Is Neuroergonomic Monitoring Non-Intrusive? An Examination of Transcranial Doppler Sonography
Authors: Greenlee Eric T. , Lui Tiffany G. , Maw Emily L. 
Published: September 2018

One of the primary aims of neuroergonomic research is to identify neural and psychophysiological measures that can be used to index operator state in real time (e.g., Stephens, Scerbo, & Pope, 2012; Tripp & Warm, 2007). Such measures are desired because they may have capabilities that exceed traditional subjective and performance methods of estimating operator state. Physiological monitoring has been proffered as a remedy for the shortcomings of subjective and performance measures of operator state, because it is arguably less intrusive than subjective measures, allows for continuous measurement, and provides estimates of operator state even when performance efficiency is unobservable (Stephens et al., 2012). One area where physiological monitoring may be particularly beneficial is within tasks that require vigilance. Vigilance tasks are common within many military, industrial, and medical settings and generally require an operator to maintain attentional focus for the detection of critical events that tend to occur rarely and unpredictably. However, the ability to maintain vigilance typically declines over time, which is problematic when detection is critical to system safety. Additionally, the demands of vigilance tasks are associated with high workload and task-induced stress (Warm, Parasuraman, & Matthews, 2008). Research suggests that physiological measures may allow for continuous, real-time tracking of an operator’s level of vigilance, and facilitate adaptive interventions (e.g., rest breaks, adaptive automation) to ensure that a loss of vigilance does not lead to errors or accidents (Warm & Parasuraman, 2007). Transcranial Doppler Sonography (TCD) is a physiological measure that is especially well-suited to real-time assessment of operator vigilance (Warm & Parasuraman, 2007). TCD can be used to monitor hemodynamic activity within the brain, which has been closely linked to level of vigilance performance. In short, TCD may serve to predict and prevent loss of vigilance, non-intrusively in operational settings (Warm & Parasuraman, 2007). Before deploying TCD for vigilance monitoring in operational settings users should consider whether it is truly non-intrusive. If TCD monitoring negatively impacts operator state or performance, practical applications may be limited. The current study was designed to determine whether TCD use has intrusive effects on operator state and performance. To assess operator state, we utilized three measures that have been used previously in vigilance tasks: The Short Stress State Questionnaire (SSSQ; Helton, 2004), the Simulator Sickness Questionnaire (Kennedy, Lane, & Berbaum, 1993), and the NASA-TLX. These questionnaires were used to assess task-induced stress, symptoms of simulator sickness, and workload, respectively. Performance was assessed in terms of percentage correct detections. Forty-two students (34 Women, 8 Men) were assigned at random to either a Doppler Monitoring condition or to a Control (No Physiological Monitoring) condition with the restriction that the group size (n = 21) and the ratio of participant sex be identical in both conditions. All participants completed a 40-minute vigilance task based on the procedure used by Greenlee and colleagues (2015), wherein participants monitored a computerized gauge for cases in which the gauge needle deviated from a vertical position (20% signal probability, 50 events per minute). Participants in the Doppler Monitoring condition wore the TCD during the vigil, those in the Control condition did not. Results from both conditions mirror typical vigilance findings. Percentage correct detections declined over time, distress and symptoms of simulator sickness increased, engagement decreased, and workload was rated as high. However, the performance, task-induced stress, reported levels of simulator sickness, and workload of participants equipped with TCD were indistinguishable from values taken from participants in the control condition. With the caveat that these are statistically null results, this supports the possibility that TCD monitoring may be non-intrusive. This finding, combined with research demonstrating the link between TCD measurements and vigilance (e.g., Warm & Parasuraman, 2007), supports the recommendation that TCD should be used in operational settings where operator vigilance is of paramount importance.