Reliability and correlates of intra-individual variability in the oculomotor system

Perquin, Marlou Nadine; Bompas, Aline · 2019 · Crossref

DOI: 10.16910/jemr.12.6.11

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Summary

This study investigates the intra-individual reliability of oculomotor measures and their potential correlation with self-assessed psychological traits, specifically ADHD tendencies, mind wandering, and impulsivity. While previous research has linked oculomotor variability to ADHD at the group level, it remains unclear whether these measures constitute stable individual traits suitable for use as biomarkers. The authors address this gap by examining the repeatability (consistency over time) and generalization (consistency across conditions) of microsaccade rate, blink rate, pupil size, and gaze position variability in healthy participants. The research combined data from three experiments involving over 100 healthy participants. Experiment 1 assessed reliability over time by measuring oculomotor features before and after a behavioral task. Experiment 2 extended this by testing reliability across different days. Experiment 3 examined generalization across three distinct resting-state conditions: fixation with instruction, no fixation with instruction, and no fixation with no instruction. Eye movements were recorded using eye-tracking technology (Eyelink 1000) during resting-state paradigms where participants fixated on a static dot or blank screen. Participants also completed validated questionnaires: the Adult ADHD Self-Report Scale (ASRS-v1.1), the Daydreaming Frequency Scale (DFS), and the UPPS-P Impulsive Behaviour Scale. Statistical analyses employed Bayesian methods to evaluate correlations and reliability, with oculomotor measures log-transformed to address skewness. The results demonstrated that most oculomotor measures exhibited good intra-individual reliability. In Experiment 1, all measures showed high positive correlations and extreme Bayes Factors between the pre-task and post-task sessions, indicating strong consistency over time. Experiments 2 and 3 further confirmed that blink rate, pupil size, and microsaccade rate remained reliable across different days and experimental conditions. However, gaze variability, particularly in the horizontal dimension, showed lower reliability. Crucially, the study found no significant correlations between any of the oculomotor measures and self-assessed scores for ADHD tendencies, mind wandering, or impulsivity. The Bayesian analyses provided evidence in favor of the null hypothesis for these associations, suggesting that these oculomotor features do not predict these specific psychological traits in healthy individuals. The significance of these findings lies in establishing that while oculomotor variability is a stable individual trait with high test-retest reliability, it does not serve as a valid biomarker for self-assessed ADHD, mind wandering, or impulsivity in healthy populations. The authors conclude that the lack of correlation in previous studies may have been due to insufficient statistical power or reliability issues, but their robust data suggests these measures simply do not correlate with these traits. The study highlights the necessity of establishing intra-individual reliability before investigating between-subject differences and cautions against interpreting oculomotor variability as a direct indicator of these specific cognitive or behavioral tendencies.

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