Wednesday, 9 September 2015

Mental effort is contagious

If you're about to dive into a piece of work that requires intense mental focus, you might find it helps to sit next to someone else who is concentrating hard. According to an ingenious new study published in Psychonomic Bulletin and Review, mental exertion is contagious: if a person near you is straining their synapses in mental effort, their mindset will automatically intensify your own concentration levels.

Psychologists have known since at least the 1960s that the presence of other people affects our own performance in predictable ways. For example, the 1965 Social Facilitation Theory describes how the presence of other people makes it easier to perform well-rehearsed, automatic behaviours. Yet company can also be distracting and make it more difficult to perform behaviours that require mental control.

Kobe Desender at Vrije Universiteit in Belgium and his colleagues wanted to build on these findings by testing whether it makes a difference to our performance what other people present are doing – and specifically, if someone else is using a lot of mental effort, does that affect how much mental effort we exert ourselves?

Thirty-eight participants (20 women; average age 22) performed a version of what's known as the "Simon task" in pairs. Coloured squares appeared on either the left or right-hand side of a computer screen. When two of the four possible colours of square appeared, the person sat to the left of the screen was required to press the 'd' keyboard key as fast as possible with their left hand. When either of the two other possible coloured squares appeared, the person on the right was required to press the 'k' key as fast as possible with their right hand. Superior performance is revealed through faster responding and fewer errors. Although the task was performed in pairs in this way, there was no need or possibility for collaboration between partners, nor was there any competition.

Image from Desender et al, 2015. (A) shows the set-up for the first experiment, (B) for the second experiment.
An important thing to understand about this task is that it was easier for participants to respond to a target square (i.e. one that was a colour that they had been instructed to respond to) when it appeared on the same side that they were sitting, and that was therefore also the same side as the hand they were using to respond – that is, when the target and response were congruent. Also, the higher the proportion of congruent trials that a participant was subjected to, the easier the task would become, because they could switch to a more automatic mode of responding.

The researchers manipulated task difficultly individually for each person in a pair by varying their proportion of congruent versus incongruent trials. The issue of stimulus-repsonse congruence also provided a ready indicator of a person's concentration levels. If a person was trying really hard, their performance would be less affected by whether their target squares were congruent or not.

Desender and his team were especially interested in those instances when they made the task super difficult for one participant (he or she had only 10 per cent congruent trials), but they kept the difficulty medium for the other participant (they had a 50/50 mix of congruent and incongruent trials). In this situation, the participant in the difficult version was required to use maximum mental effort to succeed. The intriguing finding is that this mental effort influenced their partner. A person playing alongside someone who was forced to concentrate really hard was themselves less influenced by their own targets' congruency – a sure sign that they too were trying harder than normal. Somehow one person's hidden mental effort seemed to influence the other.

Further analysis confirmed that this effect was not caused simply by one player mimicking the other's response speed. Nor was it that the participants were influenced by looking at their partner's ratio of congruent and incongruent trials and seeing that their task was more difficult. The researchers ruled out this possibility in a follow-up study in which each player had their own display, and a piece of cardboard stopped them from being able to see their partner's squares (see figure B above).

The researchers don't know what led one player's levels of mental effort to contaminate their partner, but they speculate that perhaps it had to do with body posture. Maybe the person forced to concentrate extra hard adopted a more tense body posture and this sign of mental effort automatically influenced their partner to also concentrate extra hard. However, they added that a "more radical hypothesis should also be considered, such as the possibility that effort exertion is influenced by a difference in scent of someone else exerting high or low effort."


Desender, K., Beurms, S., & Van den Bussche, E. (2015). Is mental effort exertion contagious? Psychonomic Bulletin & Review DOI: 10.3758/s13423-015-0923-3

--further reading--
Social flow - how doing it together beats doing it alone
Faster, Higher, Stronger: The Psychology of Competition
Guilt is catching
The smell of fear more powerful than previously realised

Post written by Christian Jarrett (@psych_writer) for the BPS Research Digest.

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