Eye Blink Rates and Eyelid Twitches as a Non-Invasive Measure of Stress in the Domestic Horse.
ABSTRACT: Physiological changes provide indices of stress responses, however, behavioural measures may be easier to determine. Spontaneous eye blink rate has potential as a non-invasive indicator of stress. Eyelid movements, along with heart rate (HR) and behaviour, from 33 horses were evaluated over four treatments: (1) control-horse in its normal paddock environment; (2) feed restriction-feed was withheld at regular feeding time; (3) separation-horse was removed from visual contact with their paddock mates; and (4) startle test-a ball was suddenly thrown on the ground in front of the horse. HR data was collected every five s throughout each three min test. Eyelid movements and behaviours were retrospectively determined from video recordings. A generalized linear mixed model (GLIMMIX) procedure with Sidak's multiple comparisons of least squares means demonstrated that both full blinks (16 ± 12b vs. 15 ± 15b vs. 13 ± 11b vs. 26 ± 20a full blinks/3 min ± SEM; a,b differ p < 0.006) and half blinks (34 ± 15ab vs. 27 ± 14bc vs. 25 ± 13c vs. 42 ± 22a half blinks/3 min ± SEM; a,b,c differ p < 0.0001) decreased during feed restriction, separation and the startle test compared to the control, respectively. Eyelid twitches occurred more frequently in feed restriction (p < 0.0001) along with an increased HR (p < 0.0001). This study demonstrates that spontaneous blink rate decreases while eyelid twitches increase when the horse experiences a stressful situation.
Project description:Purpose:To develop an eye model with a physiological blink mechanism. Methods:All parts of the eye model were designed using computer-aided design software. The eyelid consisted of a unique 3D printed structure containing teeth to physically secure a flexible membrane. Both the eyeball and eyelid membrane were synthesized using polyvinyl alcohol (PVA). Four molecular weights of PVA (89-98, 85-124, 130, and 146-186 kDa) were tested at a range of concentrations between 5% and 30% weight/volume. The wettability and water content of these materials were compared with the bovine cornea and sclera. The model was connected to a microfluidic pump, which delivers artificial tear solution (ATS) to the eyelid. A corneal topographer was used to evaluate the tear break-up and tear film regeneration. Results:The eyelid flexes and slides across the eyeball during each blink, which ensures direct contact between the two surfaces. When loaded with an ATS, this mechanism evenly spreads the solution over the eyeball to generate an artificial tear film. The artificial tear film in this eye model had a tear break-up time (TBUT) of 5.13 ± 0.09 seconds at 1.4 μL/min flow rate, 6 blinks/min, and <25% humidity. Conclusions:This model simulates a physiological blink actuation and an artificial tear film layer. Future studies will examine variations in flow rates and ATS composition to simulate clinical values of TBUT. Translational Relevance:The eye model could be used to study in vitro TBUT, tear deposition, and simple drug delivery.
Project description:It is known that TMS can induce blinking, but it is unknown to what extent and at what time TMS-induced blinking can cover the pupil. We applied single-pulse TMS with a leftward and rightward monophasic current through a round coil over the occipital pole in 8 healthy subjects, using high-speed video to monitor left or right eye with a spatial resolution of 0.1 mm and a temporal resolution of 2 ms. We plotted eyelid position relative to upper and lower pupil borders as a function of time after TMS for each subject and current direction. We found 2 blinks in every subject, an isolated late blink with one current direction and a superimposed early and late blink with the other current direction, in accordance with our previously reported association between a leftward and rightward lower coil rim current and an early blink in right and left eye, respectively. Blink extent varied, but 4 subjects showed total pupil covering with both current directions. Blink timing varied, but pupil covering was initiated as early as 32 ms after TMS and pupil uncovering was completed as late as 200 ms after TMS. We found no saccades. We conclude that TMS can cause an important optical disruption of visual perception.
Project description:IMPORTANCE Facial paralysis remains one of the most challenging conditions to effectively manage, often causing life-altering deficits in both function and appearance. Facial rehabilitation via pacing and robotic technology has great yet unmet potential. A critical first step toward reanimating symmetrical facial movement in cases of unilateral paralysis is the detection of healthy movement to use as a trigger for stimulated movement. OBJECTIVE To test a blink detection system that can be attached to standard eyeglasses and used as part of a closed-loop facial pacing system. DESIGN, SETTING, AND PARTICIPANTS Standard safety glasses were equipped with an infrared (IR) emitter-detector unit, oriented horizontally across the palpebral fissure, creating a monitored IR beam that became interrupted when the eyelids closed, and were tested in 24 healthy volunteers from a tertiary care facial nerve center community. MAIN OUTCOMES AND MEASURES Video-quantified blinking was compared with both IR sensor signal magnitude and rate of change in healthy participants with their gaze in repose, while they shifted their gaze from central to far-peripheral positions, and during the production of particular facial expressions. RESULTS Blink detection based on signal magnitude achieved 100% sensitivity in forward gaze but generated false detections on downward gaze. Calculations of peak rate of signal change (first derivative) typically distinguished blinks from gaze-related eyelid movements. During forward gaze, 87% of detected blink events were true positives, 11% were false positives, and 2% were false negatives. Of the 11% false positives, 6% were associated with partial eyelid closures. During gaze changes, false blink detection occurred 6% of the time during lateral eye movements, 10% of the time during upward movements, 47% of the time during downward movements, and 6% of the time for movements from an upward or downward gaze back to the primary gaze. Facial expressions disrupted sensor output if they caused substantial squinting or shifted the glasses. CONCLUSIONS AND RELEVANCE Our blink detection system provides a reliable, noninvasive indication of eyelid closure using an invisible light beam passing in front of the eye. Future versions will aim to mitigate detection errors by using multiple IR emitter-detector units mounted on glasses, and alternative frame designs may reduce shifting of the sensors relative to the eye during facial movements.
Project description:To detect and quantify eye blinks during 24-hour intraocular pressure (IOP) monitoring with a contact lens sensor (CLS).A total of 249 recordings of 24-hour IOP patterns from 202 participants using a CLS were included. Software was developed to automatically detect eye blinks, and wake and sleep periods. The blink detection method was based on detection of CLS signal peaks greater than a threshold proportional to the signal amplitude. Three methods for automated detection of the sleep and wake periods were evaluated. These relied on blink detection and subsequent comparison of the local signal amplitude with a threshold proportional to the mean signal amplitude. These methods were compared to manual sleep/wake verification. In a pilot, simultaneous video recording of 10 subjects was performed to compare the software to observer-measured blink rates.Mean (SD) age of participants was 57.4 ± 16.5 years (males, 49.5%). There was excellent agreement between software-detected number of blinks and visually measured blinks for both observers (intraclass correlation coefficient [ICC], 0.97 for observer 1; ICC, 0.98 for observer 2). The CLS measured a mean blink frequency of 29.8 ± 15.4 blinks/min, a blink duration of 0.26 ± 0.21 seconds and an interblink interval of 1.91 ± 2.03 seconds. The best method for identifying sleep periods had an accuracy of 95.2 ± 0.5%.Automated analysis of CLS 24-hour IOP recordings can accurately quantify eye blinks, and identify sleep and wake periods.This study sheds new light on the potential importance of eye blinks in glaucoma and may contribute to improved understanding of circadian IOP characteristics.
Project description:Eyeblinks, whether reflexive or voluntary, play an important role in protecting our vision. When viewing pictures, reflexive eyeblinks are known to be modulated by the emotional state induced thereby. More specifically, the hedonic valence (unpleasantness-pleasantness) induced by the picture has been shown to have a linear relationship with the amplitude of a startle blink elicited during picture viewing. This effect has been attributed to congruence between an ongoing state and task demands: an unpleasant emotional state is assumed to bias our attention towards potentially harmful stimuli, such as startle tones. However, recent research suggests that the valence-specific modulation may not be limited to the sensory parts of the reflexive pathway related to startle responses. Here, we examined the effect of emotional picture viewing on voluntary (in response to a written command) eyeblinks in adult humans. Emotional modulation of startle blinks was also evaluated. We found that when viewing unpleasant pictures, the amplitude of reflexive eyeblinks was augmented, but the amplitude of voluntary eyeblinks was unaffected. Nevertheless, the response latencies of voluntary eyeblinks were found to be delayed during the viewing of pleasant and unpleasant relative to neutral pictures. We conclude that these results support the theory that emotional experience augments sensory processing specific to potentially harmful stimuli. Further, the emotional state seems not to exert an effect on voluntarily elicited motor activity.
Project description:Spontaneous eyeblink rates greatly vary among individuals from several blinks to a few dozen blinks per minute. Because dopamine agonists immediately increase the blink rate, individual differences in blink rate are used as a behavioral index of central dopamine functioning. However, an association of the blink rate with polymorphisms in dopamine-related genes has yet not been found. In this study, we demonstrated that a genetic variation of the nicotinic acetylcholine receptor CHRNA4 (rs1044396) increased the blink rate while watching a video. A receiver operating characteristic analysis revealed that the blink rate predicts a genetic variation in the nicotinic receptor gene with a significant discrimination level (0.66, p < 0.004). The present study suggests that differences in sensitivity to acetylcholine because of the genetic variation of the nicotinic receptor are associated with individual differences in spontaneous eye blink rate.
Project description:Electroencephalography (EEG) offers a platform for studying the relationships between behavioral measures, such as blink rate and duration, with neural correlates of fatigue and attention, such as theta and alpha band power. Further, the existence of EEG studies covering a variety of subjects and tasks provides opportunities for the community to better characterize variability of these measures across tasks and subjects. We have implemented an automated pipeline (BLINKER) for extracting ocular indices such as blink rate, blink duration, and blink velocity-amplitude ratios from EEG channels, EOG channels, and/or independent components (ICs). To illustrate the use of our approach, we have applied the pipeline to a large corpus of EEG data (comprising more than 2000 datasets acquired at eight different laboratories) in order to characterize variability of certain ocular indicators across subjects. We also investigate dependence of ocular indices on task in a shooter study. We have implemented our algorithms in a freely available MATLAB toolbox called BLINKER. The toolbox, which is easy to use and can be applied to collections of data without user intervention, can automatically discover which channels or ICs capture blinks. The tools extract blinks, calculate common ocular indices, generate a report for each dataset, dump labeled images of the individual blinks, and provide summary statistics across collections. Users can run BLINKER as a script or as a plugin for EEGLAB. The toolbox is available at https://github.com/VisLab/EEG-Blinks. User documentation and examples appear at http://vislab.github.io/EEG-Blinks/.
Project description:Spontaneous blinking occurs 15-20 times per minute. Although blinking has often been associated with its physiological role of corneal lubrication, there is now increasing behavioral evidence suggesting that blinks are also modulated by cognitive processes such as attention and information processing. Recent low-density electroencephalography (EEG) studies have reported so-called blink-related oscillations (BROs) associated with spontaneous blinking at rest. Delta-band (0.5-4 Hz) BROs are thought to originate from the precuneus region involved in environmental monitoring and awareness, with potential clinical utility in evaluation of disorders of consciousness. However, the neural mechanisms of BROs have not been elucidated. Using magnetoencephalography (MEG), we characterized delta-band BROs in 36 healthy individuals while controlling for background brain activity. Results showed that, compared to pre-blink baseline, delta-band BROs resulted in increased global field power (p < 0.001) and time-frequency spectral power (p < 0.05) at the sensor level, peaking at ~250 ms post-blink maximum. Source localization showed that spontaneous blinks activated the bilateral precuneus (p < 0.05 FWE), and source activity within the precuneus was also consistent with sensor-space results. Crucially, these effects were only observed in the blink condition and were absent in the control condition, demonstrating that results were due to spontaneous blinks rather than as part of the inherent brain activity. The current study represents the first MEG examination of BROs. Our findings suggest that spontaneous blinks activate the precuneus regions consistent with environmental monitoring and awareness, and provide important neuroimaging support for the cognitive role of spontaneous blinks.
Project description:Eye blinks cause disruptions to visual input and are accompanied by rotations of the eyeball . Like every motor action, these eye movements are subject to noise and introduce instabilities in gaze direction across blinks . Accumulating errors across repeated blinks would be debilitating for visual performance. Here, we show that the oculomotor system constantly recalibrates gaze direction during blinks to counteract gaze instability. Observers were instructed to fixate a visual target while gaze direction was recorded and blinks were detected in real time. With every spontaneous blink-while eyelids were closed-the target was displaced laterally by 0.5° (or 1.0°). Most observers reported being unaware of displacements during blinks. After adapting for ?35 blinks, gaze positions after blinks showed significant biases toward the new target position. Automatic eye movements accompanied each blink, and an aftereffect persisted for a few blinks after target displacements were eliminated. No adaptive gaze shift occurred when blinks were simulated with shutter glasses at random time points or actively triggered by observers, or when target displacements were masked by a distracting stimulus. Visual signals during blinks are suppressed by inhibitory mechanisms [3-6], so that small changes across blinks are generally not noticed [7, 8]. Additionally, target displacements during blinks can trigger automatic gaze recalibration, similar to the well-known saccadic adaptation effect [9-11]. This novel mechanism might be specific to the maintenance of gaze direction across blinks or might depend on a more general oculomotor recalibration mechanism adapting gaze position during intrinsically generated disruptions to visual input.
Project description:Domestic animals are sensitive to human cues that facilitate inter-specific communication, including cues to emotional state. The eyes are important in signalling emotions, with the act of narrowing the eyes appearing to be associated with positive emotional communication in a range of species. This study examines the communicatory significance of a widely reported cat behaviour that involves eye narrowing, referred to as the slow blink sequence. Slow blink sequences typically involve a series of half-blinks followed by either a prolonged eye narrow or an eye closure. Our first experiment revealed that cat half-blinks and eye narrowing occurred more frequently in response to owners’ slow blink stimuli towards their cats (compared to no owner–cat interaction). In a second experiment, this time where an experimenter provided the slow blink stimulus, cats had a higher propensity to approach the experimenter after a slow blink interaction than when they had adopted a neutral expression. Collectively, our results suggest that slow blink sequences may function as a form of positive emotional communication between cats and humans.