The effects of cognitive abilities and task demands on tonic and phasic pupil sizes

•Tonic and phasic pupil responses were measured prior and during multiple object tracking (MOT).•Individual differences in general cognitive abilities did not relate to either the tonic or phasic pupil sizes.•High MOT performers had larger phasic pupil responses than low performers only during the highest workload conditions.•Individual differences in task-evoked pupil sizes are related to state-specific factors and not to general cognitive abilities. Previous studies on individual differences in pupil size of healthy individuals and their relation to performance have been inconclusive. Using a novel approach, we tested the effect of general cognitive abilities and level of task performance on pretrial baseline and task-evoked pupil (TEP) sizes (N = 116) while we manipulated the level of task demands using a multiple object tracking task. Results did not reveal an effect of general cognitive abilities, estimated by working memory capacity and gF scores, on either baseline or TEP sizes. In contrast, we found an interaction in TEP sizes between level of overall MOT performance and task demands. We propose that individual differences in TEP sizes are related to state-specific level of task performance and task demands, probably in combination with other factors like age, personality traits, and state-specific level of motivation and arousal. We also suggest methodological confounds that may cause the previous inconclusive findings.