Is pupil size an index of insight, analysis, and/or uncertainty? An extended replication study of problem-solving to take account of combined strategies, timing and accuracy.

Research indicates that greater pupil dilation distinguishes insight from analytic problem solving, but it remains unclear how time-to-solution and the potential use of combined strategies influence this finding. To address this, we asked participants in the current study to categorise each trial as one of three strategies, and we examined the interaction between strategy type, accuracy and time-to-solution to predict pupil dilation. English-speaking students (n = 38) were asked to solve 120 compound word association problems, while pupil dilation was recorded. Subsequently, participants were asked to report which of the three problem-solving strategies (analytic, insight, combined) they had used to find each solution, without being if their answers were correct. A Bayesian linear mixed model analysis revealed an interaction between time-to-solution and strategy. More specifically, pupil dilation indexed an insight strategy for early solutions, but indicated an analytic strategy for late solutions, with combined strategies falling in between. In addition, correct trials were associated with greater pupil dilation. We conclude that, even within the same task, pupil dilation may separately indicate (1) the extended mental effort of problem analysis, (2) the immediate onset of insight, and (3) the feeling of uncertainty experienced when a correct answer is unvalidated by feedback. Future research should rule out other explanations such as whether pupil dilation is an index of change in affect, and test hypothetical closed-loop models of problem-solving directly through individualised model fitting.