If you’re headed into some important meeting, you might down a cup or two of coffee without thinking much of it, hoping the caffeine will provide your brain with an extra boost. But in his new book on personality science, psychologist Brian Little suggests that for introverts, this strategy may backfire.

Here’s what Little writes in Me, Myself, and Us: The Science of Personality and the Art of Well-Being, which was just released last week:

After ingesting about two cups of coffee, extraverts carry out tasks more efficiently, whereas introverts perform less well. This deficit is magnified if the task they are engaging in is quantitative and if it is done under time pressure. For an introvert, an innocent couple cups of coffee before a meeting may prove challenging, particularly if the purpose of the meeting is a rapid-fire discussion of budget projections, data analysis, or similar quantitative concerns. In the same meeting, an extraverted colleague is likely to benefit from a caffeine kick.

Intriguing. Science of Us contacted Little, a lecturer at Cambridge University, to find out more.

Why does coffee seem to have this effect on introverts?

This isn’t my own research, but it’s based on the theory of extraversion by Hans Eysenck and research by William Revelle of Northwestern University. It’s the idea that introverts and extraverts differ in the level of neocortical arousal in the brain — in other words, how alert or responsive you are to your environment. According to this theory, introverts are over the optimal level — that is, more easily stimulated — and extraverts under the optimal level.

It’s more complex than that, but this is a useful model because it allows us to make some predictions. This suggests that performance will be compromised for introverts if they are exposed to stimulating situations, or if they ingest a stimulant (such as caffeine),which pushes them even further away from the optimal level.

So when should introverts have their coffee, then?

Later in the day would be better; at any rate, they should try not to have caffeine right before something like an important meeting, as I say in the book.

Are there other foods or drinks that may have a similar effect on introverts?

Anything that is a central nervous system stimulant (including recreational stimulants). Being in a noisy, overloading place will create a similar effect.