Dissertations / Theses on the topic 'Vestibulo-Ocular Reflex'
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Sehizadeh, Mina. "Monocular Adaptation of Vestibulo-Ocular Reflex (VOR)." Thesis, University of Waterloo, 2005. http://hdl.handle.net/10012/1247.
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Purpose: This study asks whether active horizontal angular Vestibulo-Ocular Reflex (VOR) gain is capable of monocular adaptation after 4 hours of wearing 10 dioptres (D) of induced anisometropia in healthy human adults. Method: The participants (average age 28 years) wore a contact lenses/spectacles combination for 4 hours. The power of the spectacle was +5. 00D (magnified images 8. 65%) in front of the right eye and ?5. 00D (minified images 5. 48%) for the left eye, while the power of the contact lenses was equal to the subjects? habitual correction, summed with the opposite power of the spectacle lens. Eye and head position data was collected in complete darkness, in one-minute trials before adaptation and every 30 minutes for 2 hours after adaptation. Eye and head position data obtained using a video-based eye tracking system, was analyzed offline using Fast Fourier Transform in MATHCADTM 11. 1 software to calculate VOR gain. The VOR gain was compared between the right eyes and left eyes for the trials before and after adaptation. Results: In the first post-adaptation trial, a significant decrease in VOR gain (? 6%) occurred in the left eye in response to the miniaturizing lens. The right eye VOR gain did not show a significant change in the first post-adaptation trial (?2% decrease). During the remaining trials in the 2 hour follow-up time, both eyes showed a significant decrease compared to the baseline trial. This might indicate habituation of the VOR from repeated testing, or fatigue. Conclusion: There was monocular adaptation of VOR in response to the combined contact lenses/spectacles, but it was not complete and it was not as we expected. However, trying different amounts of anisometropia in one or two directions, a longer adaptation period (more than 4 hours) or monitoring the gain for more than 2 hours after adaptation with a longer separation between trials, might show different results.
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Musallam, Wissam. "A model for the translational vestibulo-ocular reflex." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape16/PQDD_0008/MQ29347.pdf.
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Sekirnjak, Christian. "Intrinsic firing dynamics of identified vestibulo-ocular reflex neurons /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2003. http://wwwlib.umi.com/cr/ucsd/fullcit?p3091340.
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Liao, Ke. "Vestibulo-Ocular Responses to Vertical Translation." Case Western Reserve University School of Graduate Studies / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=case1213822052.
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Musallam, Sam. "Nonlinearity and signal processing in vestibulo-only cells and the translational vestibulo-ocular reflex." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/NQ63768.pdf.
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Meulenbroeks, Anja. "The vestibulo-ocular reflex (VOR) during high-frequency head rotation." [Maastricht : Maastricht : Universiteit Maastricht] ; University Library, Maastricht University [Host], 1997. http://arno.unimaas.nl/show.cgi?fid=5830.
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Feran, Michele T. "Adaptive modulation of visual control over cat vestibulo-ocular reflex." Thesis, McGill University, 1987. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=63761.
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Wearne, Susan. "Spatial orientation of the human linear and angular vestibulo-ocular reflexes during centrifugation." Thesis, The University of Sydney, 1993. https://hdl.handle.net/2123/26488.
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Six independent co-ordinates comprising three rotational and three translational degrees of freedom are required to specify the orientation and motion of a body in inertial space without ambiguity. The vestibular sensors of the inner ear are designed to provide the organism with precisely this information: three approximately orthogonal semicircular canals and two otoliths (utricle and saccule) on either side of the head transduce the three angular and three linear degrees of freedom, respectively. Activation of either angular or linear vestibular sensors results in compensatory reflexes including an angular VOR (AVOR), various linear VOR's (LVOR's) and the vestibulo-spinal reflexes which mediate static and dynamic postural control. The combined input from the vestibular labyrinth thus serves to orient the body and stabilise the eyes during head movement in any spatial plane.
The vestibular sensors are not tied to any particular muscle group; they drive a number of motor systems with disparate physical requirements and functions. How this brainstem system accurately and reflexively partials out the relevant information in the source signal to drive a particular compensatory reflex is the subject of several different sensory-motor modelling approaches. Recent evidence suggests that, analogous to a modern inertial guidance system, the vestibular system uses frequency-selective filtering, realised in the physical properties of the endorgan, and the hair cell receptors, to effect the appropriate channelling.
Considerable interspecies variation in the frequency response of the VCR reflects the range of natural movements of different animals. Analogously, variation in the working ranges of different body movements within a species should be reflected in differential frequency-tuning of the various vestibule-ocular and vestibule-spinal reflexes. Evidence for frequency-selective filtering of all vestibulo-ocular reflexes is presented in the following chapters, and a case developed for a peripheral filtering system which generates appropriate canal-ocular and otolith-ocular reflexes during combined, often ambiguous linear and angular acceleration stimulation.
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Lundberg, Simon. "Evaluation of a Motion Simulation Platform for Vestibulo-Ocular Research." Thesis, KTH, Skolan för teknik och hälsa (STH), 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-149876.
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The vestibuloocular reflex can be manually elicited by tilting or rotating the head. Manual techniques serve their purpose well and is the golden standard in the clinical work, but they lack control of velocity and movement pattern. However, motion simulation platforms enable automatic control of both velocity and movement pattern. One motion simulation platform, named BIRGIT, has been built at the Department of Clinical Neurosciences at Karolinska Institutet but has not yet been in service and require a performance evaluation. The objectives with this thesis is to evaluate the accuracy and precision of BIRGIT and evaluate how bodyweight and movement direction impact the performance. The thesis also evaluate whether it is possible to stabilize the head of the patient during the acceleration phase. Repeated measurements of acceleration with different loads, desired ac- celeration, direction and motion type (rotational and translational), are per- formed. Dummies are used to simulate bodyweight in the performance study and real persons are used in the head stabilization study. Analysis of variance (ANOVA) is the main statistical tool. The results suggest that the platform does not perform equally at dif- ferent load or directions and that there is a bias between desired and true acceleration. The main problems are an inclination of the rails, upon which the chair is mounted, that causes differences between directions and an un- desirable performance characteristic for rotational motions. The stabilization study suggest that the head can be stabilized.Den vestibulo-okul ̈ara reflexen kan framkallas genom att manuellt rotera eller rycka p ̊a huvudet. Att manuellt framkalla reflexen fungerar i de flesta sam- manhang va ̈l och a ̈r standard i m ̊anga underso ̈kningar. Dock g ̊ar det inte att till fullo kontrollera vare sig hastighet eller ro ̈relsebana perfekt. Emellertid g ̊ar detta att kontrollera genom att anva ̈nda sig av en s ̊a kallad ro ̈relsesimu- leringsplatform. En s ̊adan platform, d ̈opt till BIRGIT, har byggts vid Institutionen f ̈or kliniska neurovetenskaper vid Karolinska Institutet. Denna har ej bo ̈rjat anva ̈ndas ̈annu d ̊a dess prestanda fo ̈rst beho ̈ver utv ̈arderas. Syftet med denna uppsats ̈ar att utva ̈rdera precision och noggrannhet hos BIRGIT. Dessutom, att utv ̈ardera hur kroppsvikt och ro ̈relseriktning inverkar p ̊a prestandan. I arbetet ing ̊ar ̈aven att testa om det a ̈r m ̈ojligt att stabilisera huvudet under accelerationsfasen. Repeterade ma ̈tningar av sann acceleration med olika last, riktning, bo ̈rac- celeration och r ̈orelsetyp (rotation eller sidledes) genomfo ̈rdes. Testdockor anva ̈ndes fo ̈r att simulera lasten i prestandatesterna och riktiga testpersoner anva ̈ndes i huvudstabiliseringsdelen. Variansanalys (ANOVA) var det hu- vudsakliga statistiska verktyget. Resultatet antyder att last och ro ̈relseriktning inverkar p ̊a acceleratio- nen och prestandan och att den sanna accelerationen alltigenom a ̈r la ̈gre a ̈n bo ̈raccelerationen. Det finns tv ̊a sto ̈rre problem hos plattformen, det fo ̈rsta a ̈r att uppha ̈ngningen till stolen lutar och detta resulterar i en skillnad mellan riktningarna (det g ̊ar fortare nedf ̈ors). Det andra problemet a ̈r ett cykliskt uppfo ̈rande na ̈r flera rotationsr ̈orelser skall fo ̈lja p ̊a varandra. Stabiliseringsstudien visade att det g ̊ar att stabilisera huvudet.
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Khojasteh-Lakelayeh, Elham. "Modeling fixation-distance-related modulations in the vestibulo-ocular reflex (VOR)." Thesis, McGill University, 2003. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=79238.
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The vestibulo-ocular reflex (VOR) serves to stabilize retinal images of targets during head angular and/or linear displacements by moving the eyes at an appropriate speed and in a direction that compensates for head movements. Contrary to traditional understandings, we now know that the VOR function is not hard-wired; rather it is deeply modified by the context in which eye movements occur. Among these contexts, the fixation context is the main focus of this thesis. It has been proven, both experimentally and through geometric relationships, that the VOR gain (the ratio of eye velocity to head velocity) modulates with fixation distance. Furthermore, depending on the target distance from each eye, the VOR gain can be different for each eye. We present a bilateral model that accounts for VOR response modulations with fixation distance and is also compatible with anatomical and physiological facts.All the previous models that have been proposed for viewing-distance-related VOR response modulations use black-box mathematical representations to modulate the reflex, providing no insight into the underlying anatomy and physiology. This thesis is an attempt to show that VOR fixation-distance-dependent modifications can be achieved automatically through the physiological characteristics of the second-order neurons in the vestibular nuclei (VN), without having to apply any specific vergence encoding signals. The model presented here relies on the nonlinear behavior of the specific cells in the VN, which has been observed in prior experimental studies. The model reproduces the VOR gain that is observed at different vergence levels. It also allows for modifications in VOR dynamics by applying changes to the sensitivities of the VN cells that lie within the system loops.
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Burcham, Marc A. "Suppression of the Rotational Vestibulo-Ocular Reflex during a Baseball Pitch." The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1275390727.
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Diehl, Mark D. "Visual Contributions to the Vestibulo-Ocular Reflex during Balance Recovery Tasks." VCU Scholars Compass, 2007. https://scholarscompass.vcu.edu/etd/1429.
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Introduction: The Vestibulo-ocular reflex (VOR) is quantified by computing the ratio of head angular velocity and eye angular velocity (VOR Gain). This measure only includes head angular movements; linear translations are not accounted for. These investigations postulate an alternative method of VOR quantification, one that assesses retinal image stability during head angular and linear movements (Foveal fixation (FF)). This method was used to assess the role of vision in balance reactions. Methods: Experiment 1 : Ten Young subjects were fitted with an eye tracker linked to an EM kinematic recording system. This allowed for the recording of head, trunk and eye kinematics during the performance of gaze stabilization tasks. Subjects fixated an LED target while performing head flexion and extension exercises at four frequencies. Point-of-gaze analysis was performed by transforming eye-in-head and head-in-space data into eye-in-space data, which were compared to the known location of the targets. The distance between the eye vector target plane intersection and the target location provided an error that could be used to calculate the estimated image location on the retina. FF and VOR gain were compared with head angular velocities to determine correlations. Experiment 2: Balance was assessed in Young and Elderly following a series of perturbations. Dependent variables included: step latency, head and trunk angular velocity, VOR Gain, FF. Results: Correlations between head angular velocity and FF showed that retinal image stability degraded as head angular velocity increased. Elderly showed a more rapid degradation of FF with higher overall head angular velocities. Comparisons between rate of change of VOR and FF over velocity spectrum indicated a greater change in FF response. A negative linear correlation between FF and Step Latency was observed: there was no relationship between VOR gain and Step Latency. Conclusion: FF is a more sensitive measure of VOR than Gain as it accounts for angular and translational head movements. Its correlation with Step Latency suggests the importance of image stability in formulating responses following perturbation.
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McGuinness, James. "Implications of potassium channel heterogeneity for model vestibulo-ocular reflex response fidelity." Thesis, University of Stirling, 2014. http://hdl.handle.net/1893/21844.
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The Vestibulo-Ocular Reflex (VOR) produces compensatory eye movements in response to head and body rotations movements, over a wide range of frequencies and in a variety of dimensions. The individual components of the VOR are separated into parallel pathways, each dealing with rotations or movements in individual planes or axes. The Horizontal VOR (hVOR) compensates for eye movements in the Horizontal plane, and comprises a linear and non-linear pathway. The linear pathway of the hVOR provides fast and accurate compensation for rotations, the response being produced through 3-neuron arc, producing a direct translation of detected head velocity to compensatory eye velocity. However, single neurons involved in the middle stage of this 3-neuron arc cannot account for the wide frequency over which the reflex compensates, and the response is produced through the population response of the Medial Vestibular Nucleus (MVN) neurons involved. Population Heterogeneity likely plays a role in the production of high fidelity population response, especially for high frequency rotations. Here we present evidence that, in populations of bio-physical compartmental models of the MVN neurons involved, Heterogeneity across the population, in the form of diverse spontaneous firing rates, improves the response fidelity of the population over Homogeneous populations. Further, we show that the specific intrinsic membrane properties that give rise to this Heterogeneity may be the diversity of certain slow voltage activated Potassium conductances of the neurons. We show that Heterogeneous populations perform significantly better than Homogeneous populations, for a wide range of input amplitudes and frequencies, producing a much higher fidelity response. We propose that variance of Potassium conductances provides a plausible biological means by which Heterogeneity arises, and that the Heterogeneity plays an important functional role in MVN neuron population responses. We discuss our findings in relation to the specific mechanism of Desynchronisation through which the benfits of Heterogeneity may arise, and place those findings in the context of previous work on Heterogeneity both in general neural processing, and the VOR in particular. Interesting findings regarding the emergence of phase leads are also discussed, as well as suggestions for future work, looking further at Heterogeneity of MVN neuron populations.
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Huebner, William Paul. "Cancellation of the vestibulo-ocular reflex during horizontal combined eye-head tracking." Case Western Reserve University School of Graduate Studies / OhioLINK, 1991. http://rave.ohiolink.edu/etdc/view?acc_num=case1055363590.
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Coenen, Olivier J. M. D. "Modeling the vestibulo-ocular reflex and the cerebellum : analytical & computational approaches /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC IP addresses, 1999. http://wwwlib.umi.com/cr/ucsd/fullcit?p9935445.
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Murnane, Owen D., Kristal M. Riska, Stephanie Rouse, and Faith W. Akin. "Inter-ocular Gain Differences of The Horizontal Vestibulo-ocular Reflex During the Video Head Impulse Test." Digital Commons @ East Tennessee State University, 2015. https://dc.etsu.edu/etsu-works/1870.
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Zhang, Keqin 1962. "Exploring fast phases of the vestibulo-ocular reflex as indicators of vestibular lesion." Thesis, McGill University, 1995. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=23761.
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This thesis investigates the dynamic characteristics of fast phase eye movements in the Vestibulo-Ocular Reflex (VOR) and their application in vestibular lesion clinics. Eye responses in the VOR consist of alternations between slow phases (eye moves opposite to head) to stablize the eye in space and fast phases to quickly redirect the eye in space. At the end of each fast phase segment, the eye position appears well correlated with head velocity. In contrast to slow phases, fast phases are of quite short duration. Therefore, they must be detected precisely in order to do any further analysis. This thesis reports an improved version of a previous autoregression (ARX) model classification algorithm, to allow automatic classification of fast phase segments or to detect only end points of fast phases.Results in this thesis demonstrate that the dynamics associated with the fast phase end points present specific patterns. These patterns can be represented as a linear or a cubic equation. In other words, a first-order or third-order polynomial can be fitted to the experimental data by the least square technique. The DC bias of the fitted data shows distinctive ranges for normal subjects and vestibular lesion patients. The asymmetric an non-linear shapes of the fitted curve can also denote a lesion. Other dynamic properties, such as the fast phase segment frequencies or the phase shift between the output eye position and input head velocity, have strong tendencies to differentiate normals from patients. In addition, the characteristics of fast phase beginning points suggest that the initiation of fast phases in independent of any obvious eye velocity or eye position threshold.
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LI, QI. "Development and Proof of Concept of a Vestibulo-Ocular reflex Rehabilitation Video Game." Case Western Reserve University School of Graduate Studies / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=case1607590770501539.
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Draper, Mark. "The adaptive effects of virtual interfaces : the vestibulo-ocular reflex and simulator sickness /." Thesis, Connect to this title online; UW restricted, 1998. http://hdl.handle.net/1773/7069.
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Cox, Michele Margaret Freedman William McElligott James G. "The effects of a neurosteroid, pregnenolone sulfate, in the cerebellum on vestibulo-ocular reflex adaptation (VOR) in goldfish /." Philadelphia, Pa. : Drexel University, 2006. http://hdl.handle.net/1860/1119.
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Magnusson, Anna K. "Central vestibular compensation : the role of the GABA B receptor /." Linköping : Univ, 2002. http://www.bibl.liu.se/liupubl/disp/disp2003/med765s.pdf.
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Kam-Thong, Tony. "Fast phase components of the vestibulo ocular reflex: segment classification and transient system identification." Thesis, McGill University, 2008. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=18730.
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This thesis investigates the dynamic characteristics of the Vestibulo-Ocular Reflex (VOR) in particular the rapid components of eye movements induced by head rotations in the horizontal plane. The VOR is a reflex eye movement that serves to provide a stabilized perception of the external environment in response to head movement. The reflex originates in the vestibular sensors in both inner ears, in particular the semicircular canals for the angular VOR. The afferent sensory signals eventually drive the appropriate eye movements by sending motoneural signals to the eye plant(s). The VOR response consists of alternating slow phase and fast phase modes of operation. During slow phases, the eye velocity acts in a compensatory direction to the head stimulus to maintain a constant perception of the outside world. During fast phases, there is a sudden short-duration spike in eye velocity in the same direction as the head velocity. The eye then acts in the anti-compensatory direction to minimize the error signal noted between a stored efferent eye position and the intended target extracted from the vestibular signal. This thesis reports on improved model fitting performance and physiological relevance in the analysis of VOR characteristics. In particular, it uses transient system identification in contrast to traditional end point envelopes for the detection of VOR fast phase dynamics. This required the implementation of an automated model complexity selection scheme, based on Null-Hypothesis and Akaike criteria to allow for any combination of coefficients in a non-linear representation with up to third order polynomials. Identification results are compared for cases using either all, rightwards-only or leftwards-only fast phase segments. The results support implications from physiology, in that the fast phase mechanism is predominantly unilateral with respect to motion sensors. Moreover, the estimated non-linear characteristics and dynamics of the fast phase mCe mémoire étudie les caractéristiques dynamiques des mouvements de l'œil en particulier les composants rapides du Réflexe Vestibulo-Oculaire (RVO) induits par les rotations de la tête sur le plan horizontal. Le RVO est un mouvement réflexe de l'œil qui sert à fournir une perception stabilisée de l'environnement externe en réponse au mouvement de la tête. Le réflexe commence aux canaux semi-circulaires, organes sensorielles de l'accélération angulaire situés dans les deux oreilles externes. Les signaux sensoriels afférents conduisent par la suite les mouvements appropriés d'oeil en envoyant des signaux motoneurals aux muscles oculaires. La réponse RVO se compose d'une alternation entre la phase lente et la phase rapide. Pendant les phases lentes, la vitesse des mouvements de l'œil agit dans une direction compensatoire au stimulus, principalement pour maintenir une perception constante du monde externe. Durant les phases rapides, il y a une transition soudaine de courte durée de la vitesse de l'œil dans la même direction que celle de la tête. L'œil agit alors dans la direction anti-compensatoire pour réduire au minimum le signal d'erreur entre une position efférente de l'œil enregistrée et le point prévu de la cible prévue extraite à partir du signal vestibulaire. Cette thèse présente un modèle ayant une performance améliorée et une meilleure acuité physiologique dans l'analyse des caractéristiques de RVO En particulier, elle emploie l'identification du système transitoire contrairement aux enveloppes traditionnelles de point final pour la détection de la dynamique de la phase rapide du RVO. Ceci a exigé l'exécution d'un arrangement modèle automatisé de choix de complexité, basée sur des critères de Nul-Hypothèse et d'Akaike pour tenir compte de n'importe quelle combinaison des coefficients dans une représentation non linéaire avec des polynômes de troisième ordre. Trois modèles de la phase rapide ont été
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Kulbaski, Mark John. "Effects of weightlessness on the vestibulo-ocular reflex in the crew of Spacelab 1." Thesis, Massachusetts Institute of Technology, 1986. http://hdl.handle.net/1721.1/83661.
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Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1986.MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING
Bibliography: leaf 92.
by Mark John Kulbaski.
B.S.
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Fajardo, Ann B. "Does vergence influence the vestibulo-ocular reflex in human subjects rotating in the dark?" Thesis, This resource online, 1996. http://scholar.lib.vt.edu/theses/available/etd-12172008-063057/.
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Rogers, Stephen John. "'VOR' - an interactive iPad model of the combined angular and linear vestibulo-ocular reflex." Thesis, The University of Sydney, 2014. http://hdl.handle.net/2123/13536.
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The mammalian vestibular system consists of a series of sensory organs located in the labyrinths of the inner ear that are sensitive to angular and linear movements of the head. Afferent inputs from the vestibular end organs contribute to balance, proprioception and vision. The vestibulo-ocular reflex (VOR) driven by these sensory inputs produces oculomotor responses in a direction opposite to head movement which tend to stabilise visual images on the retina. We present a model, in the form of a software application called VOR, which represents a simplified view of this complex system. The basis for our model is the hypothesis that afferent vestibular signals are integrated to maintain a notional internal representation of the head position (RHP). The vestibulo-ocular reflex maintains gaze towards a world-fixed point relative to the RHP, regardless of the actual head position. The RHP will imperfectly match the real head position when end organ input imperfectly reports head movements, such as can occur in cases of organ dysfunction and even in healthy subjects due to adaptation to motion stimuli. We do not claim that any specific observable part of the real vestibulo-ocular system corresponds to the RHP, but it seems reasonable to suggest that it might exist as a literal "neural network", trained through evolution and experience to maintain gaze during head movement. We hypothesise that the real VOR is supported by this internal representation, continually updated by afferent signals from the vestibular end organs, and that VOR eye responses tend to direct the eyes towards a fixed point in the world. Human vestibulo-ocular research typically employs equipment to which a subject is securely attached and allows rotation around, and sometimes linear movement along, one or more axes ("rotating chair") while attempting to maintain gaze on a fixation point, fixed relative to the head or world. A series of consecutive movements are referred to as a "motion profile". Meanwhile eye movements are recorded, using scleral search coils (or, more recently, video cameras and image-processing software) which can detect the horizontal, vertical and torsional components of the direction of each eye. VOR allows the user to define motion profiles and predicts the eye movements that a researcher or clinician might expect to observe in a real subject during such motion profiles. For example, the "on-centre rotation" motion profile specifies that the subject's head is positioned upright and centred around the vertical axis of the rotating chair, with a chair-fixed fixation point 1m in front of the subject. The chair accelerates angularly to 200°/sec over 20 seconds, rotates at a constant 200°/sec for 60 seconds, then decelerates to stationary over 20 seconds. The model accurately predicts the transient nystagmus that would be expected: its direction, duration, phase velocity and even the brief secondary nystagmus which is characteristic of adaptation to constant velocity rotation. VOR also allows the user to define end organ condition configurations, e.g. "normal", "bilateral vestibular loss", "unilateral superior neuritis", which are represented as a series of response gains attached to the sensory inputs from each end organ, relative to a nominal perfect gain of 1, and various other parameters which are derived from the human vestibular system, including the rate of drift of gaze to fixation point in light and dark, the rate at which the end organs adapt to constant stimuli, and quick-phase trigger dependencies. The VOR is not the only source of eye movement while attempting to maintain gaze on a fixation point. In our model, eye position drifts towards the fixation point at a nominal fixed rate. If this slow drift is insufficient to maintain gaze on the fixation point, a saccade or quick phase is triggered. Hence the transduction of mechanical forces at the labyrinths into sensory signals, subject to end organ conditions and adaptation that reduce the strength of the neuronal signals, maintain the RHP. Eye movement is then determined entirely by (a) the direction from RHP to the (world-referenced) fixation point, and (b) the disparity between eye direction and actual fixation point (which may be head-referenced). To validate the model, we prepared 24 motion profile/end organ condition combinations, compared the outputs from our model with real world observations, and found the results to be similar. Similarities include a simple first approximation of the linear and angular VOR; nystagmus caused by a subject's attempts to maintain fixation on a head-referenced target during head movement; decay of nystagmus through adaptation to stimulus, including secondary nystagmus; indefinitely prolonged nystagmus during off-vertical axis rotation (OVAR); rapid decay of nystagmus during the "tilt dump" motion profile, and dynamic cyclovergence during vertical linear acceleration. VOR is programmed in Objective-C using Xcode and runs on the Apple iPad. Its screen displays a 3d graphical representation of the virtual subject's head and eyes, including imaginary lines of sight to clarify eye movements. The user may program an effectively unlimited series of linear and angular motions of the rotating chair, and of the virtual subject's head relative to the chair. They may also program the gain (roughly, the sensitivity) associated with each end organ and other variables relating to the subject. They may select a series of internal variables to chart during the motion profile such as head velocity, eye direction, neuron firing rates, etc., while simultaneously displaying the head and eyes. VOR can record a video screen capture of the virtual head, eyes and lines of sight during the execution of a motion profile, a CSV file containing the internal variables at each time interval, a PNG image of the labelled chart, PDF descriptions of the motion profile and end organ condition configurations, and data files defining the motion profiles and end organ conditions which can then be exchanged between researchers/clinicians. Predefined motion profiles include: lateral, LARP and RALP head impulses; lateral head impulse with close fixation point; sinusoidal yaw, on-centre rotation, linear heave along Y axis, linear oscillation along X, Y and Z axes; linear sled along Y axis; forward- and backward-facing centrifugation; off-vertical axis rotation; tilt dump; and head tilt. Predefined conditions include: normal; left unilateral vestibular loss; bilateral vestibular loss; left superior neuritis; and "perfect" (unrealistic gain of 1 in otoliths, producing perfect linear VOR). All of these motion profiles and conditions may easily be modified, created and shared.
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Johnson, Erika L. "Computerized Dynamic Visual Acuity with Volitional Head Movement in Patients with Vestibular Dysfunction." Scholar Commons, 2002. https://scholarcommons.usf.edu/etd/1521.
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Patients with non-compensated vestibular dysfunction frequently complain of the ability to maintain dynamic visual acuity during activities which require the movement of the head. When this occurs the patient is experiencing oscillopsia, which is the symptom resulting from a non-functional vestibulo-ocular reflex (VOR). To measure the presence of oscillopsia, tests of dynamic visual acuity (DVA) may be used.
A recent test of DVA has been reported which is administered while patients are walking on a treadmill. Although this test has been shown to be useful in evaluating DVA in patients, there are several disadvantages to treadmill use. These include physical space, cost and accessibility. Additionally, walking at the required treadmill speed to produce sufficient head movement may pose difficulties and be medically contraindicated for patients with certain health risks. The purpose of this study was to evaluate a different method to measure DVA in patients which would not require the use of the treadmill, but instead utilize a volitional head movement to reveal oscillopsia. In this study, patients performed the DVA test in two conditions: (1) walking on a treadmill, and (2) seated on a chair volitionally moving the head.
In this study, DVA was tested in both conditions with 15 adults with normal vestibular function, and 16 adults with vestibular impairment. Results revealed that both methods, treadmill walking and volitional head movement, appeared equivalent for measuring DVA in normal subjects and vestibular impaired subjects. The lack of finding a significant main effect of method, and interactions that include method, supports the equivalence of volitional head movement to a treadmill approach for the measurement of DVA.
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Walter, Gillian. "An anatomically relevant model of central processing in the 3D slow-phase vestibulo-ocular reflex." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape3/PQDD_0029/MQ64252.pdf.
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Chan, Wai Pang Wilbur. "A set-point dependent nonlinear model for the Neural Integrator in the Vestibulo-Ocular Reflex." Thesis, McGill University, 2009. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=32249.
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The Neural Integrator (NI) in the oculomotor system is a conceptual process presumed to perform mathematical integration of eye velocity related sensory signals into motor signals controlling ocular orientation (position) in the orbit. It participates in tasks such as maintaining gaze in space during head fixed or head-free viewing of targets. The NI is classically assumed to perform ideally (large time constants) and to be identical in all tasks. This thesis explores past assumptions on the time-invariant characteristics of the NI. During passive head movement in the dark and measurements of the horizontal Vestibulo-Ocular Reflex (VOR), the dynamics of the NI were found to vary dynamically, depending on head velocity and eye positional set-points. To investigate the observed phenomenon, we incorporated a nonlinear component into an existing model for the NI and attempted to emulate the context-dependent changes in the NI dynamics. To estimate the model parameters, optimization methods were used instead of the least squared based algorithms due to the more complex formulation of the nonlinear NI model. When comparing nonlinear NI model estimates during passive VOR responses in human subjects, the nonlinear parameters were found to differ greatly between vestibular patients and the control group; furthermore, the nonlinear model predicts apparent NI dynamics that are set-point dependent for most of the subjects, even in controls. The form and optimal set-point for the NI characteristics are well correlated with the side of a lesion in patients, even after compensation. Furthermore, the non-linear NI formulation provides better fits on ocular data, than the presumed ideaL'intégrateur neural (IN) dans le système oculomoteur est un processus conceptuel présumé d'effectuer l'intégration mathématique des signaux sensoriels relatifs à la vitesse de l'oeil en signaux moteurs commandant l'orientation oculaire (position de l'oeil) dans l'orbite. L'IN participe aux tâches telles que maintenir le regard dans l'espace pendant le visionnement des cibles à tête fixe ou libre. Classiquement, l'IN est supposé intégrer idéalement (avec de grandes constantes de temps) et identiquement dans toutes les tâches. Cette thèse explore les anciennes prétentions sur les caractéristiques temps-invariables de l'IN. Durant le mouvement passif de la tête dans l'obscurité et en mesurant le réflexe Vestibulo-Oculaire (RVO) horizontal, la dynamique de l'IN s'est avérée de varier dynamiquement, selon la vitesse de la tête et les points de consigne de la position de l'œil. Pour étudier le phénomène observé, nous avons incorporé un composant non linéaire à un modèle existant de l'IN et nous avons essayé d'émuler les changements contexte-dépendants dans les dynamiques de l'IN. Pour estimer les paramètres du modèle, des méthodes d'optimisation ont été employées au lieu des algorithmes basés sur le moindre carré à cause de la formulation plus complexe du modèle non linéaire de l'IN. En comparant des évaluations non linéaires du modèle pendant des RVO passives chez des sujets humains, on a trouvé que les paramètres non linéaires diffèrent considérablement entre les patients vestibulaires et le groupe de control; de plus, le modèle non linéaire prévoit les dynamiques apparentes de l'IN qui dépendent de la point de con
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Walter, Gillian. "An anatomically relevant model of central processing in the 3D slow-phase vestibulo-ocular reflex /." Thesis, McGill University, 1999. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=30276.
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A bilateral model of central processing in the 3D slow-phase vestibulo-ocular reflex (VOR) has been developed. Two possible implementations of the model have been examined, one placing required nonlinearities in a feedforward pathway and the other using an additional feedback path instead. The behaviour of the two forms was investigated for parameter variation and under artificial lesion conditions. A literature review was conducted to propose an anatomical substrate for the model and possible sites for required cross-talk between the horizontal and vertical/torsional pathways. Neural network models of the VOR and oculomotor integrator were reviewed and discussed. A neural network simulation was presented to illustrate how simple thresholding and saturation of neuron responses may aid in generating the proposed nonlinearities without separate specialized computing stages.
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Sienko, Kathleen Helen 1976. "Artificial gravity : adaptation of the vestibulo-ocular reflex to head movements during short-radius centrifugation." Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/9237.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2000.Also available online at the MIT Theses Online homepage
Includes bibliographical references (p. 89-93).
Short-radius centrifugation is currently being pursued as a potential countermeasure to long duration space flight. Short-radius centrifugation requires relatively high angular velocities (on the order of 30 rpm) to create centripetal accelerations on the order of 1 g. Unfortunately, out-of-plane head movements during centrifugation induce inappropriate vestibulo-ocular reflexes, debilitating motion sickness symptoms, and illusory tilt sensations due to conflicting visual and vestibular signals. Practical use of an intermittent short-radius centrifuge as a countermeasure requires that crew members be capable of rapidly adapting to the unexpected semicircular canal inputs with minimal side- or post-effects. Furthermore, adaptation not only has to be achieved, it also has to be appropriate for the environment (stationary, rotating, 1 g, or 0 g). The purpose of this research was to investigate humans' ability to attain and maintain adaptation to rotating environments. Subjects participated in a series of pre-/per-/and post-rotation data collection sessions consisting of both eye reflex recordings during head movements, a subjective battery of tests, and autonomic measurements. Eight subjects were tested on three days (D=1, 2, 8). Eye movements were measured in response to out-of-plane head movements during rotation at 23 rpm on-board the MIT short-radius centrifuge (r=2 m). Slow phase eye velocity (SPV) was reconstructed from filtered and de-saccaded eye movement data. The significant main effect of day and pre-/post-adaptation phase demonstrated that normalized SPV decreased following adaptation in the light.
by Kathleen Helen Sienko.
S.M.
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Hong, Juimiin. "Modification of the disynaptic vestibulo-ocular reflex pathway after a unilateral canal plug in the cat." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape10/PQDD_0024/MQ40865.pdf.
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Huterer, Marko. "Characterization of vestibulo-ocular reflex dynamics : responses to head perturbations during gaze stabilization versus gaze redirection." Thesis, McGill University, 2001. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=33004.
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In this study, we compare VOR response dynamics induced by high-frequency (>5 Hz) passive head-on-body perturbations, applied during gaze stabilization versus gaze redirection. During gaze stabilization, we first rotated the heads of three Rhesus monkeys over the frequency range 5--25 Hz. The VOR was compensatory across all frequencies tested; mean gains (eye velocity/head velocity) were near unity, with phase lag increasing only slightly with frequency. Transient perturbations ≥80 Hz were then used to further probe VOR dynamics. During periods of gaze stabilization, VOR response latency to the transient perturbations was 5--6 ms, and mean gain induced was near unity for two of the three animals tested. The same perturbations were then applied at different intervals before, during and following 15°, 40° and 60° gaze shifts. The VOR elicited was generally attenuated compared to that evoked during gaze stabilization, and the level of suppression tended to decrease with time from gaze shift onset. We conclude that models for the control of gaze should be modified to account for the time course of VOR gain changes during gaze shifts.
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Brown, Daniel A. "The Relationship Between Concussion Symptoms and Vestibulo-Ocular and Cervical Spine Function in Combat Sport Athletes." Thesis, Griffith University, 2022. http://hdl.handle.net/10072/419978.
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Background: Concussion is a growing concern for athletes who participate in combat sport. Many rule sets allow for intentional and repeated forceful strikes to the head that may result in a concussion. The forceful impacts to the head may lead to impairments in the vestibulo-ocular system and cervical spine complex which can negatively impact athletic performance. Symptoms that are often associated with concussion may be related to deficits in the vestibulo-ocular system or cervical spine complex. Thus, it is important to consider the vestibulo-ocular system and cervical spine complex when assessing and treating an athlete involved in combat sports with a suspected concussion. However, very few studies have explored the prevalence of symptoms associated with concussion or the function of the vestibulo-ocular system and cervical spine complex in athletes involved in combat sports.
Objectives: The first aim of this thesis was to investigate the prevalence of concussion-related symptoms in adult athletes who participate in combat sports. The second aim was to compare the function of the vestibulo-ocular system and cervical spine complex between combat sport athletes and active control participants. The third aim was to explore relationships between symptom-based outcome measures and vestibulo-ocular system and cervical spine complex function in combat sport athletes.
Methods: Study 1 established the prevalence of concussion-related symptoms using the Post-Concussion Symptom Scale (PCSS) via an online survey of active combat sport athletes (n = 309) and examined relationships between the history of concussion and neck injury with the symptom scores (Chapter 4). Studies 2, 3 and 4 examined differences in the vestibulo-ocular system and cervical spine complex between combat sport athletes (n = 40) and healthy control participants (n = 40). The Vestibular/Ocular Motor Screening (VOMS) assessment (Chapter 5) was used to assess between-group differences in vestibular and oculomotor characteristics. A standardised protocol that assessed: 1) oculomotor function, 2) benign paroxysmal positional vertigo (BPPV), and 3) vestibulo-ocular reflex (VOR) function (Chapter 6) was used to further compare the function of the vestibulo-ocular system between groups. A standardised suite of clinical assessments was conducted to examine the between-group differences in the cervical spine complex (Chapter 7). The PCSS, VOMS, Dizziness Handicap Inventory (DHI) and Neck Disability Index (NDI) were used to explore relationships between symptom-based outcome measures and the function of the vestibulo-ocular system and cervical spine complex.
Results: Study 1 found that over half of active combat sport athletes (59.9%) experienced at least two concussion-related symptoms. Athletes with a history of concussion and neck injury also had significantly greater odds of reporting ‘high’ total symptom and severity scores on the PCSS than athletes who did not report a history of injury. In Studies 2 and 3, athletes who participated in combat sports demonstrated differences in vestibulo-ocular function compared with healthy controls. That is, an abnormal VOMS or NPC score was reported by 45% of the combat sport group compared with 22.5% of the control group. A significantly larger proportion of the combat sport group had oculomotor abnormalities than the control group. There were no differences between groups in the presence of BPPV or in the function of the VOR. Overall, the results indicated that athletes who participated in combat sports had a greater number of vestibulo-ocular impairments than control participants. The results of Study 4 indicated that combat sport athletes had a reduced cervical spine range of motion and greater isometric muscle strength and muscle endurance than the control group. No differences were observed between groups for cervical spine proprioception or segmental tenderness on manual spinal examination. Furthermore, the results identified several significant relationships between the vestibulo-ocular system and cervical spine complex with symptom-based outcome measures.
Conclusion: Concussion-related symptoms were experienced by most active combat sport athletes, with a history of concussion and neck injury increasing the odds of reporting high symptom scores on the PCSS. This thesis demonstrated functional differences in the vestibulo-ocular system and cervical spine complex in combat sport athletes compared with control participants. In addition, the functions of both the vestibulo-ocular system and cervical spine complex were related to several symptom-based outcome scores. The findings highlight the importance of clinicians who care for combat sport athletes to provide a comprehensive multisystem approach when assessing symptoms often attributed to concussions.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Health Sci & Soc Wrk
Griffith Health
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Smith, Heather L. H. "The linearizing properties of a bilateral structure in the vestibulo-ocular reflex : a theoretical and simulation study." Thesis, McGill University, 1988. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=61664.
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Pouliot, Christopher Francis. "Changes in the horizontal angular vestibulo-ocular reflex of SLS-2 space shuttle astronauts due to weightlessness." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/47374.
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Hawkins, Kim Elizabeth. "Vestibular function and vestibulo-visual sensory integration in people with Parkinson’s disease: a comparison with age matched controls." Thesis, University of Sydney, 2021. https://hdl.handle.net/2123/26238.
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Vestibular dysfunction may be a consequence of the neurodegenerative disorder, Parkinson’s disease (PD). Neuropathological studies support this hypothesis, but clinical studies of vestibular reflex testing have conflicting findings. Modern tests, the head impulse test (HIMP), the suppression head impulse test (SHIMP) and bone-conducted ocular and cervical vestibular-evoked myogenic potentials (oVEMPs and cVEMPs), have scarcely been reported in PD. Virtual reality (VR) assessment tools, have not been applied to PD. This prospective observational study compared vestibular function in 40 people with PD to 40 age-matched controls (HC). The study analysed dynamic vestibular reflex function: i) semi-circular canal mediated vestibulo-ocular reflex (VOR) and saccades with HIMP and SHIMP; ii) otolith mediated VOR with oVEMPs, and iii) otolith mediated vestibulo-collic reflex with cVEMPs. VEMPs were induced by both clicks and forehead taps. Static otolithic function was assessed via a VR subjective visual vertical (SVV) test. Vestibulo-visual integration was compared on a VR standing balance protocol. In early to mid-stage PD, VOR gains measured with HIMP and SHIMP were not significantly different from HC. However, in PD, SHIMP peak saccade velocity was reduced (p<.001) and latency prolonged (p=.003). Tap oVEMPs were more robust than clicks in both groups. PD had more absent cVEMP responses to both clicks (p=.03) and taps (p=.002) and more abnormal SVV responses (p=.01) with greater variability (p<.001). PD failed at lower levels of VR visual perturbation on both firm (p=.01) and foam surfaces (p=.001) than HC. Knowledge of vestibular dysfunction in PD will help guide targeted rehabilitation. From these findings, interventions for early to mid PD should focus on sensory integration protocols incorporating head motion.
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Green, Andrea Michelle. "Visual-vestibular interaction in a bilateral model of the rotational and translational vestibulo-ocular reflexes : an investigation of viewing-context-dependent reflex performance." Thesis, McGill University, 2000. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=36810.
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Traditionally, the vestibulo-ocular reflex (VOR) has been considered a stereotyped ocular counterrotation response to head movement that stabilizes a visual image on the retinae. However, during natural head movements, the appropriate magnitudes and directions of compensatory ocular deviations depend on viewing context. Moment-to-moment adjustments in VOR performance are required as gaze is redirected towards different viewing locations.This thesis presents an investigation of viewing-context-dependent VOR performance through the development of a physiologically and anatomically based bilateral model structure. Previous theoretical studies of visual-vestibular interactions during head-centered rotation are extended by simulating both ocular responses and those of individual premotor brainstem neuron types in an integrated binocular controller for slow eye movements. Central sensitivities to vestibular canal signals are modulated as a function of instantaneous binocular fixation state to simulate appropriate viewing-location-dependent changes in monocular rotational VOR performance and distinct premotor cell behaviors.
A new hypothesis for the central dynamic processing of sensory otolith signals in the translational VOR is presented. Previous proposals suggested that the unique dynamic characteristics of otolith and canal afferent signals imply additional central processing in the translational as compared to the rotational VOR pathways. The strategy presented here demonstrates that projecting canal and otolith signals onto a shared premotor circuit at unique sites is sufficient to reproduce observed ocular and central behaviors without introducing additional central filters. By implementing this simple strategy in the bilateral model structure the ability to achieve appropriate compensatory responses for different translation directions and viewing locations in the horizontal plane is demonstrated.
Finally, the model is extended to incorporate brainstem-cerebellar interactions. Current conclusions surrounding potential central sites for plasticity underlying long-term VOR gain adaptation are evaluated. The work makes new suggestions for vestibulo-ocular system organization and proposes directions for experimental work in addressing the following general themes: (1) Sensory convergence onto a shared premotor controller; (2) The role of a bilateral topology in motor pattern selection and binocular coordination; (3) The role of central connectivity in the appearance of distinct premotor cell types; (4) The ability to localize central sites for modifications underlying viewing-location-dependent and long-term adaptive changes in reflex performance.
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Jones, Gavin Eugene Guy. "The contributions of residual function and cross coupling to the horizontal angular vestibulo-ocular reflex after bilateral horizontal semicircular canal plugs." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape7/PQDD_0001/MQ45562.pdf.
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Han, Yanning Helen. "Investigations into Vestibular and Non-Vestibular Contributions to Eye Movements that Compensate for Head Rotations during Viewing of Near Targets." Case Western Reserve University School of Graduate Studies / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=case1105646958.
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Goode, Christopher T. "The development and recovery of vestibular reflexes in the domestic chicken /." Thesis, Connect to this title online; UW restricted, 1999. http://hdl.handle.net/1773/10632.
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Thurtell, Matthew James. "Effect of eye position on the three-dimensional kinematics of saccadic and vestibular-evoked eye movements." Thesis, The University of Sydney, 2005. http://hdl.handle.net/2123/1665.
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Saccadic and vestibular-evoked eye movements are similar in that their three-dimensional kinematic properties show eye position-dependence. When the line of sight is directed towards an eccentric target, the eye velocity axis tilts in a manner that depends on the instantaneous position of the eye in the head, with the magnitude of tilt also depending on whether the eye movement is saccadic or vestibular-evoked. The mechanism responsible for producing eye velocity axis tilting phenomena is not well understood. Some authorities have suggested that muscle pulleys in the orbit are critical for implementing eye velocity axis tilting, while others have suggested that the cerebellum plays an important role. In the current study, three-dimensional eye and head rotation data were acquired, using the magnetic search coil technique, to confirm the presence of eye position-dependent eye velocity axis tilting during saccadic eye movements. Both normal humans and humans with cerebellar atrophy were studied. While the humans with cerebellar atrophy were noted to have abnormalities in the two-dimensional metrics and consistency of their saccadic eye movements, the eye position-dependent eye velocity axis tilts were similar to those observed in the normal subjects. A mathematical model of the human saccadic and vestibular systems was utilized to investigate the means by which these eye position-dependent properties may arise for both types of eye movement. The predictions of the saccadic model were compared with the saccadic data obtained in the current study, while the predictions of the vestibular model were compared with vestibular-evoked eye movement data obtained in a previous study. The results from the model simulations suggest that the muscle pulleys are responsible for bringing about eye position-dependent eye velocity axis tilting for both saccadic and vestibular-evoked eye movements, and that these phenomena are not centrally programmed.
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Thurtell, Matthew James. "Effect of eye position on the three-dimensional kinematics of saccadic and vestibular-evoked eye movements." Faculty of Medicine, 2005. http://hdl.handle.net/2123/1665.
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Master of Science in MedicineSaccadic and vestibular-evoked eye movements are similar in that their three-dimensional kinematic properties show eye position-dependence. When the line of sight is directed towards an eccentric target, the eye velocity axis tilts in a manner that depends on the instantaneous position of the eye in the head, with the magnitude of tilt also depending on whether the eye movement is saccadic or vestibular-evoked. The mechanism responsible for producing eye velocity axis tilting phenomena is not well understood. Some authorities have suggested that muscle pulleys in the orbit are critical for implementing eye velocity axis tilting, while others have suggested that the cerebellum plays an important role. In the current study, three-dimensional eye and head rotation data were acquired, using the magnetic search coil technique, to confirm the presence of eye position-dependent eye velocity axis tilting during saccadic eye movements. Both normal humans and humans with cerebellar atrophy were studied. While the humans with cerebellar atrophy were noted to have abnormalities in the two-dimensional metrics and consistency of their saccadic eye movements, the eye position-dependent eye velocity axis tilts were similar to those observed in the normal subjects. A mathematical model of the human saccadic and vestibular systems was utilized to investigate the means by which these eye position-dependent properties may arise for both types of eye movement. The predictions of the saccadic model were compared with the saccadic data obtained in the current study, while the predictions of the vestibular model were compared with vestibular-evoked eye movement data obtained in a previous study. The results from the model simulations suggest that the muscle pulleys are responsible for bringing about eye position-dependent eye velocity axis tilting for both saccadic and vestibular-evoked eye movements, and that these phenomena are not centrally programmed.
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Chevallier, Aline. "Etude du rôle du récepteur aux hydrocarbures aromatiques ou AhR dans le développement et l’homéostasie du système nerveux de la souris C57BL/6J." Thesis, Paris 5, 2012. http://www.theses.fr/2012PA05P638/document.
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Le récepteur aux hydrocarbures aromatiques (AhR) est un facteur de transcription de la famille bHLH/PAS, activé par différents ligands exogènes dont les hydrocarbures aromatiques polycycliques ou halogénés (dioxines). A ce titre, il est décrit historiquement comme un récepteur de xénobiotiques dont le principal rôle est l’élimination de ces composés via la régulation des enzymes du métabolisme des xénobiotiques. Toutefois, des études récentes menées à l’aide de modèles souris invalidées pour le AhR, suggèrent indirectement que cette protéine régule des fonctions endogènes, notamment dans le système nerveux de mammifères dans lequel aucun rôle du AhR n’a jusqu’à présent été démontré. Nous avons donc utilisé le modèle de souris C57BL/6J AhR-/- pour mener à la fois des études comportementales et mécanistiques afin de déterminer ce rôle. Tout d’abord, nous avons identifié un défaut oculomoteur chez les souris AhR-/-, caractérisé par des mouvements spontanés horizontaux. En étudiant l’ensemble des circuits neurosensoriels potentiellement impliqués dans ce nystagmus pendulaire, nous avons montré que son origine est liée à des déficits du système visuo-moteur. De plus, en caractérisant et comparant les profils d’expression génique des cervelets de souris AhR+/+ et AhR-/- traitées ou non par de la 2,3,7,8 TétraChloroDibenzo-p-Dioxine (TCDD), nous avons montré que ce polluant, ligand du AhR, perturbait les fonctions endogènes du récepteur. Cet effet de « perturbation endogène » a été retrouvé dans un autre organe et est associé à une toxicité (fibrose hépatique). Cette étude a permis d’identifier de nouvelles fonctions physiologiques du AhR dans le système nerveux des souris, de caractériser un nouveau modèle animal de nystagmus pendulaire et ouvre de nouvelles perspectives de travail en neurotoxicologieThe AhR is a basic helix-loop-helix Per/ARNT/Sim family (bHLH-PAS) transcription factor which is activated by many diverse compounds including polyphenols and aromatic hydrocarbons such as 2,3,7,8 TétraChloroDibenzo-p-Dioxin (TCDD). Initially, the AhR was described as a ubiquitous xenobiotic-activated transcription factor which promotes the elimination of xenobiotics by regulating the expression of genes involved in xenobiotic metabolism. However, mouse AhR knockout models have demonstrated that the AhR also regulates other normal physiological functions. In particular, functioning of the nervous system of mammals, previously unexplored in this respect, might depend upon the activity of the AhR. We, thus, performed behavioral and gene expression studies in AhR-/- mice to discover these functions. We, first, found that AhR-/- mice exhibit an oculomotor deficit which is characterized by spontaneous horizontal pendular eye movements that are probably due to a deficit in the visuo-motor circuitry. Second, we found that the cerebellar gene expression profiles of AhR-/- as compared to AhR+/+ mice resembled those of AhR+/+ mice treated with TCDD (the ligand with the highest affinity for the AhR). This suggests that TCDD disrupts some normal physiological functions of the AhR in the nervous system. Third, AhR-/- mice and AhR+/+ treated with TCDD both develop liver fibrosis. This further suggests a role for the AhR in normal liver function. In conclusion, this study reveals new physiological functions for the AhR in the mouse nervous system and describes a new model of pendular nystagmus. Moreover, the results also provide novel research perspectives in the field of neurotoxicology
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OShea, Brittany L. "Eye Movement Control: An Index for Athleticism." VCU Scholars Compass, 2017. http://scholarscompass.vcu.edu/etd/5039.
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Athletic potential is one of the most complex human traits. An elite athlete is produced from a complex interaction of an innumerable number of traits exhibited by the athlete. However, it’s not clear whether these traits are innate, allowing the athlete to excel, or, alternatively, are a consequence of practice. To be successful, athletes rely heavily on sensory information from the visual and vestibular systems. This study investigated the relationship eye movement control has with innate athleticism by comparing the saccadic and Vestibulo-Ocular Reflex (VOR) responses of former, no longer practicing, elite athletes against their age and gender matched counterparts who were non-elite or non-athletes. Results showed subjects who participated in athletic activities longer (regardless of type or level achieved), showed both significantly better VOR suppression capabilities, as well as higher head velocities while suppressing their VOR. Although, these results are correlative in nature, they do not support the potential that VOR suppression is a learned trait of athletes. A longitudinal study would be required to assess this relationship fully.
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Kuldavletova, Olga. "L'intégration multisensorielle fonctionnelle et la plasticité des réflexes vestibulaires Vestibulo-sympathetic Reflex in Patients With Bilateral Vestibular Loss Influence of Graviceptor Stimulation Initiated by Off-Vertical Axis Rotation on Ventilation Effect of self-motion perception on autonomic control Vestibulo-Ocular Responses, Visual Field Dependence, and Motion Sickness in Aerobatic Pilots." Thesis, Normandie, 2020. http://www.theses.fr/2020NORMC405.
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L’objectif de ce travail de thèse était d’évaluer le rôle du système vestibulaire dans l’homéostasie en relation avec l’orientation.Nous avons évalué les réponses vestibulaires (1) dans une population normale pour évaluer le niveau d’implication des différents systèmes sensoriels dans la régulation cardiovasculaire et respiratoire et (2) dans des populations présentant des informations vestibulaires perturbées : soit des patients avec un déficit vestibulaire bilatéral soit des pilotes de voltiges aérienne.Les résultats indiquent que les informations vestibulaires et celles des gravicepteurs du tronc s’associent pour réguler la réponse respiratoire lors de la rotation à axe incliné selon la gravité (RAIG). La contribution respective des récepteurs vestibulaires et des gravicepteurs dans cette réponse varie en fonction des individus. Une autre étude a testé l’hypothèse selon laquelle la modulation de la réponse cardio-vasculaire par le système vestibulaire peut être influencée par les informations visuelles pendant la RAIG. Les résultats préliminaires de cette étude ont montré que la stimulation RAIG a un effet sur les valeurs moyennes des paramètres cardio-vasculaires. L'effet modulateur de la RAIG sur la pression artérielle a également été démontré. Cette modulation de réponse, et plus particulièrement la phase, variait entre les individus, ce qui peut indiquer la nature neuronale de la modulation observée. Un effet de la stimulation visuelle sur la modulation semble être également présent, mais une analyse plus approfondie est nécessaire pour confirmer ce résultat. Dans une autre étude, il s’est avéré que des patients présentant une déficience vestibulaire bilatérale avaient la même réponse cardio-vasculaire aux changements de position de la tête pendant le protocole « head down neck flexion » que les sujets témoins. Ces résultats indiquent que cette reconstruction du réflexe vestibulo-sympathique semble provenir de sources sensorielles autres que labyrinthiques. Enfin, nous avons étudié les pilotes de voltige aérienne comme modèle de sujets subissant des stimulations vestibulaires intenses et inhabituelles. Nous n'avons pas observé l’habituation vestibulaire attendue lors d’explorations fonctionnelles vestibulaires (RAIG et échelon de vitesse) en comparaison avec des sujets témoins, en revanche les pilotes étaient moins sensibles au mal des transports. Nous suggérons que les pilotes ne développent pas d'habituation vestibulaire comme attendu car ils ont besoin des réponses vestibulaires préservées et non altérées pour maintenir une performance optimum lors des activités de voltige aérienne.Nous concluons que pour générer des réponses en lien avec l’orientation, le système nerveux central intègre les signaux vestibulaires et non-vestibulaires et est sujet à un certain niveau de plasticité en conditions sensorielles altérées. Ce traitement multisensoriel est régulé individuellement, avec un poids variable des informations vestibulaires, en fonction de l'état sensoriel et des exigences liées à l’activitéThe aim of this thesis was to specify the role of the vestibular system in the orientation-related homeostasis. We evaluated vestibular responses to changes in orientation in space (1) in normal population to reveal in what proportion different sensory systems are implicated in the generation of the cardio-vascular and respiratory responses, and (2) in populations with altered vestibular afference: bilateral vestibular loss patients and aerobatic pilots.The results indicated that the vestibular system cooperates with trunk graviceptors to evoke respiratory response to changes in orientation during Off-Vertical Axis Rotation protocol (OVAR). The contribution of each sensory source was found to vary between individuals. Another study tested the hypothesis that the vestibular modulation of cardio-vascular parameters can be influenced by visual input during OVAR. Preliminary results from this study have demonstrated that the OVAR stimulation has an effect on the mean cardio-vascular parameters. The modulatory effect of OVAR on the arterial pressure has also been shown. The phases of modulation were varying between individuals which can indicate the neural nature of the observed modulation. The effect of visual stimulation on modulation has been detected, however further analysis is required. In another study, subjects presenting bilateral vestibular loss were shown to have the same cardio-vascular response to changes in the position of the head during Head-Down-Neck-Flexion protocol (HDNF) as normals. This reconstruction of the vestibulo-sympathetic reflex in human seems to originate from the sensory sources other than labyrinthine. Finally, we studied aerobatic pilots as humans experiencing intense and unusual vestibular stimulations. We have not revealed the expected vestibular habituation in the study using the OVAR and EVAR (Earth-Vertical Axis Rotation) stimulations, but were significantly less susceptible to motion sickness. We suggest that the pilots do not develop habituation, as they require unsuppressed responses for a better performance.We conclude that to generate the orientation-related responses, the Central Nervous System integrates the vestibular and non-vestibular signals and is subject to plastic changes in altered sensory conditions, if the response needs to be changed or restored. This multisensory processing is individually tuned, with the variable portion of vestibular impact in this processing, depending on activities, sensory state and the requirements to the response
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Black, Ross Arthur Graduate School of Biomedical Engineering Faculty of Engineering UNSW. "Compensatory strategies in humans performing active and passive gaze fixation and re-fixation tasks after unilateral vestibular deafferentation." Publisher:University of New South Wales. Graduate School of Biomedical Engineering, 2009. http://handle.unsw.edu.au/1959.4/43541.
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The human vestibulo-ocular reflex (VOR) stabilizes gaze during head movement. The reflex is typically tested in a clinic or laboratory using passive rotations or artificial stimuli which measure the amount of damage the vestibular apparatus has suffered. However, during everyday activities the vestibular system is stimulated by active, self generated head movements. Head movements are often rapid and associated with the goal of achieving either gaze-fixation or re-fixation. Patients who complain of on-going symptoms will typically identify a particular position or movement that aggravates their symptoms in their everyday life. There is a need to identify objective parameters which correlate with the subjective complaints of patients whose symptoms persist after vestibular damage. In the first study, a gaze-refixation task, patients who complain of ongoing symptoms (poorly-compensated), during rapid head turns, after unilateral vestibular de-afferentation (uVD) were compared with those who did not have the same complaints (well-compensated) and normal subjects. Well- and poorly-compensated groups were sorted according to responses on a standardized questionnaire. All subjects were then located in a real-world, non-laboratory environment in which poorly-compensated subjects reported experiencing symptoms. Each subjects head, eye and gaze displacement and velocity, head rotation frequency and blink or eye-lid closure were measured and analysed and compared between ipsi- and contra-lesional head rotations within and between subject groups. When subjects are able to generate their own active head rotations it has been suggested that a number of vestibular and extra-vestibular strategies might be employed to compensate for an impaired VOR. In subsequent studies, high resolution scleral search coils were used to identify the compensatory mechanisms used during active head rotations during a gaze-fixation task. A corrective saccade is typically observed during passive ipsilesional head rotations or impulses and might be potentiated during rapid, active or self-generated head rotations. The conditions which predict or contribute to the generation of the rapid, corrective eye movement were investigated. The results were compared with responses to passive head impulses of matched velocity and acceleration to determine if active head impulses could be used to identify a lesioned vestibular apparatus as is routinely clinically achieved with passive head impulses.
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Kuntzsch, Erik C. "Eye and Head Movements in Novice Baseball Players versus Intercollegiate Baseball Players." The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1492647251309525.
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Neimark, Matthew A. (Matthew Aaron). "Microgravity induced changes in horiztonal vestibulo-ocular reflexes of SLS-1 & SLS-2 astronauts." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/42791.
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Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1997.Includes bibliographical references (leaves 45-46).
by Matthew A. Neimark.
M.Eng.
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Manecy, Augustin. "Stratégies de guidage visuel bio-inspirées : application à la stabilisation visuelle d’un micro-drone et à la poursuite de cibles." Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAT050/document.
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Les insectes sont capables de prouesses remarquables lorsqu’il s’agit d’éviter des obstacles,voler en environnement perturbé ou poursuivre une cible. Cela laisse penser que leurs capacités de traitement, aussi minimalistes soient-elles, sont parfaitement optimisées pour le vol. A cela s’ajoute des mécanismes raffinés, comme la stabilisation de la vision par rapport au corps, permettant d’améliorer encore plus leurs capacités de vol.Ces travaux de thèse présentent l’élaboration d’un micro drone de type quadrirotor, qui ressemble fortement à un insecte sur le plan perceptif (vibration rétinienne) et reprend des points structurels clés, tels que le découplage mécanique entre le corps et le système visuel. La conception du quadrirotor (de type open-source), son pilotage automatique et son système occulo-moteur sont minutieusement détaillés.Des traitements adaptés permettent, malgré un très faible nombre de pixels (24 pixels seulement), de poursuivre finement du regard une cible en mouvement. A partir de là, nous avons élaboré des stratégies basées sur le pilotage par le regard, pour stabiliser le robot en vol stationnaire, à l’aplomb d’une cible et asservir sa position ; et ce, en se passant d’une partie des capteurs habituellement utilisés en aéronautique tels que les magnétomètres et les accéléromètres. Le quadrirotor décolle, se déplace et atterrit de façon autonome en utilisant seulement ses gyromètres, son système visuel original mimant l’oeil d’un insecte et une mesure de son altitude. Toutes les expérimentations ont été validées dans une arène de vol, équipée de caméras VICON.Enfin, nous décrivons une nouvelle toolbox qui permet d’exécuter en temps réel des modèles Matlab/Simulink sur des calculateurs Linux embarqués de façon complètement automatisée (http://www.gipsalab.fr/projet/RT-MaG/). Cette solution permet d’écrire les modèles, de les simuler, d’élaborer des lois de contrôle pour enfin, piloter en temps réel, le robot sous l’environnement Simulink. Cela réduit considérablement le "time-to-flight" et offre une grande flexibilité (possibilité de superviser l’ensemble des données de vol, de modifier en temps réel les paramètres des contrôleurs, etc.)Insects, like hoverflies are able of outstanding performances to avoid obstacles, reject disturbances and hover or track a target with great accuracy. These means that fast sensory motor reflexes are at work, even if they are minimalist, they are perfectly optimized for the flapping flight at insect scale. Additional refined mechanisms, like gaze stabilization relative to the body, allow to increase their flight capacity.In this PhD thesis, we present the design of a quadrotor, which is highly similar to an insect in terms of perception (visual system) and implements a bio-inspired gaze control system through the mechanical decoupling between the body and the visual system. The design of the quadrotor (open-source), itspilot and its decoupled eye are thoroughly detailed. New visual processing algorithms make it possible to faithfully track a moving target, in spite of a very limited number of pixels (only 24 pixels). Using this efficient gaze stabilization, we developed new strategies to stabilize the robot above a target and finely control its position relative to the target. These new strategies do not need classical aeronautic sensors like accelerometers and magnetometers. As a result, the quadrotor is able to take off, move and land automatically using only its embedded rate-gyros, its insect-like eye, and an altitude measurement. All these experiments were validated in a flying arena equipped with a VICON system. Finally, we describe a new toolbox, called RT-MaG toolbox, which generate automatically a real-time standalone application for Linux systems from a Matlab/Simulink model (http://www.gipsalab.fr/projet/RT-MaG/). These make it possible to simulate, design control laws and monitor the robot’s flight in real-time using only Matlab/Simulink. As a result, the "time-to-flight" is considerably reduced and the final application is highly reconfigurable (real-time monitoring, parameter tuning, etc.)
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Chiarovano, Elodie. "Instabilité posturale chez les séniors : dysfonction vestibulaire périphérique ou centrale ?" Thesis, Sorbonne Paris Cité, 2016. http://www.theses.fr/2016USPCB006.
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L’instabilité posturale est fréquente chez les séniors et peut entrainer la chute. La chute chez les séniors est un problème majeur de santé publique. Les chiffres épidémiologiques sont éloquents : une personne sur trois âgées de plus de 70 ans fera une chute dans l’année. Les causes sont multifactorielles : ostéo-articulaire, visuelle, cognitive, vestibulaire…. Dans cette étude, nous nous sommes intéressés à l’évolution de la fonction des récepteurs vestibulaires périphériques avec l’âge et à la perception de rotation à partir des entrées canalaires horizontales (système vestibulaire central et projections vestibulaires corticales). Notre but est d’essayer de comprendre l’implication du vieillissement du système vestibulaire dans l’instabilité posturale des séniors. Au niveau périphérique, nous avons quantifié la fonction des canaux semi-circulaires horizontaux par le test calorique et le vidéo-head impulse test. La fonction des récepteurs otolithiques (utriculaire et sacculaire) a été évaluée par les potentiels évoqués myogéniques recueillis au niveau cervical (voies sacculo-spinales) et oculaire (voies utriculo-oculaires). Au niveau central, la perception de l’entrée vestibulaire canalaire horizontale a été appréciée après irrigation à l’eau chaude du conduit auditif externe en appliquant un score de perception (présence ou absence de sensation rotatoire). Finalement, l’équilibre a été quantifié grâce au test d’organisation sensorielle sur l’Equitest et grâce à un système que nous avons récemment mis au point en collaboration avec le Professeur Curthoys à Sydney, comprenant une Wii Balance Board, un tapis mousse et un masque de réalité virtuelle (Oculus Rift). Les résultats ont montré une diminution des réponses oculaires au test calorique après 70 ans mais une absence de baisse du gain du réflexe vestibulo-oculaire horizontal au vidéo-head impulse test. La fonction otolithique, sacculaire et utriculaire, est altérée avec l’âge quelle que soit la stimulation utilisée (aérienne ou osseuse). La perception de l’entrée vestibulaire canalaire horizontale induite par une stimulation calorique nous a permis de montrer pour la première fois que certains séniors ne percevaient pas la sensation de rotation malgré une réponse oculaire normale (vitesse maximale de la phase lente du nystagmus oculaire supérieure à 15°/s). Dans notre population, nous avons pu ainsi définir deux types de séniors : un groupe présentant une perception de vertige rotatoire et un groupe « négligeant » ne pouvant pas reconstruire une sensation rotatoire à partir des entrées vestibulaires canalaires horizontales. La comparaison de ces deux groupes de séniors appariés sur l’âge ne montre aucune différence de la fonction canalaire horizontale ni de la fonction otolithique sacculaire et utriculaire. Néanmoins, les séniors négligents présentent en majorité des performances anormales (chute ou score diminué) à l’Equitest notamment en conditions 5 et 6. De plus, leur score au DHI est plus élevé relevant ainsi le handicape ressenti par ces séniors à cause de leur instabilité. En conclusion, les troubles de l’équilibre chez certains seniors pourraient résulter en partie d’une dysfonction vestibulaire centrale. Des études ultérieures permettront de déterminer si l’augmentation du seuil de perception rotatoire est un bon facteur prédictif du risque de chutePostural instability is common in seniors and can lead to falls which seniors are a major problem for Public Health. Epidemiological studies clearly show the magnitude of this problem: one in three people aged than more 70 years will fall in a year. This is caused by multiple factors including: musculoskeletal, visual, cognition, vestibular… The present study concerns the effect of age on the vestibular peripheral receptors function and on the perception of rotation from horizontal canal inputs (central vestibular processing and vestibular cortical projection). The aim is to try to understand the vestibular mechanisms involved in postural instability and mobility with age. At the peripheral level, the horizontal canal function was assessed using caloric test and video-Head Impulse Test. Otolith function (saccular and utricular) was assessed using vestibular evoked myogenic potentials recorded at cervical level (sacculo-spinal pathways) and at ocular level (utriculo-ocular pathways). At the central level, perception of motion from vestibular horizontal canal inputs was studied after caloric stimulation with warm water using a subjective perceptual score (presence or absence of rotatory vertigo). Finally, postural equilibrium was assessed with the Sensory Organization Test on the Equitest machine and also with a new system developed in collaboration with Prof. Curthoys (Sydney) using a Wii Balance Board, a foam rubber pad and a virtual reality headset (Oculus Rift DK2). Results showed decreased ocular responses induced by caloric stimulation after 70 years of age but healthy horizontal gain of the vestibulo-ocular reflex assessed by video-head impulse testing. The otolithic (saccular and utricular) function is impaired with age for all the stimuli used (air or bone conducted). Perception of motion induced by caloric stimulation (vestibular horizontal canal inputs) allowed us to show for the first time that some seniors are unable to feel the induced rotatory vertigo even with normal ocular responses (peak of the slow phase eye velocity higher than 15°/s). We defined two types of seniors: one senior group having a normal feeling of vertigo and one senior ‘neglect’ group who did not feel any sensation of rotation from horizontal canal inputs. The comparison of these two age-matched groups showed no difference in horizontal canal function, or otolithic function. The majority of the ‘neglect’ seniors with an absence of perception exhibited falls or a decreased score in conditions 5 and 6 during the Equitest. Moreover, their DHI scores were higher, showing the handicap induced by postural instability in these seniors. In conclusion, postural instability and falls in seniors may result from central vestibular impairment (inadequate central processing). A prospective study is needed to determine whether the increase perceptual threshold of rotation could be a good predictor of fall risk in seniors