Test-retest reliability and behavioural correlates of pupil responses in an n-back task

The measurement of pupil size changes is a promising method to investigate the neural correlates of information processing. Whereas a long line of research demonstrates that pupil responses are sensitive to specific characteristics of information processing (e.g. mental effort, attentional allocation, surprise), an emerging line of research investigates whether individual differences in pupil size measures are predictive of individual differences in specific aspects of information processing. Our study contributes to this stream of resarch (1) by investigating whether pupillary changes during performing a demanding working memory task (the n-back paradigm) are correlated with task performance, and (2) by testing whether these pupil responses demonstrate temporal stability over a period of multiple weeks (test-retest reliability). Our results show that pupil responses were correlated with task performance only on the second session, though pupil size measures recorded on the two sessions show moderate correlations with each other. Whereas the failure to demonstrate significant correlations between behavioural performance and pupil size measures might be caused by low statistical power inherent in our design, the demonstrated between-subjects correlations suggest that pupil responses might be temporally stable also in such cases when the pupil response itself is not predictive of task performance. Future studies are needed to inspect the test-retest reliability of pupillary measures to ensure that the between-sessions correlations among participants are caused by individual differences in information processing, and not by other methodological factors (e.g. participant-specific, systematic measurement noise).