Universiteit Leiden

Is exerting mental effort always good for performance?

Is exerting mental effort always good for performance? 'Close up of The Thinker' by Brian Hillegas

One would think that more information and more mental effort should lead to faster and better performance. However, a recent finding shows that people can in fact overthink their highly automatic skills by exerting mental effort.

A common assumption in psychology and cognitive neuroscience is that more information and more mental effort should lead to faster and better performance in a variety of cognitive tasks. However, Bernhard Hommel and I have recently discovered an intriguing experimental finding suggesting that this may not always be the case. In a set of laboratory experiments we observed that exerting too much cognitive control can under certain circumstances impair performance.

We designed various computer tasks in which participants were required to press a right or left button depending on the stimulus that was presented. In one of the tasks the instructions required sustained mental effort: stimulus-response mappings depended on different combinations of multiple features. In the other task the instructions required very little mental effort: responses depended on a single feature. The idea was that the difficult task would demand attention and integration of information, whereas the easy task would rely only on automatic visuo-motor skills.

Unbeknownst to the participants, the tasks had been manipulated such that color always predicted the correct response. The straight-forward hypothesis is that the cognitive system should automatically pick-up on this feature and that performance should be enhanced by the exertion of mental effort. However, this is not what we observed. Counter intuitively, the predictive information impaired performance when participants were exerting control.

In other words, the additional mental effort interfered with participants’ perfectly adequate automatic visuo-motor skills. These findings show that less can sometimes be more (in terms of cognitive control), especially if the environment provides sufficient information for the cognitive system to “autopilot” behavior based on automatic processes alone. Apparently, people can overthink their highly automatic skills by exerting mental effort.

Practically, there are quite a few situations when we might potentially encounter this effect in daily life. For example, when driving a car you have no difficulty reacting to situations until you suddenly have think about how to shift gears. You are then switching from automatic pilot to controlled processing. The problem is that the cognitive control system can only handle one thing at a time. Your extra mental effort disrupts your more than adequate concatenated sequence of automatic motor actions. The automatic system is put on hold, as it were. This effect could be indeed be general: When you exercise cognitive mental control over a complex motor sequence that you are already very proficient at performing, such as playing the piano or touch-typing, a break in the chain of automatic actions may be detrimental. This may be particularly relevant for professional athletes.

This is not say that exerting cognitive control is not useful! In fact, it is essential to exert cognitive control up until the point that you have mastered something and your skills become automatic. Only then should you try to ‘let go’ and perform a task on “autopilot”.


Bocanegra, B. R., & Hommel, B. (2014). When Cognitive Control Is Not Adaptive. Psychological Science, 25, 1249-1255.

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