Tonic pupil size and its variability are associated with fluid intelligence in adolescents aged 11-14 years.

Tonic pupil size and its variability are sensitive to cognitive abilities (such as fluid intelligence [Gf]) among individuals. The present study aimed to examine this relationship in a new sample set (i.e., adolescents aged 11-14 years) with several important factors considered. We conducted two task-free tasks (the blank-screen viewing task and the scene viewing task) to measure tonic pupil size and its variability in 11-14-year-old adolescents with different Gf levels and preliminarily tested the role of task type and stimuli's luminance on this relationship. The results found that high-Gf adolescents showed smaller tonic pupil size in both tasks but showed larger variability of tonic pupil size in the blank-screen viewing task. Task type and stimuli's luminance could influence tonic pupil size and its variability in different ways. Cognitive and underlying neural mechanisms of these results are discussed to provide an explanation and suggestions for future studies.