Joel S. Warm

Enhancing vigilance in operators with prefrontal cortex transcranial direct current stimulation (tDCS).

Sustained attention, often referred to as vigilance in humans, is the ability to maintain goal-directed behavior for extended periods of time and respond to intermittent targets in the environment. With greater time-on-task the ability to detect targets decreases and reaction time increases-a phenomenon termed the vigilance decrement. The purpose of this study was to examine the role of dorsolateral prefrontal cortex in the vigilance decrement. Subjects (n=19) received prefrontal transcranial direct current stimulation (tDCS) at one of two different time points during a vigilance task (early or late). The impact of tDCS was examined using measures of behavior, hemispheric blood flow velocity, and regional blood oxygenation relative to sham stimulation. In the sham condition greater time-on-task was accompanied by fewer target detections and slower reaction times, indicating a vigilance decrement, and decreased blood flow velocity. tDCS significantly altered baseline task-induced physiologic and behavioral changes, dependent on the time of stimulation administration and electrode configuration (determining polarity of stimulation). Compared to the sham condition, with more time-on-task blood flow velocity decreased less and cerebral oxygenation increased more in the tDCS condition. Behavioral measures showed a significant improvement in target detection performance with tDCS compared to the sham stimulation. Signal detection analysis revealed a significant change in operator discriminability and response bias with increased time-on-task, as well as interactions between time of stimulation administration and electrode configuration. Current density modeling of tDCS showed high densities in the medial prefrontal cortex and anterior cingulate cortex. These findings confirm that cerebral hemodynamic measures provide an index of resource utilization and point to the central role of the frontal cortex in vigilance. Further, they suggest that modulation of the frontal cortices-and connected structures-influences the availability of vigilance resources. These findings indicate that tDCS may be well-suited to mitigate performance degradation in work settings requiring sustained attention or as a possible treatment for neurological or psychiatric disorders involving sustained attention.

Predicting vigilance: A fresh look at an old problem

Individual differences in vigilance are ubiquitous and relevant to a variety of work environments in industrial, transportation, medical and security settings. Despite much previous work, mostly on personality traits, it remains difficult to identify vigilant operators. This paper reviews recent research that may point towards practically useful predictor variables for vigilance. Theoretical approaches to identifying predictors that accommodate the heterogeneous nature of vigilance tasks are compared. The article surveys recent empirical studies using personality measures, ability tests and scales for stress and coping as predictors of vigilance. Promising new constructs include trait scales linked to fatigue, abnormal personality and the stress state of task engagement. Implications of the data reviewed for occupational selection are discussed. Selection should be based on a multivariate assessment strategy, cognitive task analysis of the operational vigilance task and use of work sample measures to capture typical stress responses to the task. This review paper surveys recent research that may point towards practically useful predictor variables for vigilance. The article surveys recent empirical studies using personality measures, ability tests and scales for stress and coping as predictors of vigilance. Selection should be based on a multivariate assessment strategy.

Further Tests of an Abbreviated Vigilance Task: Effects of Signal Salience and Jet Aircraft Noise on Performance and Stress

The effects of signal salience and jet-aircraft noise on performance and self-reports of stress were examined in an abbreviated vigilance task (12 min) that duplicates many of the findings with longer duration vigilance tasks (Temple et al., 2000). As is the case with longer vigils, signal detection in the abbreviated task was poorer for low salience than for high salience signals and stress scores, as indexed by the Dundee Stress State Questionnaire (Matthews, Joiner, Gilliland, Campbell, & Falconer, 1999), were generally greater when observers were required to detect low as compared to high salience signals. Unlike longer vigils, however, signal detection in the abbreviated task was superior in the presence of noise than in quiet, and noise generally attenuated self-reports of stress. The beneficial effect of jet-aircraft noise for the abbreviated task differentiates it from longer vigilance tasks and suggests that noise may have short-term positive value in vigilance.

Effect of Active and Passive Fatigue on Performance Using a Driving Simulator

The present study investigated the effects of active fatigue (e.g., elevated distress) and passive fatigue (e.g., decreased task engagement) on driving performance. The study used similar manipulations developed by Saxby et al. (2007), which were shown to induce active and passive fatigue states. 168 undergraduates participated. There were 3 conditions (active, passive, control) and 2 durations (10, 30 minutes). The active condition used simulated wind gusts to increase the required number of steering and acceleration changes, while the passive condition was fully automated. In the control condition, drivers were in full control of steering and acceleration. Data confirmed that, over time, passive fatigue is expressed as decreasing task engagement. Furthermore, drivers in the passive condition had slower response times to an unexpected event and were more likely to crash than those in the active and control conditions. Theoretical and practical implications are discussed.

Development of Active and Passive Fatigue Manipulations Using a Driving Simulator

The present study investigates driving simulator methodologies for inducing qualitatively different patterns of subjective response. The study tested Desmond and Hancocks (2001) theory that there may be two types of fatigue: active and passive. 108 undergraduates participated. There were 3 conditions (active, passive, control) and 3 durations (10, 30, 50 minutes). The active condition used simulated wind gusts to increase the required number of steering and acceleration changes. The passive condition was fully automated. In the control condition, drivers were in full control of steering and acceleration. Task engagement (e.g., energy) was lowest in the passive fatigue condition, followed by the control and active conditions. Distress (e.g., negative mood) was found to be highest in the active fatigue condition. The time course of fatigue responses was also determined. The results suggest methods for developing manipulations to determine the impact of fatigue on performance.

Target Acquisition with UAVS: Vigilance Displays and Advanced Cueing Interfaces

Future Uninhabited Aerial Vehicles (UAVs) will require operators to switch quickly and efficiently from supervisory to manual control. Utilizing a vigilance task in which threat detections (critical signals) led observers to perform a subsequent manual target acquisition task, the present investigation revealed that the type of vigilance display might have important design implications for future UAV systems. A sensory display format resulted in more threat detections, fewer false alarms, and faster target acquisition times and imposed a lighter workload than a cognitive display format. Thus, the former may be the best display arrangement for future UAV controllers. Additionally, advanced visual, spatial audio, and haptic cueing interfaces enhanced acquisition performance over no cueing in the target acquisition phase of the task, and did so to a similar degree. This finding suggests that advanced cueing interfaces may also prove useful in future UAV systems and that these interfaces are functionally interchangeable.

Effects of Stereoscopic Depth on Vigilance Performance and Cerebral Hemodynamics.

Objective: We tested the possibility that monitoring a display wherein critical signals for detection were defined by a stereoscopic three-dimensional (3-D) image might be more resistant to the vigilance decrement, and to temporal declines in cerebral blood flow velocity (CBFV), than monitoring a display featuring a customary two-dimensional (2-D) image. Background: Hancock has asserted that vigilance studies typically employ stimuli for detection that do not exemplify those that occur in the natural world. As a result, human performance is suboptimal. From this perspective, tasks that better approximate perception in natural environments should enhance performance efficiency. To test that possibility, we made use of stereopsis, an important means by which observers interact with their everyday surroundings. Method: Observers monitored a circular display in which a vertical line was embedded. Critical signals for detection in a 2-D condition were instances in which the line was rotated clockwise from vertical. In a 3-D condition, critical signals were cases in which the line appeared to move outward toward the observer. Results: The overall level of signal detection and the stability of detection over time were greater when observers monitored for 3-D changes in target depth compared to 2-D changes in target orientation. However, the 3-D display did not retard the temporal decline in CBFV. Conclusion: These results provide the initial demonstration that 3-D displays can enhance performance in vigilance tasks. Application: The use of 3-D displays may be productive in augmenting system reliability when operator vigilance is vital.

Stress and Workload Profiles of Network Analysis: Not All Tasks Are Created Equal

Effective cyber defense depends upon intrusion detection, i.e., the process of monitoring, detecting, and reacting appropriately to cyber activity threatening network security. Intrusion detection requires the execution of multiple unique, interdependent network analysis tasks. The current study aimed to expand understanding of cyber defense by separately assessing task induced workload and stress for two key network analyst tasks, triage analysis and escalation analysis, which are the first and second lines of cyber defense, respectively. In separate studies, participants assumed the role of either a triage analyst or an escalation analyst, performed associated intrusion detection duties in simulated cyber task environments, and reported task induced workload and stress. Findings suggest that, even though triage and escalation analysts are both engaged in cyber defense, their tasks result in differentiable workload and stress profiles. This highlights the need for further human factors research examining operator performance and state across network analyst roles.

Detection-Action Linkage in Vigilance: Effects on Workload and Stress

Using a simulated UAV control task in which a vigilance display warned observers of the presence of enemy threats, Gunn et al. (2005) reported that perceived mental workload in relation to the vigilance task was unexpectedly low. The present study did not confirm that finding. It did show, however, that vigilance performance was greater and task induced stress was less among observers who had the opportunity to act upon vigilance signal detections by destroying the enemy threats than among those who detected threats but had no opportunity to counter them. Accordingly, the results point to the importance of a detection-action linkage to enhance signal detection and reduce stress in the performance of vigilance tasks.

Predicting Cognitive Vigilance Performance from Cerebral Blood Flow Velocity and Task Engagement

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 cognitive 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 ultrasonography. The results testify to the importance of assessing task-induced responses for predicting cognitive 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 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.