Broadening of attention dilates the pupil

Kolnes, Martin; Uusberg, Andero; Nieuwenhuis, Sander · 2024 · Crossref

DOI: 10.3758/s13414-023-02793-3

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Summary

This study investigates the relationship between the breadth of visual attention and pupil size, addressing inconclusive evidence suggesting that pupils dilate when attention broadens. The authors hypothesized that pupil size scales with attentional breadth, potentially optimizing early visual processing by trading off visual acuity for sensitivity. Crucially, the study aimed to replicate prior findings while controlling for confounding variables such as mental effort and eye vergence movements, which can independently influence pupil dilation. Additionally, the researchers tested whether pupil dilation functionally mediates the behavioral effects of attentional breadth on visual search performance. To test these hypotheses, 22 participants completed a dual-task paradigm combining a shape-discrimination task to induce attentional breadth and a visual search task to assess behavioral outcomes. In the induction phase, participants viewed either a small Landolt circle (radius 0.7°) to induce narrow attention or a large circle (radius 7°) to induce broad attention, remembering the gap location. This was immediately followed by a visual search task where participants detected a tilted ellipse among distractors at varying distances (1°, 3°, or 6°) from the screen center. Pupil size was recorded at 120 Hz. Data analysis employed Generalized Additive Mixed Models (GAMMs) to model pupil dynamics while statistically controlling for gaze location and eye vergence. Behavioral performance was analyzed using Drift Diffusion Modeling (DDM) to quantify decision-making efficiency, and causal mediation analysis was used to test if pupil size mediated the effect of attentional breadth on reaction times. The results confirmed that pupils were significantly more dilated during the broad-breadth-of-attention condition compared to the narrow condition, even after controlling for confounds. Behavioral analysis via DDM showed that the manipulation successfully altered attentional scope: the decline in processing efficiency (drift rate) as target distance increased was milder in the broad-attention condition than in the narrow condition. However, the mediation analysis revealed that pupil size did not mediate the effect of attentional breadth on visual search performance. This indicates that while pupil dilation correlates with the broadening of attention, it does not causally drive the associated changes in perceptual performance. The study concludes that pupil dilation is a robust correlate of broadened attentional focus, supporting the hypothesis that these two mechanisms co-occur. However, the lack of mediation suggests the relationship is likely correlational rather than functional; pupil size may reflect the activity of underlying neural systems, such as the noradrenergic system, that regulate both attention and pupillary responses, rather than serving as the mechanism through which attentional breadth affects perception. These findings clarify the functional role of pupil dynamics in attention and highlight the need for further research to disentangle the neural drivers of these concurrent physiological and cognitive states.

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