Mental and physical effort affect vigilance differently

https://doi.org/10.1016/j.ijpsycho.2005.02.001Get rights and content

Abstract

Both physical and mental effort are thought to affect vigilance. Mental effort is known for its vigilance declining effects, but the effects of physical effort are less clear. This study investigated whether these two forms of effort affect the EEG and subjective alertness differently. Participants performed a physical task and were subsequently presented with a mental task, or vice versa. Mental effort decreased subjective alertness and increased theta power in the EEG. Both results suggest a vigilance decline. Physical effort, however, increased subjective alertness and alpha and beta1 power in the EEG. These findings point towards an increase in vigilance. Beta2 power was reduced after physical effort, which may reflect a decrease in active cognitive processing. No transfer effects were found between the effort conditions, suggesting that the effects of mental and physical effort are distinct. It is concluded that mental effort decreases vigilance, whereas physical effort increases vigilance without improving subsequent task performance.

Section snippets

Participants

Participants were 44 healthy students (8 men and 36 women; mean age 22 years). They signed an informed consent and received 20 or fulfilled a course requirement.

Recording

Electrodes were placed at Fz, Cz, and Pz (Jasper, 1958). EEG was registered with Ag–Cl electrodes in an elastic cap. The ground electrode was placed on the forehead and the left mastoid served as reference. Electro-ocular activity was recorded next to and above the right eye. Electrode impedance was less than 5 kΩ. Signals were

Results

Data were analyzed with repeated measures ANOVAs with Bonferroni's confidence interval adjustments. EEG data were analyzed per electrode site with 3 × 3 × 2 (Group × Time × Eyes situation: open or closed) ANOVAs. In case of an occasional missing value for the EEG data the missing value was replaced by its group mean (there was less than 1 missing data point per participant per electrode site over the entire experiment). Performance and HR data of each measurement were split in two (part 1 and part 2)

Discussion

Any mental task that requires a response entails a physical component. Moreover, it is known that physical exercise concerns a central element as well (Gandevia, 2001, Nielsen and Nybo, 2003). However, we argue that a sustained mental task condition in which relatively little muscular movement is needed, will primarily require a vast amount of central energy expenditure. Conversely, a physical effort task will lead to far more peripheral energy costs if it predominantly requires body movements

Acknowledgements

We would like to thank Anneke Mol and Peter Staal for their assistance during the experiment. We are grateful for the general technical guidance of Willy van Schaijk and Jos Wittebrood. We thank Hubert Voogd for constructing software for the mental effort task and Philip van den Broek for support with respect to EEG analyses.

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