Multiscale entropy in a 10-minute vigilance task.

Research has shown multiscale entropy, brain signal behavior across time scales, to reliably increase at lower time scales with time-on-task fatigue. However, multiscale entropy has not been examined in short vigilance tasks (i.e., ≤ 10 min). Addressing this gap, we examine multiscale entropy during a 10-minute Psychomotor Vigilance Test (PVT). Thirty-four participants provided neural data while completing the PVT. We compared the first 2 min of the task to the 7th and 8th minutes to avoid end-spurt effects. Results suggested increased multiscale entropy at lower time scales later compared to earlier in the task, suggesting multiscale entropy is a strong marker of time-on-task fatigue onset during short vigils. Separate analyses for Fast and Slow performers reveal differential entropy patterns, particularly over visual cortices. Here, observed brain-behavior linkage between entropy and reaction time for slow performers suggests that entropy assays over sensory cortices might have predictive value for fatigue onset or shifts from on- to off-task states.

Gamma Power as an Index of Sustained Attention in Simulated Vigilance Tasks.

Performance on the psychomotor vigilance test (PVT; Dinges & Powell, 1985)-a common index of sustained attention-is affected by the opposing forces of fatigue and sustained effort, where reaction times and error rates typically increase across trials and are sometimes offset by additional efforts deployed toward the end of the task (i.e., an "end-spurt"; cf. Bergum & Klein, 1961). In ACT-R (Adaptive Control of Thought-Rational; Anderson et al., 2004), these influences on task performance have been modeled as latent variables that are inferred from performance (e.g., Jongman, 1998; Veksler & Gunzelmann, 2018) without connections to directly observable variables. We propose the use of frontal gamma (γ) spectral power as a direct measure of vigilant effort and demonstrate its efficacy in modeling performance on the PVT in both the aggregate and in individuals.

Vigilance end-spurt patterns in event-related potentials.

The end-spurt effect, where performance declines with time-on-task and then increases toward the end of a task, has garnered little attention in the vigilance literature. Researchers have suggested the performance enhancement is due to increased motivation or arousal with knowledge of the end of the vigil. However, recent examination of neural signature patterns during a simultaneous discrimination task, where task length was unknown, provided preliminary support that the end-spurt reflects pacing of resources. The current effort expands this previous work to an additional simultaneous task and to a successive discrimination task across two sessions, one where task length was not known and one where task length was known. Twenty-eight (Study 1) and a separate 24 (Study 2) participants completed a Simultaneous Radar task (Study 1) in one session and Simultaneous and Successive Lines tasks (Study 2) across two sessions while neural data was collected. Several event-related potentials exhibited non-monotonic patterns during the vigilance tasks, in some cases reflecting end-spurt patterns, but more commonly reflecting higher-order polynomial patterns. These patterns were more prevalent in anterior regions as opposed to posterior regions. Of note, the N1 anterior exhibited consistent general patterns across all the vigilance tasks and across sessions. Importantly, even when participants had knowledge of session length, some ERPs still exhibited higher-order polynomial trends, suggesting pacing rather than an end-spurt from motivation or arousal as the vigil ends. These insights can help inform predictive modeling of vigilance performance and the implementation of mitigation efforts to allay the vigilance decrement.