar screen.
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(1989) examined the effects of extratask demands and long hours of work on the performance of simultaneous and successive vigilance tasks in a simulated work environment.
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(1991) found that providing subjects with brief whiffs of air containing the scent of mugger or peppermint can enhance the probability of signal detections in vigilance compared with plain air control conditions.
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From page 156... ...
These investigators examined the effects of abrupt shifts in event rate in a low to high as well as in a high to low direction and found that such shifts had strong effects on monitoring efficiency. The frequency of signal detections for subjects shifted from a low to a high event rate was considerably poorer than that for control subjects maintained on the high event rate throughout the vigilance session.
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From page 157... ...
, Gluckman's (1990) findings also suggest that the effects of workload transitions on vigilance performance are complex-they seem to depend on the precise manner in which such changes are brought about.
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From page 158... ...
Throughout this chapter emphasis has been placed on the importance of resource utilization as a way of understanding vigilance performance. It is clear that successive tasks drain more processing capacity than simultaneous tasks.
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From page 159... ...
Moreover, except for one study involving signal density (Bergum and Lehr, 1962) , none of the available experiments has explored the influence of important psychophysical variables on the effectiveness of team monitoring.
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have also pointed out that training for automatic processing can make vigilance performance more resistant to the effects of environmental stress and increased mental workload, findings that add to the potential importance of a good training regimen and that fit well with Wilkinson's (1969) claim that familiarity with a task is a primary way to insulate performance against the effects of stress.
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1983 Stimulus Homogeneity and the Event Rate Function in Sustained Attention. Doctoral dissertation, University of Cincinnati, Cincinnati, Ohio.
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Warm, and W.N. Dember 1985 Effects of knowledge of results on performance in successive and simultaneous vigilance tasks: A signal detection analysis.
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Warm 1989 Effects of Event Rate on Subjective Workload in Vigilance Performance. Paper presented at the meeting of the Southern Society for Philosophy and Psychology, Chicago, Illinois.
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Johnson, R.F., and D.J. McMenemy 1989 Target detection, rifle marksmanship and mood during three hours of sentry duty.
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Warm 1977 The event rate context in vigilance: Relation to signal probability and expectancy. Bulletin of the Psychonomic Society 10(5)
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Moore, S.F., and S.J. Gross 1973 Influence of critical signal regularity, stimulus event matrix and cognitive style on vigilance performance.
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See, J.E. 1992 Effects of Transitions in Signal Salience on Vigilance Performance.
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Smith 1989 Effects of Caffeine on Vigilance Performance and Task-Induced Stress. Paper presented at the meeting of the Southern Society for Philosophy and Psychology, New Orleans, Louisiana.
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Rosa, and M.J. Colligan 1989 Effects of auxiliary load on vigilance performance in a simulated work environment.
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From page 170... ...
Lubin 1965 Signal uncertainty and sleep loss. Journal of Experimental Psychology 69:401407.
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