The hot-headed “macho man”, who acts first and thinks later, has long been popular in movies.  Now there’s psychological evidence to support it. A new study in the Psychological Science finds that a short-term rise in testosterone – as might occur when in the presence of an attractive potential mate, or during competition – shifts the way men think, encouraging them to rely on quick, intuitive, and generally less accurate, judgements, rather than engaging in careful, more deliberate thought.

In the biggest investigation of the effects of testosterone on human behaviour to date, a team from Caltech, the University of Pennsylvania, Western University and the ZRT Laboratory in Oregon, recruited 243 men, mostly college students. The men rubbed a gel that they were told either contained testosterone or was a placebo over their shoulders, upper arms and chest. Four-and-a-half hours later – enough time for their testosterone levels to peak – they embarked on a series of tests (saliva samples taken from the men through the study confirmed that testosterone levels were indeed higher in the group that applied the gel that contained testosterone).

The most critical test, in terms of the study aims, was the three-item Cognitive Reflection Test, which evaluates a person’s ability to override quick and intuitive, but likely incorrect, judgements through deliberate, careful thought. The volunteers were told that they’d be paid $1 for each correct answer, with a bonus of $2 for three correct answers, and they could take as long as they liked.

An example from the test: A bat and a ball cost $1.10 in total. The bat costs $1.00 more than the ball. How much does the ball cost? 

Earlier work has found that, when presented with this question, most people go with their first thought, and answer, incorrectly, 10 cents – even though it is straightforward to check the answer, which would show that 10 cents is wrong. With a little deliberation, it’s not too difficult for most people to work out the right answer*.

The researchers found that the men who’d received testosterone performed significantly worse on this test. Overall, they came up with 20 per cent fewer correct answers than the men who’d received the placebo. What’s more, when volunteers who’d received testosterone gave correct answers, they tended to do this more slowly than the volunteers who’d got the placebo. While the team didn’t measure individual volunteers’ testosterone levels, based on previous work on the dose used (100 mg of topical 1 per cent testosterone), they were probably at around the level that young men experience during real-world competition, the researchers say.

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