The perceptual consequences and neurophysiology of eye blinks

Abstract

A hand passing in front of a camera produces a large and obvious disruption of a video. Yet the closure of the eyelid during a blink, which lasts for hundreds of milliseconds and occurs thousands of times per day, typically goes unnoticed. What are the neural mechanisms that mediate our uninterrupted visual experience despite frequent occlusion of the eyes? Here, we review the existing literature on the neurophysiology, perceptual consequences, and behavioral dynamics of blinks. We begin by detailing the kinematics of the eyelid that define a blink. We next discuss the ways in which blinks alter visual function by occluding the pupil, decreasing visual sensitivity, and moving the eyes. Then, to anchor our understanding, we review the similarities between blinks and other actions that lead to reductions in visual sensitivity, such as saccadic eye movements. The similarity between these two actions has led to suggestions that they share a common neural substrate. We consider the extent of overlap in their neural circuits and go on to explain how recent findings regarding saccade suppression cast doubt on the strong version of the shared mechanism hypothesis. We also evaluate alternative explanations of how blink-related processes modulate neural activity to maintain visual stability: a reverberating corticothalamic loop to maintain information in the face of lid closure; and a suppression of visual transients related to lid closure. Next, we survey the many areas throughout the brain that contribute to the execution of, regulation of, or response to blinks. Regardless of the underlying mechanisms, blinks drastically attenuate our visual abilities, yet these perturbations fail to reach awareness. We conclude by outlining opportunities for future work to better understand how the brain maintains visual perception in the face of eye blinks. Future work will likely benefit from incorporating theories of perceptual stability, neurophysiology, and novel behavior paradigms to address issues central to our understanding of natural visual behavior and for the clinical rehabilitation of active vision.

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“…These blinks have several suggested causes including; relief from the accommodation required to visualize the target, protecting the eyes from the item when bringing the hand to the mouth, switching from visual to somatosensory guidance, or reflecting a central network change such as alternating between an attention network and the default network (Ang and Maus, 2020;Brych and Handle, 2020;Jaschinski et al, 1996;Nakano et al, 2013;Willett et al, 2023). Here we made a new observation of the relation between blinks and gaze that has a bearing on these suggestions.…”

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“…Blinking serves many purposes, including hydration of the cornea and protection of the eye from external damage. Spontaneous blinks are the most common, and occur unconsciously, approximately 15 times a second, and generally in the absence of inciting stimuli [ 43 ]. Humans blink spontaneously more frequently than required to maintain eye lubrication, and spontaneous blinks are linked to cognitive processes and attention [ 44 ].…”

“…Humans blink spontaneously more frequently than required to maintain eye lubrication, and spontaneous blinks are linked to cognitive processes and attention [ 44 ]. Similar mechanisms and muscles mediate the mechanical output of all types of blinks and are controlled by brainstem structures [ 43 ]. While reflexive blinks are maintained as a brainstem circuit between the fifth and seventh cranial nerves in response to perturbation of the eye, the timing of spontaneous blinks involves a somatosensory network in the upper cortical structures.…”

“…While reflexive blinks are maintained as a brainstem circuit between the fifth and seventh cranial nerves in response to perturbation of the eye, the timing of spontaneous blinks involves a somatosensory network in the upper cortical structures. Visual cortical areas are also intricately involved in mediating uninterrupted vision, despite the occlusion of the eye to visual stimuli during a blink [ 43 ]. The frequency of eye blinks is the most common blink measurement in the context of cognitive state [ 6 ].…”

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“…Blinks are often linked to cognitive and neurological processes controlling eye movements [ 29 , 30 ]. The coordination of blinks with saccadic movements is well-documented.…”