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Effects of Spatial Uncertainty on Auditory Vigilance Performance and Cerebral Hemodynamics

Vigilance is an individual’s ability to sustain attention for an extended period of time in order to detect infrequent, unpredictable events and is required in many settings to maintain performance efficiency and safety (Davies & Parasuraman, 1982). The risk of vigilance-related failures is amplified by the vigilance decrement, a decline in vigilance performance that typically occurs during vigilance tasks (Warm et al., 2008). Previous research indicates that task demands affect the time of onset and severity of the vigilance decrement such that increases in task demands magnify the performance decrement (Warm et al., 2008). Resource Theory accounts for these effects by arguing that vigilance tasks require limited-capacity information-processing resources that are depleted quicker than they can be replenished; and when the need for these resources exceeds their availability, performance begins to decline (Davies and Parasuraman, 1982). Neuroergonomic research methods provide additional support for resource theory by providing more direct evidence of the neurophysiological changes associated with the vigilance decrement. For example, transcranial Doppler sonography (TCD) indicates that cerebral blood flow velocity (CBFV) – a biomarker of neural activity – declines as performance declines (Warm & Parasuraman, 2007). Further, the rate of CBFV decline is increased as task demands are increased, a relationship that mirrors the relationship between task demands and the vigilance decrement (Warm & Parasuraman, 2007). For example, Funke and colleagues (2017) demonstrated that the increased task demands of spatial uncertainty, or uncertainty as to where signals will appear, in a visual vigilance task led to a larger decrease in performance and CBFV. This suggests that spatial uncertainty increases resource depletion and hinders performance in visual vigilance tasks. However, given that auditory spatial displays are also employed in operational settings that require vigilance, additional research is needed to determine whether spatial uncertainty impacts vigilance in the auditory modality. Previous research indicates that the processes and outcomes for vigilance are very similar for visual and auditory modalities. The occurrence of the decrement is observed in both modalities, and the task factors that amplify the decrement do so similarly in both modalities (See et al., 1995). Moreover, Shaw and colleagues (2009) showed that when visual and auditory vigilance tasks are equally difficult, they result in indistinguishable vigilance decrements, and CBFV also declines at the same rate in both modalities. Taken together, research comparing visual and auditory vigilance suggests that vigilance likely involves depletion of supramodal resources that are involved regardless of task modality. Thus, given that spatial uncertainty has a deleterious impact on performance in the visual modality, it seems likely that spatial uncertainty will also hinder vigilance performance in the auditory modality. The current study was designed to investigate that possibility by evaluating whether spatial uncertainty in auditory tasks leads to a more severe vigilance decrement and decline in CBFV. Data collection was delayed due to the COVID-19 pandemic and is ongoing. However, data collection is expected to be completed prior to the HFES 2021 conference in October. Forty participants will be recruited and randomly assigned to one of two conditions. In the spatial certainty condition, auditory stimuli will sound from speakers in a consistent, predictable spatial pattern. In the spatial uncertainty condition, auditory stimuli will sound from speakers in a random, unpredictable manner. All participants will complete a 40-minute vigilance task in their assigned condition. Performance and CBFV will be recorded. We expect that performance will be poorer and the vigilance decrement will be more severe in the spatial uncertainty condition, compared to the spatial certainty condition. Additionally, we predict that CBFV will decline more precipitously in the spatial uncertainty condition, than in the spatial certainty condition. This is based on the idea that CBFV indexes resource depletion, and depletion should be most severe in the more demanding spatial uncertainty condition.