Mentalizing and heuristics as distinct cognitive strategies in human teaching.
Teaching is a foundational social behaviour that can result from mentally effortful reasoning or cognitively frugal heuristics. When do people use these strategies to teach? Here we investigated this using behavioural experiments and computational modelling with adult participants recruited via Prolific. Experiment 1 (N = 100) revealed robust individual differences: some participants taught by reasoning about a learner's knowledge, consistent with an optimal Bayesian pedagogy model, while others relied on simple heuristics that do not require mentalizing. In two preregistered follow-up experiments, we found that people persist in using heuristics even when they are no longer effective (experiment 2, N = 253, P < 0.001, rank-biserial r = 0.287, 95% confidence interval 0.149-0.419) but that this tendency is pre-empted when inference about a learner's knowledge is scaffolded using an auxiliary task (experiment 3, N = 759, P < 0.001, partial η p 2 = 0 . 107 , 95% confidence interval 0.068-0.148). These results demonstrate sophisticated arbitration between planning and heuristics during teaching and elucidate the more general mechanisms involved in adapting mental effort during social interactions.