Lapses in Alertness: Brain-Evoked Responses to Task-Irrelevant Auditory Probes

Abstract : Thirteen subjects participated in an auditory simulation of a passive sonar target detection environment. Targets were 300 ms noise bursts presented at near threshold levels in a noise background at a mean rate of 10 per minute. Task irrelevant probe tones were also presented at inter-stimulus intervals of 2-4 seconds. Each subjects participated in two 28 minute test sessions, pressing a button whenever they detected a noise target. Prominent minute-scale fluctuations in performance (computed as changes in local error rate using a 32- s moving window) occurred in many of the sessions. Evoked responses to the irrelevant probe tones in thirteen runs with highest number of performance lapses were sorted by current local error rate and smoothed using a moving- average. The amplitude of the grand mean N2 response to the irrelevant probe tones increased monotonically with error rate. Averaged evoked responses to relatively frequent, task-irrelevant probe tones appear to allow an accurate estimate of level of alertness if adequate number of trials are available.

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