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Mental effort affects vigilance enduringly: after-effects in EEG and behavior

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Abstract

Vigilance is assumed to decline with sustained task performance. The EEG-effects during performance on mental tasks, however, cannot be ascribed indisputably to vigilance decline per se. During task performance itself, effects of information processing and vigilance decline may be confounded. In this study, effects of sustained mental effort were studied in the absence of specific information processing, after sustained information processing had taken place, namely after an effortful 70-min intelligence test. Vigilance was determined by means of EEG-measures in a rest condition. Furthermore, behavioral performance was assessed on two different tasks, the traditional Clock test and the SART. After mental effort, theta power in the EEG and errors on the SART were increased. Beta2 power, however, also appeared enhanced. We conclude that sustained mental effort produces an enduring decrease in vigilance, but that some active processing is enhanced at the same time. A second study replicated the EEG-results after mental effort.

Section snippets

Participants

Forty healthy students (10 men and 30 women; mean age 23 years) participated in this study. They all signed an informed consent and could choose between €20, − or course credits.

Statistical analyses

Data were statistically analyzed with repeated-measures ANOVAs with Bonferroni's confidence interval adjustments. FFT data were analyzed with a 2×2 (time×condition) ANOVA. Behavioral data were computed with a 2×2 (part of task×condition) ANOVA.

Vigilance measures—EEG data: spectral power (FFT)

Merely results for theta and beta2 are presented (see Table 1), as no relevant effects were found for the other bands. Furthermore, results are not presented for Fz, as there were no significant effects present. Separate analyses were performed for the

Discussion

In both experiments, theta power in the EEG increased after mental effort, which indicates a vigilance lowering Ballard, 1996, Corsi-Cabrera et al., 1996, Matthews et al., 2000, Paus et al., 1997. Furthermore, performance declined on the SART after the mental effort task in the first experiment. This decrement is also regarded as a vigilance decline Ballard, 1996, Gillberg and ′kerstedt, 1998, Gorissen et al., 1997. The SART was more sensitive than the Clock test for the effects of mental

Acknowledgements

We thank Natasja Verbocht for assistance during the experiment, Willie van Schaijk for general technical guidance and programming of software concerning EEG-analyses, and Hubert Voogd for constructing software of the SART and Clock test.

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