Search

This work addresses an impractical and unnatural constraint that has been generally enforced in state-of-the-art electrooculography (EOG)-based gaze estimation methods, that of maintaining a stationary head pose and position. Specifically, this work proposes an EOG-based gaze angle (GA) estimation method that accommodates natural variations in the user's head pose and position. The EOG data collected under non-stationary head conditions, which was used in this work to validate the proposed method, is also being made publicly available. This work generalises a two-eye verging gaze geometrical model to cater for arbitrary head poses and positions, and also models the dynamics of the vestibulo-ocular reflex (VOR), which refers to the eye-head coordination that normally takes place during gaze shifts under unrestrained head conditions. These methods are validated by incorporating them within a published multiple-model framework for GA estimation. When applied to short EOG data segments, a horizontal and vertical GA estimation error of 1.85 ± 0.51 ° and 2.19 ± 0.62 ° , respectively, and an eye movement detection and labelling F-score close to 90% were obtained. These results are comparable to those reported previously under stationary head conditions. This work demonstrates that accurate GA estimation and eye movement detection and labelling can be achieved using EOG signals, even when the user's head is not stationary. This work eliminates the need for users to maintain a stationary head pose and position, a common constraint in the field, thus introducing an EOG-based GA estimation method that allows users to move their heads naturally. • Real-time-implementable algorithm for EOG-based gaze estimation. • Modelling of the Vestibulo Ocular Reflex. • Multiple-model framework including models for fixations, saccades, blinks and VORs. • Gaze estimation while compensating for baseline drift and head movement. • Sample-by-sample labelling of EOG signals. [ABSTRACT FROM AUTHOR]

The present study aimed to analyse the impact of vestibulo-ocular reflex (VOR) gain deficit on postural control (PC) in children with sensorineural hearing loss. A retrospective study included 55 children with sensorineural hearing loss between 4 and 17 years of age. The Video Head Impulse Test (vHIT®) was used to assess semicircular canal function. PC was assessed on the Balance Quest® posturographic platform testing sensory organisation. Spatial and temporal postural parameters (area and mean speed of centre of pressure oscillation, spectral power index) in the OKN-U condition (optokinetic with unstable platform) were significantly better in children with than without VOR deficit. Posturographic exploration in the OKN-U condition can screen for semicircular canal deficit in hearing-impaired children. VOR deficit also seems to predict PC deficit. [ABSTRACT FROM AUTHOR]

The orientation of human eyes is uniquely defined with respect to their gaze direction, known as Donders' law. Further, the manner in which the eyes follow Donders' law varies as a function of the situation. When the head is stationary, the Donders' surfaces are flat planes but they tilt when eye fixation distance changes. These planes also shift and rotate when head orientation changes with respect to the direction of gravito-inertial acceleration. When the head is free to rotate, the Donders' surfaces are twisted. In this paper, we present a systematic method to analyze the kinematics of the eye under different gaze situations utilizing the measurement of alignment between various coordinate frames. Kinematic equations are presented for various eye movements ranging from simple head-fixed monocular shifts of eye gaze to complex eye-head shifts of gaze. At each stage, we show that simulated eye orientations that derived from our equations are able to capture the variations of Donders' surfaces and they are comparable with experimental results in the literature. The final equations we propose provide the unified kinematics of head-upright far gaze, head-upright binocular fixation, head static tilted monocular gaze and head-free monocular gaze. [ABSTRACT FROM AUTHOR]

Background/purpose: To evaluate the complexity of vestibular-ocular reflex (VOR) in patients with acute unilateral vestibular loss (AUVL) via entropy analysis of head impulses.Methods: Horizontal head impulse test (HIT) with high-velocity alternating directions was used to evaluate 12 participants with AUVL and 16 healthy volunteers. Wireless electro-oculography and electronic gyrometry were used to acquire eye positional signals and head velocity signals. The eye velocity signals were then obtained through differentiation, band-pass filtering. The approximate entropy of eye velocity to head velocity (RApEn) was used to evaluate chaos property. VOR gain, gain asymmetry ratio, and RApEn asymmetry ratio were also used to compare the groups.Results: For the lesion-side HIT of the patient group, the mean VOR gain was significantly lower and the mean RApEn was significantly greater compared with both nonlesion-side HIT and healthy controls (p < 0.01, one-way analysis of variance). Both the RApEn asymmetry ratio and gain asymmetry ratio of the AUVL group were significantly greater compared with those of the control group (p < 0.05, independent sample t test).Conclusion: Entropy and gain analysis of HIT using wireless electro-oculography system could be used to detect the VOR dysfunctions of AUVL and may become effective methods for evaluating vestibular disorders. [ABSTRACT FROM AUTHOR]

Abstract: An anatomical model is proposed to model the command of saccadic eye movements. This model of movement control is that its structure is consistent with general anatomy, cell connectivity and functioning of the cerebellar pathways, i.e. motor orders processing, to compute an approximate inverse function of the bio-mechanical function of eye and head sensors. Its parameters are deduced from a stability analysis constraint and system identification to produce desired output. In this research, a predicting element, necessary for inversion and thus for movement accuracy, is modeled by an artificial neural network which is an Adaptive Neuro Fuzzy Inference System (ANFIS) with online learning. According to anatomy, in this model, in the first step, the proposed ANN is trained with a slow movement in a closed-loop pathway to initiate a primary structure. In the next steps, the model is able to accurately simulate saccadic eye movements and keeps the online learning to reduce the error. Experiment results show that the proposed model has been stable in different saccadic movements and error tends to neglected values. [Copyright &y& Elsevier]

Abstract: In Xenopus laevis tadpoles, effects of asymmetrical light conditions on the roll-induced vestibuloocular reflex (rVOR) were tested for the developmental period between stage 47 and 49. For comparison, the rVOR was tested in dim- and high-symmetrical light environments. Test parameters were the rVOR gain and rVOR amplitude. Under all light conditions, the rVOR increased from tadpole stage 47 to 49. For all stages, the asymmetrical light field induced the strongest response, the dim light field the weakest one. The response for the left and right eye was identical, even if the tadpoles were tested under asymmetrical light conditions. The experiments can be considered as hints (1) for an age-dependent light sensitivity of vestibular neurons, and (2) for the existence of control systems for coordinated eye movements that has its origin in the proprioceptors of the extraocular eye muscles. [Copyright &y& Elsevier]

Abstract: Recording of ocular nystagmus during vestibular tests does not measure the true response of the vestibulo-ocular reflex (VOR), because the VOR response (so-called slow phase of nystagmus) is interrupted by resetting saccades (so-called fast phase of nystagmus). In order to extract the real VOR contribution, saccades must be removed. In most of the nystagmus processing algorithms, saccade removal requires a human operator to choose a suitable eye velocity threshold able to separate fast from slow nystagmus phases. In the present report a fully automatic removal system is presented which selects an optimal velocity threshold by computing the VOR frequency response and maximizing its coherence function. [Copyright &y& Elsevier]

Abstract: We examined how the gain of the torsional vestibulo-ocular reflex (VOR) (defined as the instantaneous eye velocity divided by inverted head velocity) in normal humans is affected by eye position, target distance, and the plane of head rotation. In six normal subjects we measured three-dimensional (3D) eye and head rotation axes using scleral search coils, and 6D head position using a magnetic angular and linear position measurement device, during low-amplitude (∼20°), high-velocity (∼200°/s), high-acceleration (∼4000°/s2) rapid head rotations or ‘impulses.’ Head impulses were imposed manually and delivered in five planes: yaw (horizontal canal plane), pitch, roll, left anterior-right posterior canal plane (LARP), and right anterior-left posterior canal plane (RALP). Subjects were instructed to fix on one of six targets at eye level. Targets were either straight-ahead, 20° left or 20° right from midline, at distance 15 or 124cm from the subject. Two subjects also looked at more eccentric targets, 30° left or 30° right from midline. We found that the vertical and horizontal VOR gains increased with the proximity of the target to the subject. Previous studies suggest that the torsional VOR gain should decrease with target proximity. We found, however, that the torsional VOR gain did not change for all planes of head rotation and for both target distances. We also found a dynamic misalignment of the vertical positions of the eyes during the torsional VOR, which was greatest during near viewing with symmetric convergence. This dynamic vertical skew during the torsional VOR arises, in part, because when the eyes are converged, the optical axes are not parallel to the naso-occipital axes around which the eyes are rotating. In five of six subjects, the average skew ranged 0.9°–2.9° and was reduced to <0.4° by a ‘torsional’ quick-phase (around the naso-occipital axis) occurring <110ms after the onset of the impulse. We propose that the torsional quick-phase mechanism during the torsional VOR could serve at least three functions: (1) resetting the retinal meridians closer to their usual orientation in the head, (2) correcting for the ‘skew’ deviation created by misalignment between the axes around which the eyes are rotating and the line of sight, and (3) taking the eyes back toward Listing’s plane. [Copyright &y& Elsevier]

Abstract: We studied ocular asymmetries and orienting responses induced by angular rotation in rabbits with binocular video recordings. Slow phase velocities were significantly larger in the eye moving temporonasally than nasotemporally. The eyes also converged and pitched down during rotation, which increased and refocused binocular overlap in the visual fields. Eye position also shifted into the slow phase direction. Vergence and pitch outlasted the induced nystagmus, suggesting that they were generated by a separate vestibulo-oculomotor subsystem(s). Thus, mechanisms in the rabbit increase compensatory eye velocity in the eye that leads into the direction of rotation and enhance binocular vision. [Copyright &y& Elsevier]

Abstract: Previous studies indicated that less motion smear is perceived when a physically stationary target is presented during voluntary eye movements than when similar retinal-image motion occurs during steady fixation. In this study, we assessed whether the perception of motion smear is attenuated also during the involuntary vestibulo-ocular reflex (VOR). Normal observers matched the length of perceived smear in two experimental conditions that were designed to produce similar trajectories of retinal image motion. In the fixation condition, a small bright target was presented for a duration of 50–200ms in rightward or leftward motion, while the observer remained stationary and maintained fixation. In the VOR condition, the target moved along with the observer, who underwent full-body rotation around a vertical axis in darkness. Horizontal eye movement recordings during VOR trials allowed us to calculate the velocity of retinal image motion on each VOR trial. The principal result was that the extent of perceived motion smear was significantly less during VOR than fixation trials, particularly for target durations of 100ms or longer. These findings support the conclusion that extra-retinal signals during the involuntary VOR contribute to a reduction of perceived motion smear. [Copyright &y& Elsevier]

Despite nearly perfect gaze stability during natural head movements, the amplitude of the vestibulo-ocular reflex during passive head and body translation (TVOR) has been consistently reported to be undercompensatory during near target viewing. Here we have compared the rhesus monkey TVOR during pure head and body translation with the eye movements generated during eccentric yaw rotations, where both semicircular canal and otolith signals are activated. We found a significant increase in both the near target TVOR amplitude and its viewing distance dependence during eccentric rotations, as compared to pure translations. We conclude that the simultaneous activation of the horizontal semicircular canals result in an improvement of the viewing distance-dependence of the rhesus monkey TVOR. [Copyright &y& Elsevier]

The translational vestibulo-ocular reflex (tVOR) stabilizes an image on the fovea during linear movements of the head. It has been suggested that the tVOR may share pathways with the pursuit system. We asked whether the tVOR and pursuit would be similar in their behavior relative to Listing’s Law. We compared torsional eye velocity as a function of vertical orbital position during interaural translation, pursuit, and yaw-axis rotation. We found that the eye-position-dependence of torsion was similar during translation and pursuit, which differed from that during yaw-axis rotation. These findings further support a close relationship between the mechanisms that generate pursuit and the tVOR. [Copyright &y& Elsevier]

The image on a head mounted display (HMD) moves in the same direction as the viewer''s head during head motion. Horizontal head motion causes eye movement in the opposite direction (vestibulo-ocular reflex (VOR)), but the VOR is suppressed visually by images on the HMD. We measured visual suppression of torsional eye movements evoked by head roll motion. Velocity gains of torsional VOR, VOR suppressed visually by the HMD and visually induced torsion were −0.45, −0.34, and 0.02, respectively. Vestibular input overcomes visual input in counterroll eye movements, visual input suppresses vestibular input in horizontal VOR. These complex interactions may underly the motion sickness experienced by users of HMDs. [Copyright &y& Elsevier]

Labyrinthine defective subjects (LDS) experience oscillopsia during head movements due to the absence of the vestibulo-ocular reflex (VOR). The purpose of this study was to compare horizontal and vertical visual motion detection in LDS during (i) body-stationary and (ii) horizontal whole-body oscillation conditions. Twelve LDS and controls detected the onset of drift direction of a grating that moved with accelerating velocity. Thresholds were raised in the patient group in both conditions. The loss of the VOR per se cannot explain raised thresholds in the body-stationary condition nor during whole-body (horizontal) oscillation with vertical grating motion. Findings indicate changes in visual processing that make LDS less sensitive to visual motion. It is postulated that these changes are due to adaptive mechanisms involved to reduce oscillopsia. [Copyright &y& Elsevier]

Young fish (Oreochromis mossambicus) were exposed to microgravity (μg) for 9 to 10 days, or to hypergravity (hg) for 9 days. For several weeks after termination of μg and hg, the roll-induced static vestibuloocular reflex (rVOR) was recorded. In stage SHAPE="SOL" ALIGN="C" STYLE="S">1112-fish, the rVOR amplitude (angle between the maximal up and down movement of an eye during a complete 360° lateral roll) of μg-animals increased significantly by 25% compared to 1g-controls during the first post-flight week but decreased to the control level during the second post-flight week. Microgravity had no effect in stage SHAPE="SOL" ALIGN="C" STYLE="S">1416 fish on the rVOR amplitude. After 3g-exposure, the rVOR amplitude was significantly reduced for both groups compared to their 1g-controls. Readaptation to 1g-condition was completed during the second post-3g week. We postulate a critical period during which the development of the macular vestibuloocular reflex depends on gravitational input, and which is limited by the first appearence of the rVOR. At this period of early development, exposure to microgravity sensitizes the vestibular system while hypergravity desensitizes it. [Copyright &y& Elsevier]

Pathogenic variants in AIMP1 gene are rare causes of neurologic disorders. Homozygous frameshift and nonsense variants in AIMP1 have been described in severe neurodegenerative disease. This is the third report of a homozygous nonsense variant in AIMP1 [c.115 C > T (p.Gln39*)] in a girl with severe neonatal onset epileptic encephalopathy. Like the two other cases reported, our patient is also of Filipino descent. Clinical features include microcephaly, poor visual motor development, shallow breathing, severe hypertonia in extremities, severe global developmental delay, poor gag and suck reflex, failure to thrive in the neonatal period, and early onset intractable seizures. Brain MRI showed hypoplasia of corpus callosum as well as cerebellar vermis, global volume loss and diminished myelination for her age. Electroencephalogram at four months of age showed background consisting of synchronous and asynchronous intervals of burst suppression with intermittent multifocal spikes predominantly in the bi-temporal region, suggestive of Early Onset Epileptic Encephalopathy with Burst Suppression (EOEE-BS) which has not been previously associated with the c.115 C > T variant in AIMP1. Of note, she presented to us in super refractory status epilepticus which was eventually controlled after administration of ketogenic diet and Epidiolex (cannabidiol). This report expands the genetic landscape of EOEE-BS. This is the first case of this specific variant in which Epidiolex was administered, which along with Ketogenic diet aided in controlling patient's super refractory status epilepticus. [ABSTRACT FROM AUTHOR]