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  • 1
    Electronic Resource
    Electronic Resource
    Effect of Head Orientation and Position on Vestibuloocular Reflex Adaptation (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 656 (1992), S. 0 
    Details
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1749-6632.1992.tb25206.x
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  • 2
    Electronic Resource
    Electronic Resource
    Velocity Storage in Labyrinthine Disorders (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 656 (1992), S. 0 
    Details
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1749-6632.1992.tb25216.x
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  • 3
    Electronic Resource
    Electronic Resource
    A HYPOTHETICAL EXPLANATION FOR PERIODIC ALTERNATING NYSTAGMUS: INSTABILITY IN THE OPTOKINETIC-VESTIBULAR SYSTEM (1981)
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 374 (1981), S. 0 
    Details
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1749-6632.1981.tb30906.x
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  • 4
    Electronic Resource
    Electronic Resource
    Motorische und sensorische Antworten bei Fusion vertikaler Disparitäten in verschiedenen Konvergenzstellungen (2000)
    Springer
    Der Ophthalmologe 97 (2000), S. 17-21 
    Details
    ISSN: 1433-0423
    Keywords: Schlüsselwörter Vertikale Fusionsbreite ; Konvergenz ; Key words Vertical fusion ; Convergence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: To study motor and sensory responses in vertical fusion at different angles of horizontal vergence in normal humans. Methods: The study included 12 normal subjects. A cross (+) extending 3.4°×3.2° was presented dichoptically. Vertical disparity was introduced by changing the vertical position of the cross in front of one eye. The disparity was incremented by 0.08° every 8 s. Distance viewing was tested with 1° of convergence demand, near vision with 6–15° convergence demand. Eye movements were recorded using three-axis search coils. Results: Vertical fusion capability was larger at near vision than at distance in 9 of 12 subjects. For the entire group, total vertical fusion capability (motor plus sensory response) differed between distance (mean 1.68°) and near (mean 2.39°). The motor component differed significantly between distance (mean 1.42°) and near (mean 2.13°). No difference in the sensory component was seen between distance (mean 0.26°) and near (mean 0.27°). Conclusions: Vertical fusion capability increases with convergence. This increase is mainly due to an increase of the motor response.
    Notes: Fragestellung: Untersucht wurde der Einfluß unterschiedlicher konvergenter Augenstellungen auf die vertikale Fusionsbreite. Methodik: 12 Normalpersonen wurde haploskopisch mit einer LCD-Brille ein Kreuz angeboten, das unter einem Gesichtswinkel von 3,4°×3,2° gesehen wurde. Vertikale Disparität wurde durch Verschiebung eines der beiden Kreuze um 0.08° alle 8 Sekunden nach oben oder nach unten erzeugt. Beim Fernblick betrug die Konvergenzanforderung 1°, beim Nahblick wurden je nach Proband zwischen 6 und 15° Konvergenzanforderung toleriert. Die jeweilige Augenlage wurde mit der Search-Coil-Methode registriert. Ergebnisse: Bei 9 der 12 Probanden war die vertikale Fusionsbreite bei Nahblick größer als bei Fernblick. Für die Gesamtgruppe zeigte die Gesamtfusion (Summe aus motorischer und sensorischer Fusion) einen signifikanten Unterschied zwischen Fernblick (MW 1,68°) und Nahblick (MW 2,39°). Die motorische Fusionsantwort war bei Nahblick signifikant größer (MW 2,13°) als bei Fernblick (MW 1,42°). Der sensorische Fusionsanteil zeigte keinen Unterschied (Nahblick MW 0,27°, Fernblick MW 0,26°). Schlussfolgerung: Die vertikale Fusionsbreite erhöht sich bei konvergenter Augenstellung durch eine Zunahme des motorischen Anteils an der Fusionsantwort.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003470050004
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  • 5
    Electronic Resource
    Electronic Resource
    Context-specific short-term adaptation of the phase of the vestibulo-ocular reflex (1998)
    Springer
    Experimental brain research 120 (1998), S. 184-192 
    Details
    ISSN: 1432-1106
    Keywords: Key words Vestibulo-ocular reflex ; Adaptation ; Neural integrator ; Motor learning ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  The phase of the angular vestibulo-ocular reflex (VOR) is subject to adaptive control. We had previously found that adapting the phase of the VOR also produced changes in drift on eccentric gaze-holding, implying a change in the time constant of the velocity-to-position neural integrator. Here we attempted to dissociate changes in gaze-holding drift from changes in the phase of the VOR. In normal human subjects, for 2 h, we alternated 5 min of VOR phase adaptation (sinusoids, 0.2 Hz) with 5 min of making saccades in the light with the head stationary. Afterwards, changes in VOR phase were the same (32% of requested) as those obtained with 1 h of phase adaptation alone, but changes in drift following saccades were much smaller than those found after phase adaptation alone (0.8°/s compared with 5°/s). When measuring drift after VOR steps, however, the changes were closer to those found after phase adaptation alone (3.8°/s). To test the relationship between gaze-holding drift after VOR steps and adaptive changes in VOR phase, we alternated sinusoidal VOR phase adaptation with normal VOR steps in the light. In this paradigm, the adaptive change in VOR phase was about the same as with phase-adaptation alone (35%), but there was now little drift after saccades (1.9°/s) or after VOR steps (0.7°/s). We conclude that the state of the velocity-to-position neural integrator can be altered selectively and rapidly depending upon the task required. Such context-specific adaptation is advantageous, because it allows adjustment of the phase of the VOR without degrading the ability to hold eccentric fixation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002210050392
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  • 6
    Electronic Resource
    Electronic Resource
    Short-term adaptation of the phase of the vestibulo-ocular reflex (VOR) in normal human subjects (1995)
    Springer
    Experimental brain research 106 (1995), S. 318-326 
    Details
    ISSN: 1432-1106
    Keywords: Vestibulo-ocular reflex ; Adaptation ; Neural integrator ; Motor learning ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We investigated the effects of short-term vestibulo-ocular reflex (VOR) adaptation on the gain and phase of the VOR, and on eccentric gaze-holding in darkness, in five normal human subjects. For 1 h, subjects sat in a chair that rotated sinusoidally at 0.2 Hz while surrounded by a visual stimulus (optokinetic drum). The drum was rotated relative to the chair, to require a VOR with either a phase lead or lag of 45 deg (with respect to a compensatory phase of zero) with no change in gain, or a gain of 1.7 or 0.5 with no change in phase. Immediately before and after each training session, VOR gain and phase were measured in the dark with 0.2 Hz sinusoidal rotation. Gaze-holding was evaluated following 20 deg eccentric saccades in darkness. Adaptation paradigms that called only for a phase lead produced an adapted VOR with 33% of the required amount of phase change, a 20% decrease in VOR gain, and an increased centripetal drift after eccentric saccades made in darkness. Adaptation paradigms that called for a phase lag produced an adapted VOR with 29% of the required amount of phase change, no significant change in VOR gain, and a centrifugal drift after eccentric saccades. Adaptation paradigms requiring a gain of 1.7 produced a 15% increase in VOR gain with small increases in phase and in centripetal drift. Adaptation paradigms requiring a gain of 0.5 produced a 31% decrease in VOR gain with a 6 deg phase lag and a centrifugal drift. The changes in drift and phase were well correlated across all adaptation paradigms; the changes in phase and gain were not. We attribute the effects on phase and gaze-holding to changes in the time constant of the velocity-to-position ocular motor neural integrator. Phase leads and the corresponding centripetal drift are due to a leaky integrator, and phase lags and the corresponding centrifugal drift are due to an unstable integrator. These results imply that in the short-term adaptation paradigm used here, the control of drift and VOR phase are tightly coupled through the neural integrator, whereas VOR gain is controlled by another mechanism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00241127
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  • 7
    Electronic Resource
    Electronic Resource
    Short-term vestibulo-ocular reflex adaptation in humans (1994)
    Springer
    Experimental brain research 100 (1994), S. 316-327 
    Details
    ISSN: 1432-1106
    Keywords: Vestibulo-ocular reflex ; Adaptation Neural integrator ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We investigated the effect of short-term vestibulo-ocular reflex (VOR) adaptation in normal human subjects on the dynamic properties of the velocity-to-position ocular motor integrator that holds positions of gaze. Subjects sat in a sinusoidally rotating chair surrounded by an optokinetic nystagmus drum. The movement of the visual surround (drum) was manipulated relative to the chair to produce an increase (× 1.7 viewing), decrease (× 0.5, × 0 viewing), or reversal (× (-2.5) viewing) of VOR gain. Before and after 1 h of training, VOR gain and gaze-holding after eccentric saccades in darkness were measured. Depending on the training paradigm, eccentric saccades could be followed by centrifugal drift (after × 0.5 viewing), implying an unstable integrator, or by centripetal drift [after × 1.7 or × (-2.5) viewing], implying a leaky integrator. The changes in the neural integrator appear to be context specific, so that when the VOR was tested in non-training head orientations, both the adaptive change in VOR gain and the changes in the neural integrator were much smaller. The changes in VOR gain were on the order of 10% and the induced drift velocities were several degrees per secend at 20 deg eccentric positions in the orbit. We propose that (1) the changes in the dynamic properties of the neural integrator reflect an attempt to modify the phase (timing) relationships of the VOR and (2) the relative directions of retinal slip and eye velocity during head rotation determine whether the integrator becomes unstable (and introduces more phase lag) or leaky (and introduces less phase lag).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00227201
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  • 8
    Electronic Resource
    Electronic Resource
    Short-term vestibulo-ocular reflex adaptation in humans (1994)
    Springer
    Experimental brain research 100 (1994), S. 328-336 
    Details
    ISSN: 1432-1106
    Keywords: VOR ; Adaptation ; Visual-vestibular conflict ; Retinal slip ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We oscillated humans sinusoidally at 0.2 Hz for 1 h, using various combinations of rotations of the head and visual surround to elicit short-term adaptation of the gain of the vestibulo-ocular reflex (VOR). Before and after each period of training, the gain of the VOR was measured in darkness, in response to a position step of head rotation. A small foveal target served as well as a full-field stimulus at driving VOR adaptation. Oscillation of the visual surround alone produced a substantial increase in the VOR gain. When the visual scene was rotated in phase with the head but with a larger amplitude to produce a reversal of the VOR, the VOR gain increased if the movement of the visual scene was much greater than that of the head, otherwise the gain decreased. We interpreted these results with a model of VOR adaptation that uses as its “error signal” the combination of motion of images on the retina (retinal slip) and any additional slow-phase eye velocity, beyond that generated by the VOR through the vestibular nuclei, necessary to prevent such retinal slip during head rotation. The slow phase velocity generated by the VOR is derived from “inferred head rotation”, a signal based on the discharge of neurons in the vestibular nuclei that receive both labyrinthine and visual (optokinetic) inputs. The amplitude and sign of the ratio of the “error signal” to “inferred head velocity” determine the amplitude and the direction (increase or decrease) of VOR gain adaptation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00227202
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  • 9
    Electronic Resource
    Electronic Resource
    A hypothetical explanation of congenital nystagmus (1984)
    Springer
    Biological cybernetics 50 (1984), S. 119-134 
    Details
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract Congenital nystagmus (CN) is a conjugate, rhythmic, eye movement disorder characterized by a wide variety of waveforms ranging from jerk to pendular types. No detailed mechanisms have been proposed to explain the generation of the CN wave-form This paper proposes a hypothetical mechanism for CN, and shows with computer simulations that a model based on this hypothesis can account for a variety of disparate waveforms. The basis of this model is a gaze-holding network, or neural integrator, that has both position and velocity feedback loops. The signals carried in these loops could arise from either afference or efference. In normal subjects, the position feedback would be positive and the velocity feedback would be negative. Both would help to increase the time constant of an imperfect neural integrator in the brain stem. We propose that in patients with CN the sign of the velocity pathway is reversed, making the neural integrator unstable. This instability could manifest as many different CN waveforms, depending on the direction and velocity of post-saccadic ocular drift and actions of nonlinearities within the position and velocity feedback loops. Thus a single underlying abnormality may be responsible for a variety of CN waveforms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00337159
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  • 10
    Electronic Resource
    Electronic Resource
    Polymorphism of malate dehydrogenase in Ascaris suum (1970)
    Springer
    Biochemical genetics 4 (1970), S. 253-257 
    Details
    ISSN: 1573-4927
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Starch gel electrophoresis of homogenates prepared from adult Ascaris suum revealed polymorphism for the number, staining intensity, and electrophoretic mobility of the cytoplasmic isozymes of malate dehydrogenase (MDH). Five different variant isozymic patterns were found among the 2160 worms surveyed. The most acceptable formulation for the molecular basis of the variant patterns supports the hypothesis that the synthesis of supernatant MDH in Ascaris suum is under the control of two separate genetic loci, MDH A and MDH B.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00485776
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