Eye Rotation Research Articles

Artifact reduction in lenslet array near-eye displays

Lenslet array near-eye displays are a revolutionary technology that generates a virtual image in the field of view of the observer. Although this technology is advantageous in creating compact near-eye displays, undesirable artifacts occur when the user pupil moves outside of the pupil practical movable region (PPMR). Even with dynamic image updating based on eye-tracking techniques, artifacts can still be perceived when human eyes turn rapidly. To enlarge PPMR, we proposed a new rendering method in previous work. To improve the rendering speed in the eye tracking system, look-up tables are used. The disadvantage of the onboard system is the large memory consumption. In this study, we analyzed the system parameters of the incident pupil and pupil margin light columns, the feasibility of the optimized system, and evaluated the optimized system that can adapt to the maximum velocity of the saccadic pupil movement. We optimized the rendering method to reduce memory consumption in the process of generating microdisplay images. In addition, we provide GPU rendering method to improve system speed and reduce system latency to meet the maximum human eye rotation speed. We conducted user studies to evaluate the effect of the method using the optimized rendering method combined with eye tracking to reduce artifacts for fast eye rotation on different images and videos. Results showed that our method effectively reduced artifacts via the optimized rendering method with eye tracking, which adapted to faster human eye movements.

Neurons in Primate Area MSTd Signal Eye Movement Direction Inferred from Dynamic Perspective Cues in Optic Flow.

Smooth eye movements are common during natural viewing; we frequently rotate our eyes to track moving objects or to maintain fixation on an object during self-movement. Reliable information about smooth eye movements is crucial to various neural computations, such as estimating heading from optic flow or judging depth from motion parallax. While it is well established that extraretinal signals (e.g., efference copies of motor commands) carry critical information about eye velocity, the rotational optic flow field produced by eye rotations also carries valuable information. Although previous work has shown that dynamic perspective cues in optic flow can be used in computations that require estimates of eye velocity, it has remained unclear where and how the brain processes these visual cues and how they are integrated with extraretinal signals regarding eye rotation. We examined how neurons in the dorsal region of the medial superior temporal area (MSTd) of two male rhesus monkeys represent the direction of smooth pursuit eye movements based on both visual cues (dynamic perspective) and extraretinal signals. We find that most MSTd neurons have matched preferences for the direction of eye rotation based on visual and extraretinal signals. Moreover, neural responses to combinations of these signals are well predicted by a weighted linear summation model. These findings demonstrate a neural substrate for representing the velocity of smooth eye movements based on rotational optic flow and establish area MSTd as a key node for integrating visual and extraretinal signals into a more generalized representation of smooth eye movements.SIGNIFICANCE STATEMENT We frequently rotate our eyes to smoothly track objects of interest during self-motion. Information about eye velocity is crucial for a variety of computations performed by the brain, including depth perception and heading perception. Traditionally, information about eye rotation has been thought to arise mainly from extraretinal signals, such as efference copies of motor commands. Previous work shows that eye velocity can also be inferred from rotational optic flow that accompanies smooth eye movements, but the neural origins of these visual signals about eye rotation have remained unknown. We demonstrate that macaque neurons signal the direction of smooth eye rotation based on visual signals, and that they integrate both visual and extraretinal signals regarding eye rotation in a congruent fashion.

The impact of horizontal eye movements versus intraocular pressure on optic nerve head biomechanics: A tridimensional finite element analysis study

It has been proposed that eye movements could be related to glaucoma development. This research aimed to compare the impact of intraocular pressure (IOP) versus horizontal duction on optic nerve head (ONH) strains. Thus, a tridimensional finite element model of the eye including the three tunics of the eye, all of the meninges, and the subarachnoid space (SAS) was developed using a series of medical tests and anatomical data. The ONH was divided into 22 subregions, and the model was subjected to 21 different eye pressures, as well as 24 different degrees of adduction and abduction ranging from 0.5° to 12°. Mean deformations were documented along anatomical axes and in principal directions. Additionally, the impact of tissue stiffness was assessed. The results show no statistically significant differences between the lamina cribrosa (LC) strains due to eye rotation and IOP variation. However, when assessing LC regions some experienced a reduction in principal strains following a 12° duction, while after the IOP reached 12 mmHg, all LC subzones showed an increase in strains. From an anatomical perspective, the effect on the ONH following 12° duction was opposite to that observed after a rise in IOP. Moreover, high strain dispersion inside the ONH subregions was obtained with lateral eye movements, which was not observed with increased IOP and variation. Finally, SAS and orbital fat stiffness strongly influenced ONH strains during eye movements, while SAS stiffness was also influential under ocular hypertension. Even if horizontal eye movements cause large ONH deformations, their biomechanical effect would be markedly distinct from that induced by IOP. It could be predicted that, at least in physiological conditions, their potential to cause axonal injury would not be so relevant. Thus, a causative role in glaucoma does not appear likely. By contrast, an important role of SAS would be expectable.

The effect of sustained eye rotation upon eye length in healthy myopic adults.

The aim of the study was to determine whether ocular movement can affect the shape of the globe and lead to measurable change in axial and peripheral eye length. Ten subjects aged 18-30 years (6 M/4 F) participated with informed consent. The mean spherical equivalent refractive error was ≤-1.00 DS with cylindrical refraction <-1.25 DC. One drop of tropicamide hydrochloride 1% was instilled 20 min before measurement to induce mydriasis and mild cycloplegia. Using IOLMaster, eye length was measured centrally and temporally (25° off-axis) in four different positions. Subjects then rotated their eyes 25° in the temporal direction to fixate on a target for 10 min. After that, the same measurements were repeated. Before rotation, the group mean peripheral eye length was significantly shorter than the central eye length (P < 0.05). There was no significant variation in central or peripheral eye length due to off-axis fixation, either after the initial eye rotation or after fixation for 10 min at the off-axis point. The difference between central and peripheral eye lengths was maintained after 10 min of temporal fixation (P < 0.05). Peripheral eye length was shorter than central eye length showing the prolate shape associated with myopia. The action of the extraocular muscles on the globe has no significant effect upon the retinal shape assessed by off-axis eye length measurement in myopic subjects.

A Simplified Analytical Solution for the Computation of Machine Path in Filament Winding of Cylindrical Angle-Ply and Double-Double Structures

This paper presents a simplified computation approach for the machine path (or winding trajectory) of grid structures and tubes with a circular cross-section and angle-ply or double-double layup. The solution for the machine path is given through controllable degrees of freedom of a low-cost two-axis filament winding machine (FWM): mandrel rotation and translation of the delivery eye along the axis of the mandrel. The efficiency of the analytical solution for the machine path of the FWM was ascertained by automated laying the cotton thread over the geodesic and non-geodesic groove imprinted on the surface of a cylindrical polylactide mandrel. These results validated the possibility of manufacturing cylindrical composite structures with an angle-ply layup or double-double stacking sequence, without the need for expensive software, making the winding technology accessible to society and promoting university extension.

Role of locomotor efference copy in vertebrate gaze stabilization.

Vertebrate locomotion presents a major challenge for maintaining visual acuity due to head movements resulting from the intimate biomechanical coupling with the propulsive musculoskeletal system. Retinal image stabilization has been traditionally ascribed to the transformation of motion-related sensory feedback into counteracting ocular motor commands. However, extensive exploration of spontaneously active semi-intact and isolated brain/spinal cord preparations of the amphibian Xenopus laevis, have revealed that efference copies (ECs) of the spinal motor program that generates axial- or limb-based propulsion directly drive compensatory eye movements. During fictive locomotion in larvae, ascending ECs from rostral spinal central pattern generating (CPG) circuitry are relayed through a defined ascending pathway to the mid- and hindbrain ocular motor nuclei to produce conjugate eye rotations during tail-based undulatory swimming in the intact animal. In post-metamorphic adult frogs, this spinal rhythmic command switches to a bilaterally-synchronous burst pattern that is appropriate for generating convergent eye movements required for maintaining image stability during limb kick-based rectilinear forward propulsion. The transition between these two fundamentally different coupling patterns is underpinned by the emergence of altered trajectories in spino-ocular motor coupling pathways that occur gradually during metamorphosis, providing a goal-specific, morpho-functional plasticity that ensures retinal image stability irrespective of locomotor mode. Although the functional impact of predictive ECs produced by the locomotory CPG matches the spatio-temporal specificity of reactive sensory-motor responses, rather than contributing additively to image stabilization, horizontal vestibulo-ocular reflexes (VORs) are selectively suppressed during intense locomotor CPG activity. This is achieved at least in part by an EC-mediated attenuation of mechano-electrical encoding at the vestibular sensory periphery. Thus, locomotor ECs and their potential suppressive impact on vestibular sensory-motor processing, both of which have now been reported in other vertebrates including humans, appear to play an important role in the maintenance of stable vision during active body displacements.

Eye-Head-Body Coordination in the Motor-Memory Trade-off

Previous studies have demonstrated that people trade off between expending motor effort and memorization effort when completing a copying task that requires looking in different directions to gather information. When information is easy to gather with minimal movement, people choose to look more frequently and rely on less on memorization, however, they reduce motor effort and rely on memory more when looking requires larger (and more effortful) shifts of gaze. This paper investigated the eye-head-body movements that guided looking as well as participants’ trade-off between using motor effort and memory in a copying task. We add to prior work by characterizing the coordination between eyes, head, and body required to look at targets at different angles. In the task, participants copied models onto a board while wearing a mobile eye tracker that measured eye rotations and motion sensors that measured head rotations. We manipulated the angle of the model relative to the participant and the memorization difficulty of the models. Results showed that eye movements contributed more to small gaze shifts but the head and body contributed more as the angle of the target increased (requiring larger amplitude shifts of gaze). Participants chose to look frequently when models were adjacent to the workspace, but chose to rely more on memory for models that required greater shifts of gaze. Memorization difficulty affected the trade-off such that participants used more memory when the models were easy to remember. We discuss how participants’ decisions to look versus remember may depend on the contribution of eyes, head, and body to shift gaze by varying amplitudes.

How vergence influences the perception of being looked at.

Perceiving other people's direct gaze is important for many areas of everyday activity. For horizontal and vertical eye movements, the area of being looked at, known as the cone of gaze, has been well explored. Previous research has shown a range of eye rotations (up to eccentricities of 4°-9°) that people accept as direct gaze. Vergence is an important cue for perceiving the depth of fixation. This study examines the range of vergence angles that support the perception of being looked at. In two experiments, observers adjusted the degree of vergence of the lookers' eyes until they felt just (not) looked at. The first experiment also asked to adjust the point of being exactly looked at, which was 0° (parallel eyes). The thresholds of being just (not) looked at were around 4.5° of convergence and 2.5° divergence, which results in a depth of 7° of vergence. This depth was replicated in Experiment 2, while the thresholds of convergence (3.5°) and divergence (3.5°) slightly differ from Experiment 1. The results indicate a consistent area of vergences being accepted as direct gaze, yielding first-time evidence for a third dimension-the depth dimension-of direct gaze.

Simultaneous multi-channel near-eye display: a holographic retinal projection display with large information content

Augmented reality (AR) near-eye displays (NEDs) are emerging as the next-generation display platform. The existing AR NED only present one single video channel at a time, same as traditional media such as TVs and smartphones. In this Letter, to the best of our knowledge, we propose for the first time a multi-channel holographic retinal projection display (RPD), which can provide multi-channel image sources simultaneously, thus greatly increasing the information content. Due to the superposition capacity of a hologram, multiple images are projected to different viewpoints simultaneously through multiple spherical wave encoding, so that the viewer can switch among playing channels very fast through eye rotation. A full-color dynamic multi-channel holographic near-eye display is demonstrated in the optical experiment. The proposed method provides a good prospect that the future AR glasses can play dozens of video channels in parallel, and the user can switch among channels freely and efficiently just through a simple eye rotation.

Impact of walking speed and motion adaptation on optokinetic nystagmus-like head movements in the blowfly Calliphora

The optokinetic nystagmus is a gaze-stabilizing mechanism reducing motion blur by rapid eye rotations against the direction of visual motion, followed by slower syndirectional eye movements minimizing retinal slip speed. Flies control their gaze through head turns controlled by neck motor neurons receiving input directly, or via descending neurons, from well-characterized directional-selective interneurons sensitive to visual wide-field motion. Locomotion increases the gain and speed sensitivity of these interneurons, while visual motion adaptation in walking animals has the opposite effects. To find out whether flies perform an optokinetic nystagmus, and how it may be affected by locomotion and visual motion adaptation, we recorded head movements of blowflies on a trackball stimulated by progressive and rotational visual motion. Flies flexibly responded to rotational stimuli with optokinetic nystagmus-like head movements, independent of their locomotor state. The temporal frequency tuning of these movements, though matching that of the upstream directional-selective interneurons, was only mildly modulated by walking speed or visual motion adaptation. Our results suggest flies flexibly control their gaze to compensate for rotational wide-field motion by a mechanism similar to an optokinetic nystagmus. Surprisingly, the mechanism is less state-dependent than the response properties of directional-selective interneurons providing input to the neck motor system.

Prevalence of Hypocalcemic Fits in Exclusively Breast Fed Infants

Aim: To determine the prevalence of hypocalcemia fits in exclusively breast fed infants. Study design: Prospective study. Place and duration of study: Department of Paediatric Medicine, Abbas Institute of Medical Sciences/Medical College Muzafarabad AJ Kashmir from 01-04-2021 to 31-03-2022. Methodology: One hundred breast fed infants were enrolled. A 0.5cc blood of child was withdrawn for conductance of serum calcium and 25(OH) vitamin D3 test while 2cc of mother blood was also withdrawn for analyzing their calcium levels as well as vitamin D status in duplicate batches. Radiological imaging through x ray image of wrist for detection of rickets was performed in each infant. Infants having complain of fits were specifically observed fit/seizure time duration of the fit, the time when it occurred, eye rotation and cyanosis condition. Any family history regarding epilepsy especially in mothers was also noted. Results: The mean age of the infants was 5.5±2.3 months with a range of 1-12 months. Majority of the infants were male gender with a parentage of 66% while there were 34% female gender infants. Within the total number of infants included 30 children were having clinically defined rickets with 25 such infants who were having vitamin D level below the level of 20ng/ml. Conclusion: There is a low prevalence of hypocalcemia fit among breast fed infants. Keywords: Prevalence, Hypocalcemic fits, Breast fed infants.

The amplitude of small eye movements can be accurately estimated with video-based eye trackers

Estimating the gaze direction with a digital video-based pupil and corneal reflection (P-CR) eye tracker is challenging partly since a video camera is limited in terms of spatial and temporal resolution, and because the captured eye images contain noise. Through computer simulation, we evaluated the localization accuracy of pupil-, and CR centers in the eye image for small eye rotations (≪ 1 deg). Results highlight how inaccuracies in center localization are related to 1) how many pixels the pupil and CR span in the eye camera image, 2) the method to compute the center of the pupil and CRs, and 3) the level of image noise. Our results provide a possible explanation to why the amplitude of small saccades may not be accurately estimated by many currently used video-based eye trackers. We conclude that eye movements with arbitrarily small amplitudes can be accurately estimated using the P-CR eye-tracking principle given that the level of image noise is low and the pupil and CR span enough pixels in the eye camera, or if localization of the CR is based on the intensity values in the eye image instead of a binary representation.

Persistent horizontal and vertical, MR-induced nystagmus in resting state Human Connectome Project data

ObjectiveStrong magnetic fields from magnetic resonance (MR) scanners induce a Lorentz force that contributes to vertigo and persistent nystagmus. Prior studies have reported a predominantly horizontal direction for healthy subjects in a 7 Tesla (T) MR scanner, with slow phase velocity (SPV) dependent on head orientation. Less is known about vestibular signal behavior for subjects in a weaker, 3T magnetic field, the standard strength used in the Human Connectome Project (HCP). The purpose of this study is to characterize the form and magnitude of nystagmus induced at 3T. MethodsForty-two subjects were studied after being introduced head-first, supine into a Siemens Prisma 3T scanner. Eye movements were recorded in four separate acquisitions over 20 min. A biometric eye model was fitted to the recordings to derive rotational eye position and then SPV. An anatomical template of the semi-circular canals was fitted to the T2 anatomical image from each subject, and used to derive the angle of the B0 magnetic field with respect to the vestibular apparatus. ResultsRecordings from 37 subjects yielded valid measures of eye movements. The population-mean SPV ± SD for the horizontal component was -1.38 ± 1.27 deg/sec, and vertical component was -0.93 ± 1.44 deg/sec, corresponding to drift movement in the rightward and downward direction. Although there was substantial inter-subject variability, persistent nystagmus was present in half of subjects with no significant adaptation over the 20 min scanning period. The amplitude of vertical drift was correlated with the roll angle of the vestibular system, with a non-zero vertical SPV present at a 0 degree roll. InterpretationNon-habituating vestibular signals of varying amplitude are present in resting state data collected at 3T.

Positions of the horizontal and vertical centre of rotation in eyes with different refractive errors.

PurposeTo determine how the position of the centre of rotation of the eyeball is related to axial length and refractive error when horizontal and vertical eye movements are performed.MethodsA custom‐built eye tracker was used that determined the centre of rotation of the eye (COR) from lateral displacements of the pupil centre. Horizontal and vertical eye movements were studied in the right eyes, and each measurement performed five times in 59 subjects (32 females) with an average age of 36.6 ± 9.1 years. Spherical equivalent refractive errors ranged from −9.7 to +6.8 D with an average error of −1.5 ± 2.9 D. Axial lengths were measured with the ZEISS IOL Master 500.ResultsThe mean horizontal centre of rotation (COR) of the right eye for a saccade from 0° to ±11.9° was 15.3 ± 1.5 mm behind the corneal apex, while the average vertical COR for the same angle of eccentricity was 12.5 ± 1.4 mm, indicating that the horizontal COR was 2.8 ± 1.7 mm behind the vertical COR. In right eyes, horizontal COR was significantly correlated with axial length (r = 0.28, p = 0.02) but not with the spherical equivalent refractive error (r = 0.39, p = 0.90). Similarly, vertical COR was significantly correlated with axial length (r = 0.25, p = 0.03) but not with the spherical equivalent refractive error (r = 0.17, p = 0.90).ConclusionsWhile it might be expected that the COR is dependent on axial length, the correlation was not strong. Interestingly, the location of the COR was substantially different for horizontal and vertical eye movements which may relate to the flatter curvature of the eyeball in the vertical meridian, compared to the horizontal, as described in previous studies.

Iris Recognition Using Low-Level CNN Layers Without Training and Single Matching

Iris is one of the most accurate biometrics. This has led to the successful development of large-scale applications. However, with population growth, and new international applications, datasets are constantly increasing in size, requiring more robust and faster methods. Many descriptors and feature extractors have been developed to extract features that represent the iris biometric pattern. Most of them have been designed by human experts and require a bit-shifting process to increase their robustness to eye rotations, at the expense of increased matching time. We propose a fast iris recognition method that requires a single matching operation and is based on pre-trained image classification models as feature extractors. Our approach uses the filters of the first layers from Convolutional Neural Networks as feature extractors and does not require fine-tuning for new datasets. Since our selected features extracted from convolutional layers encode the iris surface, they have the advantage of not being restricted to specific spatial positions. Thus, it is not necessary to perform a bit-shifting process in the matching stage, eliminating a significant number of computations. Additionally, to mitigate the effect produced by the mask border in rubber-sheet images, we propose filtering the feature map tensors by masking their channels and selecting the most relevant features. Our method was assessed on the publicly available datasets CASIA Iris Lamp and CASIA Iris Thousand, and showed significant improvement both in accuracy and in matching time.

Extent of foveal fixation with eye rotation in emmetropes and myopes

PurposeThis pilot study aimed to investigate the maximum extension of foveal fixation in the horizontal direction among young adults in both emmetropes and myopes. Methods35 participants (28 emmetropes and 7 myopes) were included. Participants with restricted extra-ocular mobility, end gaze nystagmus, and/or any other ocular pathology were excluded. Visual acuity (VA) was used as a surrogate measure of foveal fixation. VA was determined using a staircase procedure with 8 reversals. The average of the last 5 reversals was taken as the thresholds. VA acuity was measured at different gaze eccentricities along nasal and temporal visual field meridian. The eccentricity at which VA drops significantly was taken as the maximum extent of foveal fixation. A bilinear fit regression model was used to investigate the drop in the VA in both nasal and the temporal direction. ResultsEmmetropes can foveate up to 35 ± 2° in nasal and 40 ± 3° in temporal direction and myopes can foveate up to 38° in both nasal and temporal directions. Paired student t-test showed a significant difference in foveal fixation between nasal and temporal direction for emmetropes (P<0.001) but not in myopes (P = 0.168). An unpaired student t-test showed a significant difference in foveal fixation for nasal direction between myopes and emmetropes (P = 0.01). However, no statistically significant difference was found in foveal fixation for temporal direction between myopes and emmetropes (P = 0.792). ConclusionThe eye rotation does not necessarily match with the extent of foveal fixation at extreme eye rotation. Eyes can fixate only up to 35° nasally and 40° temporally maintaing their maximum visual acuity.

Real-Time MRI Reveals Unique Insight into the Full Kinematics of Eye Movements.

Our eyes are constantly in motion and the various kinds of eye movements are closely linked to many aspects of human cognitive processing. Measuring all possible eye movements unobtrusively is not achievable with current methods. Video-based eye-trackers only measure rotational but not translational motion of the eye, require a calibration process relying on the participant’s self-report of accurate fixation, and do not work if vision of the eyeball is blocked. Scleral search coils attach physical weight on the eyeball and also do not measure translation. Here, we describe a novel and fully automated method to use real-time magnetic resonance imaging (MRI) for eye tracking. We achieved a temporal resolution sufficient to measure eye rotations and translations as short as those that occur within a blink and behind a closed eyelid. To demonstrate this method, we measured the full extent of the blink-related eye movement for two individuals, suggesting that the eye approaches a holding position during lid closure and can move by as much as 35° in rotation and 2 mm in translation. We also investigated the coordination of gaze shifts with blinks. We found that the gaze shift is tightly coupled in time to the translational blink movement and that blinks can induce significant temporal shifts of the gaze trajectory between left and right eye. Our MR-based Eye Tracking (MREyeTrack) method allows measurement of eye movements in terms of both translation and rotation and enables new opportunities for studying ocular motility and its disorders.

Visual pursuit behavior in mice maintains the pursued prey on the retinal region with least optic flow.

Mice have a large visual field that is constantly stabilized by vestibular ocular reflex (VOR) driven eye rotations that counter head-rotations. While maintaining their extensive visual coverage is advantageous for predator detection, mice also track and capture prey using vision. However, in the freely moving animal quantifying object location in the field of view is challenging. Here, we developed a method to digitally reconstruct and quantify the visual scene of freely moving mice performing a visually based prey capture task. By isolating the visual sense and combining a mouse eye optic model with the head and eye rotations, the detailed reconstruction of the digital environment and retinal features were projected onto the corneal surface for comparison, and updated throughout the behavior. By quantifying the spatial location of objects in the visual scene and their motion throughout the behavior, we show that the prey image consistently falls within a small area of the VOR-stabilized visual field. This functional focus coincides with the region of minimal optic flow within the visual field and consequently area of minimal motion-induced image-blur, as during pursuit mice ran directly toward the prey. The functional focus lies in the upper-temporal part of the retina and coincides with the reported high density-region of Alpha-ON sustained retinal ganglion cells.

Effective selection of the optimal virtual reality (VR) lens interval of VR devices using the test patterns of the different shapes for the left and right eyes

AbstractSelection of the optimal virtual reality (VR) lens interval LI between two convex lenses of a VR device is important for the comfort of viewers. This study examined how the participants selected LI for two types of test patterns. Twenty‐one participants with interpupillary distances (IPDs) of 59–68 mm were selected. When the participants were asked to change the LI to match specific positions of the test pattern in which the shapes for the two eyes were different, the selected values of LI did not depend on the initial lens distances. When they were asked to change LI for their best viewing distances using the test pattern with the same shapes for two eyes, the selected values strongly depended on the initial lens conditions. This dependence can be attributed to the finite range of eye rotation inside which binocular fusion can occur. No noticeable dependence of the selected values on IPD was observed. Excessive eye rotation to enable binocular fusion can cause eye strain. In the former test pattern, binocular fusion does not occur, and each eye is aligned along its fusion‐free eye position with little eye strain. Hence, the former test pattern using the different shapes is preferable for controlling the lens interval.

Vestibular contributions to the Romberg test: Testing semicircular canal and otolith function.

Normal stance relies on three sensory inputs: vision, proprioception and vestibular function. The Romberg test, trying to stand with feet together and eyes closed, is familiar to every medical student as a test of distal proprioceptive impairment. It remains the best known of Romberg's many remarkable contributions to clinical neurology. In Romberg's time almost nothing was known about the function of the vestibular system. We now know that standing with the eyes closed on a compliant rather than a firm surface is more a test of vestibular than proprioceptive function. Peripheral vestibular function tests in clinical use today all rely on measurements of oligosynaptic brainstem reflexes. Short-latency eye rotations in response to rapid, brief head rotations (head impulses) give an accurate, robust and reproducible measure of the function of any and each of the six semicircular canals. Short-latency evoked potentials from sternomastoid and inferior oblique muscles in response to loud clicks or skull taps (vestibular evoked myogenic potentials) give an accurate and reproducible measure of the function of each and any of the four otolith organs. In the present paper, we briefly review what is now known about the anatomy and physiology of the peripheral receptors and brainstem pathways mediating these reflexes and examine how this knowledge can help interpret the Romberg test.