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Cerebral Blood Flow Velocity and Task Engagement as Predictors of. Vigilance Performance. Lauren E. Reinerman, Gerald Matthews, Joel S. Warm, Lisa K.
PROCEEDINGS of the HUMAN FACTORS AND ERGONOMICS SOCIETY 50th ANNUAL MEETING—2006

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Cerebral Blood Flow Velocity and Task Engagement as Predictors of Vigilance Performance Lauren E. Reinerman, Gerald Matthews, Joel S. Warm, Lisa K. Langheim, Kelley Parsons, Christina A. Proctor, Tazeen Siraj, Lloyd D. Tripp and Robert M. Stutz University of Cincinnati Cincinnati, Ohio Responses to a brief six-min screening battery involving high-workload tracking, verbal working memory, and line discrimination tasks were used to predict subsequent performance on a 36-min vigilance task. Two predictors of interest were subjective state, as indexed by the Dundee Stress State Questionnaire (DSSQ), and cerebral blood flow velocity (CBFV), measured via transcranial Doppler sonography. The results testify to the importance of assessing task-induced responses for predicting vigilance performance. They also indicate that forecasting vigilance performance is a complex endeavor requiring a set of multidimensional predictors. Specifically, higher post-battery task engagement scores on the DSSQ in this study and higher levels of CBFV in the left hemisphere during performance of the screening battery predicted more correct detections on the subsequent vigilance task. These findings are interpreted in the light of the resource-workload model of vigilance, and their practical significance is discussed.

Vigilance or sustained attention is a principal element of human performance in a wide range of activities such as air traffic control, airport security, industrial quality control, and cytological screening (Warm, Dember, & Hancock, 1996). Although vigilance is essential to many important jobs, procedures for the selection of personnel to fulfill positions requiring sustained attention are ineffective. Traditional criteria for predicting sustained performance efficiency such as age, sex, sensory acuity, and personality measures have limited utility, in that their correlations with vigilance are often small and inconsistent across studies (Davies & Parasuraman, 1982). The present study attacked the issue of selection for vigilance with a strategy designed to tailor the identification of predictive factors to the information processing demand imposed by vigilance tasks. Although vigilance tasks have traditionally been viewed as understimulating assignments that impose little workload upon observers, studies using the NASA-Task Load Index to assess the perceived mental workload of sustained attention have revealed that the cost of mental operations in vigilance is substantial and mentally demanding (Warm et al., 1996). Such observations support a resource model of vigilance that attributes the vigilance decrement to progressive loss of information-processing resources (Johnson & Proctor, 2004). Thus, our ability to develop predictive measures of vigilance performance may be improved by assessment of individual differences in resource availability (Matthews, Davies & Holley, 1993). The strategy adopted in this study was to expose observers to a short, potentially stressful battery of high information-processing demand tasks. Response to the battery was then used for assessment of resource availability, providing a basis for predicting subsequent vigilance task performance. Three types of response were considered to be promising as indices of resources. One is cerebral blood flow velocity (CBFV) measured via transcranial Doppler

ultrasonography (TCD). The second is subjective state measured by the Dundee Stress State Questionnaire (DSSQ). The third was cortisol, assayed from saliva, that may index activity in the hypothalamic-pituitary axis (HPA: Kirschbaum & Hellhammer, 2000) activated by stressors. Subjective states of stress and fatigue may be assessed using the DSSQ (Matthews et al., 2002), which measures three broad factors that integrate affect, motivation, and cognition. The dimensions are Task Engagement which incorporates energetic arousal, motivation, and concentration, Distress which encompasses negative moods and lack of confidence, and Worry which reflects level of intrusive thoughts and other negative self-referent cognitions. Previous studies have shown that task engagement is reliably predictive of vigilance and other attentionally demanding tasks (Matthews et al., 2000). This state factor may index resource availability. Performance of vigilance tasks typically leads to loss of task engagement over time, accompanied by increasing distress (Matthews et al., 2002; Szalma et al., 2004), a state change that may contribute to vigilance decrement. Thus, it was hypothesized that observers’ levels of task engagement following performance of the short battery would serve as a useful predictor of later vigilance performance. Transcranial Doppler ultrasonography is a noninvasive procedure that allows continuous monitoring of blood flow in the left and right medial cerebral arteries during task performance. Studies conducted in our laboratory have shown that vigilance tasks provoke an increase in CBFV that is closely tied to the information-processing demand of the tasks involved (Hitchcock et al., 2003; Warm & Parasuraman, in press). Such findings suggest that CBFV may serve as an index of the utilization of attentional resources during vigilance. Since CBFV has been found to vary directly with information-processing demand in a wide variety of other tasks (Stroobant &Vingerhoets, 2000), it was also hypothesized that the level of CBFV secured from observers

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PROCEEDINGS of the HUMAN FACTORS AND ERGONOMICS SOCIETY 50th ANNUAL MEETING—2006

on the short battery would predict detection rate on a subsequent attentionally demanding vigilance task. Much work on the psychoendocrinology of stress has focused on the hormone cortisol. Its release is associated with activity of a 'hypothalamic-pituitary-adrenal axis' (HPA) that has an acute 'proactive' role in mobilizing energy and physiological defense mechanisms (Kirschbaum & Hellhammer, 2000). During vigilance, high cortisol correlates with electroencephalographic indices of stress and alertness (Born et al., 1988), but the functional significance of the cortisol response for performance remains to be determined.

utilizing a simulated air-traffic control display in which two planes, represented by black lines, flew over a city, symbolized by a red circle. Normally, the “planes” were on a non-collision course, one passing over the center of the “city” and one on a tangent to the “city.” Critical events for detection were cases in which the “planes” flew on a collision path over the center of the “city.” Participants indicated their detection of collision paths by pressing the spacebar on a computer keyboard. A final administration of the DSSQ was given following the vigil. A second saliva sample was provided at this time. Samples were subsequently assayed for cortisol at an external laboratory (Salimetrics, LLC, State College, PA).

METHOD RESULTS Participants Manipulation Checks

Design Experimental sessions were composed of three phases: an acclimation phase, an initial performance phase featuring a short battery of tasks, and a final vigilance performance phase. Task engagement, distress, and worry were measured by the DSSQ (Matthews et al., 2002). During all phases of the experimental session, continuous CBFV in the right and left medial cerebral arteries was recorded simultaneously by a Nicolet Companion III TCD unit with two transducers fitted within a head bracket worn by the observer. Saliva samples were taken by having participants chew on a cotton wool swab following both performance phases. Procedure Observers were tested individually in a quiet laboratory room. Upon arrival for the experiment, they completed a pre-test version of the DSSQ and were acclimated to the TCD recording procedure during a 2-min resting baseline in which they were asked to relax while gazing at a blank visual display terminal. All subsequent CBFV scores were expressed as a proportion of the mean resting baseline value (Stroobant & Vingerhoets, 2000; Warm & Parasuraman, in press). After the introductory phase, observers completed the initial performance phase which included: (1) a tracking task in which a joystick was used to keep a crossbar centered on a line, (2) a working memory task that required observers to keep words in memory while solving math problems, and (3) a line discrimination task in which observers detected lines of longer length that occurred occasionally in a series of successive lines. Tasks were configured to be highly demanding. Each of the tasks lasted for 2 min with a 2-min inter-task interval. Immediately after completing a post-battery DSSQ, and providing a saliva sample, observers completed a continuous 36-min vigilance task (Hitchcock et al., 2003),

Several analyses were conducted to ensure that the tasks elicited the expected behavioral and CBFV responses. First, comparisons of pre-test DSSQ scores with post-task short battery and vigilance DSSQ scores confirmed that both performance phases were stressful. DSSQ distress was elevated relative to its initial baseline level following both performance phases. The change from baseline was +1.42 SD for the short task battery, and +0.95 SD for the vigilance task. DSSQ task engagement following the vigilance task was depressed below baseline by -1.58 SD. Task engagement did not change significantly following the short battery. Thus, only the vigilance task appeared to be fatiguing. Second, the short task battery elicited increases in CBFV resembling those seen in other research (Stroobant & Vingerhoets, 2000), as shown in Figure 1. A 3 x 2 (task x hemisphere) ANOVA, with repeated measures on both factors, demonstrated that the main effect of task was significant (F(2,288) = 17.91, p