Working, studying, and doing sudokus or crossword puzzles are all examples of tasks that require a considerable mental effort. When and why do we agree to expend cognitive effort? What individual circumstances and characteristics influence this decision? These are the questions that Ross Otto, a professor in the Department of Psychology at McGill University, is trying to answer. Specifically, he is interested in the calculation of relative costs (such as time) and benefits (such as financial benefits) that informs each decision on whether or not to make a mental effort.

He and his collaborators are using cutting-edge behavioural experiments based on mathematical models combined with psychological measurements, such as pupillary responses. For instance, they ask participants to count backwards using a fixed rule of varying cognitive complexity, while the researchers analyze the cognitive effort expended. The introduction of some form of reward – monetary, for example – then allows them to assess the differences in individual responses to the cost-benefit trade-off.

The researchers observed that the perceived cost of even a subtle variation in the mental effort required is greater for some activities that for others. Moreover, it appears that individuals are very sensitive to the notion of ‘marginal cost’ and internalize it in their decision making. That being said, some people are more motivated to invest effort, either because they are offered a reward or because they are intrinsically motivated. These findings are of prime importance for understanding the choices that many people are regularly asked to make, such as those concerning their health; vaccination against COVID-19 is a good example.