CNS*2026 Halifax

Introduction
Traditionally, the pupillary light response is viewed as a global reflex stabilizing retinal illumination by integrating luminance across the visual field [1]. However, recent work suggests pupil responses are also modulated by spatial mechanisms linked to attention and eye movement planning. When global luminance is held constant, directing attention to brighter regions produces stronger constriction, indicating location-specific luminance weighting [2]. Moreover, the pupil can begin adjusting to upcoming saccade target luminance before gaze shifts, suggesting anticipatory modulation linked to presaccadic attention [3]. Together, these findings suggest pupil dynamics reflect both global and gaze-dependent local luminance signals.


Methods
51 participants (ages 20-25) were recorded with an EyeLink-1000 eye-tracker while freely viewing 10 naturalistic movies. First, luminance was extracted at the pixel level frame-by-frame using a photometric calibration. Analysis 1: gaze-contingent retinal luminance was mapped onto a 1°×1° spatial grid and regularized regression was used to estimate spatial luminance sensitivity of the pupil across the visual field. Analysis 2: intersaccadic intervals (ISI) between saccades were identified and linear mixed-effects models tested whether late-ISI pupil diameter predicted upcoming saccade goal luminance, controlling for current fixation, opposite-direction (control location), and global luminance.


Results

Discussion
These findings advance understanding of how pupil dynamics encode spatial and temporal visual information during natural viewing. Central weighting (Analysis 1) likely reflects attentional allocation. The anticipatory effect at upcoming saccade targets (Analysis 2) suggests presaccadic attention modulates pupillary responses before gaze arrival, consistent with oculomotor structures such as the superior colliculus and frontal eye fields influencing pupil control [4]. Limitations include use of instantaneous pupil measurements without accounting for pupillomotor delay (~200-300ms) in analysis 2. Ongoing work aims to incorporate temporal lags in analysis 2 and test generalizability across diverse tasks.


References

1. Watson, A. B., & Yellott, J. I. (2012). A unified formula for light-adapted pupil size. Journal of vision, 12(10), 12. https://doi.org/10.1167/12.10.12
2. Binda, P., & Murray, S. O. (2015). Spatial attention increases the pupillary response to light changes. Journal of vision, 15(2), 1. https://doi.org/10.1167/15.2.1
3. Mathôt, S., van der Linden, L., Grainger, J., & Vitu, F. (2015). The pupillary light response reflects eye-movement preparation. Journal of experimental psychology. Human perception and performance, 41(1), 28–35. https://doi.org/10.1037/a0038653
4. C. Wang, & D.P. Munoz, Neural basis of location-specific pupil luminance modulation, Proc. Natl. Acad. Sci. 115 (41), 10446-10451, https://doi.org/10.1073/pnas.1809668115

Acknowledgement
The research was undertaken thanks in part to funding from the Connected Minds Program, supported by Canada First Research Excellence Fund, Grant #CFREF-2022-00010, and the Natural Sciences and Engineering Research Council of Canada (NSERC).