Visual, Auditory, and Tactile Vigilance: The Effect of Sensory Modality on Vigilance Performance and Cerebral Hemodynamics

Vigilance tasks require an individual to sustain attention for an extended period of time in order to monitor for sporadic and unpredictable signals. A typical consequence of performing a vigilance task is a decline in performance throughout time on a task, known as the vigilance decrement. The vigilance decrement is a major concern as maintaining vigilance performance is essential to safety and system performance in a variety of operational settings. Vigilance tasks exist in operational settings as either visual, auditory, or tactile tasks. However, past research has been unable to determine conclusively whether sensory modality affects vigilance performance. Some research demonstrates that vigilance performance levels differ between modalities, which suggests that different modality-specific neurocognitive mechanisms may support vigilance performance in each sensory modality. By contrast, other research has shown that performance is equivalent across sensory modalities, which supports the view that the same supramodal neurocognitive mechanisms are used for vigilance, regardless of task modality. The divergent findings in past research may have been due to variable and inadequate crossmodal matching procedures. Specifically, it is possible that the studies that observed differences between modalities failed to control for variables that could confound modality comparisons (e.g., stimulus discriminability, stimulus intensity). Support for this concern comes from studies that matched modalities for possible confounding differences; between-modality performance differences were reduced or eliminated. Unfortunately, the crossmodal matching methods used in past research may not have effectively eliminated confounds. There is some direct evidence of failures of crossmodal matching efforts, and studies using the same crossmodal matching methods have provided very different conclusions about whether modality affects vigilance performance. The aim of this dissertation was to improve upon the crossmodal matching methods in previous research to determine whether mean vigilance performance levels and the severity of the vigilance decrement are similar or different between visual, auditory, and tactile modalities. Measurement of cerebral hemodynamics was used to further inform whether the neurocognitive mechanisms governing vigilance performance are supramodal or modality-specific. The findings of the current study suggest that methods used to equate sensory modalities addressed issues that may have led to the controversy in findings of previous vigilance research. Performance and cerebral blood flow velocity (CBFV) results were all equivalent across the crossmodally-equated visual, auditory, and tactile vigilance tasks, suggesting that mainly supramodal neurocognitive mechanisms govern vigilance performance. These findings suggest that vigilance tasks may be designed in different sensory modalities without concern for differential effects on performance between modalities. However, future research should investigate the extent to which modality-specific differences in variables that were addressed in this dissertation (e.g., stimulus discriminability, stimulus intensity) may still affect performance in operational settings. These findings also suggest that tracking the neurophysiological dynamics associated with vigilance using CBFV may be possible regardless of sensory modality. Future research should investigate the effectiveness of other neuroimaging methods in tracking the neurophysiological dynamics associated with vigilance across sensory modalities.