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Mentally fatigued persons switch to automatic pilot

May 23, 2002

Mentally fatigued trial subjects search less systematically for solutions than fit colleagues. Such fatigued persons switch to an automatic pilot approach even when this repeatedly leads to the same mistakes.

Psychologists from the University of Amsterdam studied how purposefully mentally fatigued persons conducted themselves. Healthy persons and persons made mentally tired were subjected by the scientist to various tests. The tests revealed that fatigued persons had difficulty in translating objectives into the associated actions. The mentally fatigued person was less flexible, more persistent in his behaviour and had a lack of self-regulation.

In one of the tests the trial subjects had to change the layout of a table in the computer programme Excel. The persons had never previously worked with Excel and were given an example of the end result on paper. The persons had to think aloud whilst carrying out the task. Their actions were registered by the computer and recorded on video.

Prior to the test, half of the trial subjects were made mentally tired. They had to draw up schedules for two hours. The other half of the trial subjects was allowed to relax for two hours.

Mentally fatigued persons worked less systematically than non-fatigued persons. They also repeatedly tried the same options, even when it was clear for a long time that this action did not work. Furthermore the fatigued trial subjects guessed more often than their non-fatigued colleagues. The fit trial subjects sought purposefully and quickly learnt from their mistakes.

The mentally fatigued persons also scored less well in two standard psychological tests than the fit persons. For example, fatigued persons needed more time to carry out the first manoeuvre in a mind game. Furthermore, it took them longer to realise that the rules of the game had been surreptitiously changed.

A fourth test investigated whether trial subjects had control over their actions. Fatigued persons were just as good as their fit colleagues at substituting a standard action with an alternative. However, fatigued persons often responded more slowly. This is probably due to so-called `lapses in control`, periods in which the control of ones actions is temporarily non-active. Such periods also occur among fit persons but with a lower frequency.

One of the lessons from this study is that the manufacturers of devices and computer programmes need to make these as logical as possible. Fatigued persons who switch to automatic pilot will then make a minimum of mistakes.

NWO (Netherlands Organization for Scientific Research)