Sustained Visual Attention During Simultaneous and ... - SAGE Journals

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SUSTAINED VISUAL ATTENTION DURING SIMULTANEOUS AND SUCCESSIVE VIGILANCE TASKS P.A. Desmond, G. Matthews, & J. Bush A study of sustained visual attention during simultaneous and successive vigilance task paradigms is reported. 50 participants completed a simultaneous sensory vigilance task with a low event rate, and 50 different participants completed a successive sensory vigilance task with a low event rate. In the simultaneous task participants were presented with pairs of digit-like stimuli on a PC monitor display, and were asked to detect when one of the stimuli was slightly smaller than the other stimulus. In the successive task version participants were required to compare the size of the currently viewed digit pair with the previously presented stimuli, requiring use of memory to detect the target. All participants completed a variety of subjective measures of stress states before and after the vigilance task. The results indicated that the vigilance decrement was greater for sensory simultaneous than for sensory successive tasks. Practical implications of the study are discussed. INTRODUCTION Studies of vigilance have suggested that task discrimination type is an important determinant of the vigilance decrement (e.g. See et al, 1995). Parasuraman and Davies (1977) have made a distinction between simultaneous and successive vigilance tasks. In successive discrimination tasks, observers are required to discriminate between a currently viewed stimulus and a standard representation of a specific stimulus held in working memory. For example, observers might be asked to judge if the size of a currently presented letter is the same or different compared to the size of a previously presented letter. In simultaneous tasks, all of the critical information required to make the discrimination between stimuli is presented in the current field. For example, observers might be asked to indicate whether two letters presented simultaneously are of the same size. Taxonomic analyses of vigilance have shown that the nature of the discrimination is a key factor controlling perceptual sensitivity decrement (Warm & Dember, 1998). Successive tasks are more likely to show decrement than simultaneous tasks, especially when event rate is high. Successive tasks are believed to require more attentional resources than simultaneous tasks, so that vigilance decrement is a consequence of resource depletion over time.

Consistent with this view, other task factors that increase attentional demand also tend to increase the magnitude of the decrement (Warm & Dember, 1998). See et al. (1995) conducted a meta-analysis of vigilance studies that investigated the role of task factors in controlling the incidence and magnitude of sensitivity decrement. In general, results confirmed taxonomic analyses, in showing that the magnitude of the decrement ('effect size') increases with task demand factors including successive discrimination and high event rate. However, a regression model of influences on effect size suggested that effects of task factors differ for sensory tasks, in which the target is defined by perceptual attributes such as size, versus cognitive tasks, in which target detection requires some symbolic encoding of data (e.g. detecting a sequence of three odd numbers). For cognitive tasks, effect sizes were larger for successive tasks than for simultaneous tasks at all event rates, although the difference was more pronounced at low event rates, a finding generally consistent with an attentional resource model. For sensory tasks, the effect size was again higher for successive tasks at high event rates, as expected, but, at low event rates, simultaneous tasks showed greater decrement than successive tasks, contrary to expectation. Thus, the vigilance decrement is not restricted to a

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successive task with a high event rate; a decrement can also be found with sensory simultaneous vigilance tasks that have a low event rate. This finding may be practically significant in human factors. The thrust of most of the work on vigilance decrement is that tasks requiring sustained monitoring should be designed to reduce the high levels of task demand that seem to elicit loss of perceptual sensitivity. However, the See et al. (1995) meta-analysis implies that this strategy may be misguided in the case of sensory simultaneous tasks; the regression model predicted greater effect size for the decrement as event rate is reduced. The meta-analysis, of course, detects relationships in studies already run, often for purposes other than comparing simultaneous and successive task performance. Thus, it is important to test that the effect is reliable, and not an accident of averaging data from studies that did not seek to test the effect of discrimination type explicitly. The primary aim of the present experiment was thus to examine the vigilance decrement using successive and simultaneous sensory vigilance tasks that have low eventrates, A subsidiary aim was to test whether the tasks used provoked similar subjective stress responses. Previous studies have shown that vigilance tasks are often stressful, eliciting feelings of tiredness, demotivation and emotional distress (e.g. Szalma et al., 1999). Differences in stress response to simultaneous and successive tasks might contribute to differential decrement, Method Participants: One hundred Texas Tech students participated in the study (50 males and 50 females). Mean age was 20.6. Participants were given course credit for participating in the experiment, Subjective Measures: Participants completed the Dundee Stress State Questionnaire (Matthews, Joyner, Gilliland, Campbell, Huggins & Falconer, 1999) before and after task completion. The DSSQ is a reliable, validated scale that measures mood, cognition and motivation. Part 1 of the DSSQ is a 29-item mood scale, the UMACL (Matthews et al., 1990) which assesses major components of mood

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including EA (energetic arousal), TA (tense arousal) and Hedonic Tone (HT). The second part of DSSQ assesses motivation using a 22-item scale. These items measure Success motivation and Intrinsic motivation. Part 3 of DSSQ is a measure of cognitive components of the stress state; it assesses general thinking style and task beliefs. It includes scales for self-focused attention, self-esteem, concentration and confidence and control. Part 4 of DSSQ measures cognitive interference or specific intruding thoughts. It has 10 items relating to taskrelevant interference and 11 items related to taskirrelevant personal interference. Experimental Tasks."Tasks used were similar to those used by Deaton and Parasuraman (1993), comparing detection of cognitive and sensory stimuli for vigilance decrements. In their sensory task, subjects were presented with digit-like stimuli on a PC monitor display; and were asked to respond by pressing a key when one of the stimuli was slightly smaller than the other. This is a simultaneous sensory task. A successive version of the sensorytaskwasalsoused.Again,pairsof stimuli were presented, but, on positive trials, both stimuli were slightly smaller than the standard size, requiring a comparison with the previous trial or memory representation. All tasks had an event rate of 10 stimuli/minute, a rate classified by See et al. (1995) as low. Signal probability of both tasks was 0.10. Tasks comprised of six 8-minute periods, making the total duration 48 minutes. Each period contained 8 target stimuli. The discrimination type (successive vs.simultaneous) variablewas manipulated between-subjects. The experimental session lasted for about two hours. Procedure: Participants completed the DSSQ on arrival at the laboratory. They completed a seriesof practicevigilancetasksin whichthesize difference between targets and nontargets was systematically manipulated. The objective was to have participants performing simultaneous or successive tasks of roughly equivalent difficulty, aiming for a moderate difficulty level represented by a P(A) value of 0.90. (P(A) is a measure of perceptual sensitivity that makes fewer assumptions than the d' index derived from Signal Detection Theory). Hence, discrimination difficulty was set

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individually for each participant, to the value that gave the P(A) value closest to 0.90. After this task calibration, participants completed the main vigilance task (either successive or simultaneous), after which participants completed a post-task version of the DSSQ. RESULTS The data were analyzed using a 2 (discrimination type: successive vs. simultaneous) x 6 (six blocks of time) analysis of variance with correct detections (hits) and P(A) as dependent measures (see Table 1). For both indices, there was a significant main effect of Block (p