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Pupil Constriction Causes Activity in the Human Retina and Visual System
Sebastiaan Mathôt1, Olaf Dimigen1, Hakan Karsilar1
1Department of Psychology, University of Groningen, Groningen, the Netherlands.
Psychophysiology
|July 23, 2026
Summary
Pupil constriction, not just light, triggers retinal and brain activity. This discovery reveals a new mechanism in visual processing, independent of external visual stimuli.
Area of Science:
- Neuroscience
- Visual Perception
- Ophthalmology
Background:
- Pupil size regulates light entry, influencing early visual processing.
- The precise impact of pupil responses on visual processing remains unclear.
- Existing research has not fully explored non-visual stimulation-driven neural activity.
Purpose of the Study:
- To investigate whether pupil constriction itself generates neural activity in the human visual system.
- To differentiate neural responses locked to visual stimuli versus those locked to pupil responses.
- To understand the implications of pupil-driven activity for visual perception, such as brightness constancy.
Main Methods:
- Recorded pupil size, electroretinogram (retinal activity), and electroencephalogram (brain activity) in 119 healthy participants.
- Presented brief visual stimuli (light increments/decrements) to participants.
- Analyzed trial-to-trial variability in pupil constriction latency to identify stimulus-independent responses.
Main Results:
- Identified a novel retinal response (electroretinogram) and visual cortex response (electroencephalogram) locked to pupil constriction latency, not visual stimulation.
- This constriction-locked activity occurs independently of the initial visual stimulus.
- Findings suggest pupil constriction itself induces neural activity in the retina and visual cortex.
Conclusions:
- Pupil constriction elicits neural activity in the human retina and visual system, separate from visual stimulation.
- This suggests a previously unrecognized pathway where motor output (pupil constriction) influences sensory processing.
- Further research is needed to understand how the visual system achieves brightness constancy despite this pupil-induced neural activity.
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