Chapter 3 Eye and eyelid movements during blinking: an eye blink centre?

The perceptual consequences and neurophysiology of eye blinks

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.

Electrooculograms for Human-Computer Interaction: A Review

Eye movements generate electric signals, which a user can employ to control his/her environment and communicate with others. This paper presents a review of previous studies on such electric signals, that is, electrooculograms (EOGs), from the perspective of human–computer interaction (HCI). EOGs represent one of the easiest means to estimate eye movements by using a low-cost device, and have been often considered and utilized for HCI applications, such as to facilitate typing on a virtual keyboard, moving a mouse, or controlling a wheelchair. The objective of this study is to summarize the experimental procedures of previous studies and provide a guide for researchers interested in this field. In this work the basic characteristics of EOGs, associated measurements, and signal processing and pattern recognition algorithms are briefly reviewed, and various applications reported in the existing literature are listed. It is expected that EOGs will be a useful source of communication in virtual reality environments, and can act as a valuable communication tools for people with amyotrophic lateral sclerosis.

Electrooculogram and submandibular montage to distinguish different eye, eyelid, and tongue movements in electroencephalographic studies

OBJECTIVE

We propose an electrooculogram and submandibular montage that helps to discriminate eye/eyelid/tongue movements and to differentiate them from epileptiform activity or slowing on electroencephalography (EEG).

METHODS

We analyzed different eye/eyelid and tongue movements in 6 and 4 patients, respectively. Six peri-orbitally and one submandibular electrodes were placed. We referred these electrodes to an indifferent reference (Cz/Pz) and we recorded eye/eyelid and tongue movements simultaneously with the 10-20 system EEG. Additionally, we analyzed 2 seizures with the electrooculogram montage.

RESULTS

The electrooculogram deflections always showed an opposite phase direction when eye/eyelid movements occurred. Conversely, epileptiform activity produced deflections in the same phase direction in all electrooculogram electrodes. The electrooculogram montage was able to distinguish eye ictal semiology. Vertical tongue movements showed opposite phase deflections between the submandibular and the inferior ocular electrodes. Horizontal tongue movements revealed opposite phase reversal deflections between both inferior ocular electrodes.

CONCLUSIONS

The proposed montage accurately defines different eye/eyelid and tongue movements from brainwave activity. Additionally, it is useful to differentiate eye/eyelid movements from epileptiform activity and to characterize ictal ocular semiology, which can help localize or lateralize the epileptogenic zone.

SIGNIFICANCE

We propose this new montage to provide added value to prolonged video-EEG studies.

Blinks and saccades as indicators of fatigue in sleepiness warnings: looking tired?

The present study examines changes in a variety of oculomotoric variables as a function of increasing sleepiness in 129 participants, who have been passed through a broad range of subjective alertness. Up to now, spontaneous eye blinks are the most promising biosignal for in-car sleepiness warnings. Reviewing the current literature on eye movements and fatigue, experimental data are provided including additional indicative oculomotoric parameters; inter-individual differences in the experiments were also assessed. Here, self-rated alertness decreased over six steps on average and proved itself a reliable measurement. Regarding oculomotoric parameters, blink duration, delay of lid reopening, blink interval and standardised lid closure speed were identified as the best indicators of subjective as well as objective sleepiness. Saccadic parameters and fixation durations also showed specific changes with increasing sleepiness. Substantial inter-individual differences in all of these variables were illustrated. Oculomotoric parameters were linked to three different components of sleepiness while driving: a) deactivation; b) decreasing attention, resulting in disinhibition of spontaneous blinks and reflexive saccades; c) increasing attempts of self-activation. Finally, implications for the development of drowsiness detection devices were discussed.

Are locus coeruleus neurons involved in blinking?

To investigate the involvement of the noradrenergic locus coeruleus (LC) in the reflex blink circuit, c-Fos and neuronal tracer experiments were performed in the rat. LC neurons involved in reflex blink were localized by analyzing c-Fos protein expression after electrical stimulation of the supraorbital nerve. Subsequently, neuronal tracers were injected in two different nuclei which are part of the reflex blink circuit. Anterograde tracer experiments in the sensory trigeminal complex (STC) explored the trigemino-coerulear connection; retrograde tracer experiments in the latero-caudal portion of the superior colliculus (SC) established coerulear-collicular connections. The combination of retrograde tracer injections into the latero-caudal SC portion combined with electrical stimulation of the supraorbital nerve identified c-Fos positive LC neurons that project to the latero-caudal SC. Our results revealed the existence of a STC-LC-SC loop.