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Timo P. Hirvonen - One of the best experts on this subject based on the ideXlab platform.

  • Motorized head impulse rotator for horizontal Vestibulo-Ocular Reflex: Normal responses.
    Archives of otolaryngology--head & neck surgery, 2007
    Co-Authors: Meeli Hirvonen, Heikki Aalto, Americo A. Migliaccio, Timo P. Hirvonen
    Abstract:

    Objective To characterize the horizontal angular Vestibulo-Ocular Reflex using a new motorized head impulse rotator and electro-oculography technique. Design Prospective case-control study. Participants We included 22 healthy volunteers with unpredictable, horizontal motorized head impulses with a mean velocity of 170°/s and a mean acceleration of 1550°/s2. We recorded head and eye position and calculated gain, asymmetry, and latency of the Vestibulo-Ocular Reflex. All subjects underwent testing twice while viewing a far (140 cm) target to evaluate the repeatability of the measurement. In addition, 8 of these subjects underwent testing while viewing a near (15 cm) target. We reported findings as mean ± SD. Results The mean gain during the 30-millisecond interval before peak head velocity and during the interval when head velocity ranged from 100°/s to 120°/s was 1.08 ± 0.10. The mean asymmetry in gain between sides was 3.7% ± 2.8%, and the mean latency of the Vestibulo-Ocular Reflex was 3.4 ± 6.3 milliseconds. There was a statistically significant correlation between consecutive gain measurements for each subject (r = 0.59;P=.004). The mean gain for the near target was 1.26 ± 0.10 and was significantly higher than that for the far target (P=.002). Conclusions The Vestibulo-Ocular Reflex measurements using our novel system are comparable to those achieved using other techniques. These results suggest that a motorized head impulse rotator with electro-oculography allows reliable and fast measurement of the Vestibulo-Ocular Reflex. In addition, the method is safe, repeatable, and thus could be a useful tool in the clinical assessment of the Vestibulo-Ocular Reflex.

  • A signal analysis technique of Vestibulo-Ocular Reflex stimulated with impulsive head movements.
    Annals of biomedical engineering, 2006
    Co-Authors: Martti Juhola, Heikki Aalto, Timo P. Hirvonen
    Abstract:

    Eye movements have been investigated in several areas of medicine and also elsewhere, such as in psychology or even in the development of human-computer interfaces. In the last few years we have designed a technique to stimulate, measure and analyze Vestibulo-Ocular Reflex eye movements. In the otoneurological literature these are seen as a novel and promising means of revealing certain disorders and diseases associated with vertigo. Vestibulo-Ocular Reflex is stimulated by impulsive head movements. We developed the present pattern recognition technique to detect the stimulus (impulsive head movements) and the Vestibulo-Ocular Reflex (response eye movements) generated from signals and to compute the latency and the gain values between them. Using our technique to calculate these attributes, we obtained clearly different results for a group of 22 dizzy patients than for a group of 30 healthy subjects.

  • MIE - On neural network classification of otoneurological cases on the basis of recognition results of Vestibulo-Ocular Reflex eye movements signal.
    Studies in health technology and informatics, 2006
    Co-Authors: Martti Juhola, Heikki Aalto, Timo P. Hirvonen
    Abstract:

    We constructed a signal analysis and recognition system to compute revealing results from Vestibulo-Ocular Reflex eye movements and their stimulation head movements of impulsive type that were generated as passive head movements with a special device designed by us for this purpose. Further, we implemented perceptron neural networks to separate healthy subjects from patients suffering from dysfunction of Vestibulo-Ocular Reflex in either ear. We gained high classification accuracies with this method ready for routine use.

  • Computational problems in the analysis of eye movement signals in the determination of Vestibulo-Ocular Reflex
    Computers and biomedical research an international journal, 1997
    Co-Authors: Juhola M, Heikki Aalto, Timo P. Hirvonen, Ilmari Pyykkö
    Abstract:

    The Vestibulo-Ocular Reflex preserves clear vision when the head is moving fast. Measurement of the Vestibulo-Ocular Reflex during the head autorotation test is usually calibrated using a dynamic technique in which the initial part of the eye movement signal and the corresponding part of the stimulating head movement signal are matched. Dynamic techniques can, however, be prone to generate excessively small or large calibration coefficients if a calibration segment of such a signal is corrupted by saccades or artifacts of large amplitudes. We have implemented an effective improvement for computation of difficult signals, not infrequent in clinical data, by limiting influence of distorting parts in the eye movement signal. We also discuss pitfalls of parameter accuracy concerning gain and phase parameters of the Vestibulo-Ocular Reflex that are used to differentiate abnormal results from the normal. Furthermore, we call the ubiquituous Fast Fourier Transform method into question with regard to these signals.

  • A comparison of static and dynamic calibration techniques for the Vestibulo-Ocular Reflex signal.
    International journal of clinical monitoring and computing, 1995
    Co-Authors: Timo P. Hirvonen, Heikki Aalto, Martti Juhola, Ilmari Pyykkö
    Abstract:

    We investigated two calibration techniques commonly used with eye movement signals pertaining to the Vestibulo-Ocular Reflex. Eye movement signals were recorded electro-oculographically as usual and calibrated using both static and dynamic calibration techniques. The calibration values of normals and patients were computed and compared to each other. Also gain parameters of Vestibulo-Ocular Reflex which depend on the calibration were computed. We found that both techniques are chiefly equally valid, and there are no considerable differences in results computed with either one.

Gabor Michael Halmagyi - One of the best experts on this subject based on the ideXlab platform.

  • Three-Dimensional Vibration-Induced Vestibulo-Ocular Reflex Identifies Vertical Semicircular Canal Dehiscence
    Journal of the Association for Research in Otolaryngology, 2011
    Co-Authors: Swee Tin Aw, Grace Elizabeth Aw, Michael John Todd, Andrew Philip Bradshaw, Gabor Michael Halmagyi
    Abstract:

    Vertical semicircular canal dehiscence (VSCD) due to superior canal dehiscence (SCD) or posterior canal dehiscence (PCD) of the temporal bone causes vestibular and cochlear hypersensitivity to sound. This study aimed to characterize the vibration-induced Vestibulo-Ocular Reflex (ViVOR) in VSCD. ViVORs in one PCD and 17 SCD patients, confirmed by CT imaging reformatted in semicircular canal planes, were measured with dual-search coils as binocular three-dimensional eye rotations induced by skull vibrations from a bone oscillator (B71—10 ohms) at 7 ms, 500 Hz, 135-dB peak-force level (re: 1 μN). The ViVOR eye rotation axes were computed by vector analysis and referenced to known semicircular canal planes. Onset latency of the ViVOR was 11 ms. ViVOR from VSCD was up to nine times greater than normal. The ViVOR’s torsional rotation was always contraversive-torsional (the eye’s upper pole rotated away from the stimulated ear), i.e. its direction was clockwise from a left and counterclockwise from a right VSCD, thereby lateralizing the side of the VSCD. The ViVORs vertical component distinguishes PCD from SCD, being downwards in PCD and upwards in SCD. In unilateral VSCD, the ViVOR eye rotation axis aligned closest to the dehiscent vertical semicircular canal axis from either ipsilateral or contralateral mastoid vibrations. However, in bilateral VSCDs, the ViVOR eye rotation axis lateralized to the ipsilateral dehiscent vertical semicircular canal axis. ViVOR was evoked in ossicular chain dysfunction, even when air-conducted click Vestibulo-Ocular Reflex (VOR) was absent or markedly reduced. Hence, ViVOR could be a useful measurement to identify unilateral or bilateral VSCD even in the presence of ossicular chain dysfunction.

  • Gentamicin vestibulotoxicity impairs human electrically evoked Vestibulo-Ocular Reflex
    Neurology, 2008
    Co-Authors: Michael J. Todd, Konrad P. Weber, Gabor Michael Halmagyi
    Abstract:

    Background: Electrical vestibular stimulation is believed to directly activate the vestibular afferents to mediate an electrically evoked Vestibulo-Ocular Reflex (eVOR). Gentamicin, an aminoglycoside antibiotic, induces vestibulotoxicity by hair cell damage and death. Objective: To determine if human eVOR is impaired by hair cell damage and death in systemic gentamicin vestibulotoxicity (GV). Methods: Three-dimensional binocular eye movements evoked by bilateral, bipolar, 100 msec direct current-step at intensities of 0.9, 2.5, 5.0, 7.5, and 10.0 mA were recorded with dual-search coils in 12 GV patients, and the results were compared to 13 healthy subjects. Results: Normal eVOR was predominantly torsional, comprising phasic eVOR initiation and cessation acceleration pulses at 9 msec latency after current onset and offset, with a tonic eVOR velocity-step during the 100 msec intervening period of maintained current. Normal phasic eVOR increased, while tonic eVOR scaled linearly, with current intensity. GV impaired phasic eVOR more severely than tonic eVOR, and prolonged the latency to 12–13 msec. In patients without mechanical response to vestibular tests, phasic eVOR was reduced to one-fifth of normal amplitude, doubled in duration, had reduced ability to vary with current intensity, and threshold was increased. Tonic eVOR was reduced to one-third of normal, but still scaled linearly with current intensity. Patients, who retained partial mechanical responses to vestibular tests, had phasic eVOR impairment without tonic eVOR abnormality. Conclusion: Impairment of evoked Vestibulo-Ocular Reflex (eVOR) in gentamicin vestibulotoxicity (GV) suggests that vestibular hair cells, activated by electrical stimulation, mediate the eVOR. Abnormalities of the eVOR, especially the phasic component, might be a marker of vestibular injury in GV. GLOSSARY: eVOR = electrically evoked Vestibulo-Ocular Reflex; EVS = electrical (galvanic) vestibular stimulation; GV = gentamicin vestibulotoxicity.

  • The click-evoked Vestibulo-Ocular Reflex in superior semicircular canal dehiscence.
    Neurology, 2003
    Co-Authors: Gabor Michael Halmagyi, Leigh A. Mcgarvie, R. A. Yavor, Michael John Todd
    Abstract:

    The authors studied eye movement responses to loud (110dB) clicks in 4 patients with Tullio effect due to superior semicircular canal dehiscence and in 9 normal subjects, by averaging the electro-oculogram. All 4 patients had small (0.1-0.3 deg) but easily reproducible vertical Vestibulo-Ocular Reflex eye movement responses to the clicks. Normal subjects had responses that were at least 10 times smaller. The click-evoked Vestibulo-Ocular Reflex test is a simple, robust way to screen dizzy patients for symptomatic superior semicircular dehiscence.

  • Effects of Unilateral Vestibular Deafferentation on the Linear Vestibulo-Ocular Reflex Evoked by Impulsive Eccentric Roll Rotation
    Journal of neurophysiology, 2003
    Co-Authors: Michael J. Todd, Leigh A. Mcgarvie, Americo A. Migliaccio, Gabor Michael Halmagyi
    Abstract:

    The effects of unilateral vestibular deafferentation (UVD) on the linear Vestibulo-Ocular Reflex (LVOR) were studied by measuring three-dimensional eye movements in seven UVD subjects evoked by imp...

Michael John Todd - One of the best experts on this subject based on the ideXlab platform.

  • Three-Dimensional Vibration-Induced Vestibulo-Ocular Reflex Identifies Vertical Semicircular Canal Dehiscence
    Journal of the Association for Research in Otolaryngology, 2011
    Co-Authors: Swee Tin Aw, Grace Elizabeth Aw, Michael John Todd, Andrew Philip Bradshaw, Gabor Michael Halmagyi
    Abstract:

    Vertical semicircular canal dehiscence (VSCD) due to superior canal dehiscence (SCD) or posterior canal dehiscence (PCD) of the temporal bone causes vestibular and cochlear hypersensitivity to sound. This study aimed to characterize the vibration-induced Vestibulo-Ocular Reflex (ViVOR) in VSCD. ViVORs in one PCD and 17 SCD patients, confirmed by CT imaging reformatted in semicircular canal planes, were measured with dual-search coils as binocular three-dimensional eye rotations induced by skull vibrations from a bone oscillator (B71—10 ohms) at 7 ms, 500 Hz, 135-dB peak-force level (re: 1 μN). The ViVOR eye rotation axes were computed by vector analysis and referenced to known semicircular canal planes. Onset latency of the ViVOR was 11 ms. ViVOR from VSCD was up to nine times greater than normal. The ViVOR’s torsional rotation was always contraversive-torsional (the eye’s upper pole rotated away from the stimulated ear), i.e. its direction was clockwise from a left and counterclockwise from a right VSCD, thereby lateralizing the side of the VSCD. The ViVORs vertical component distinguishes PCD from SCD, being downwards in PCD and upwards in SCD. In unilateral VSCD, the ViVOR eye rotation axis aligned closest to the dehiscent vertical semicircular canal axis from either ipsilateral or contralateral mastoid vibrations. However, in bilateral VSCDs, the ViVOR eye rotation axis lateralized to the ipsilateral dehiscent vertical semicircular canal axis. ViVOR was evoked in ossicular chain dysfunction, even when air-conducted click Vestibulo-Ocular Reflex (VOR) was absent or markedly reduced. Hence, ViVOR could be a useful measurement to identify unilateral or bilateral VSCD even in the presence of ossicular chain dysfunction.

  • The click-evoked Vestibulo-Ocular Reflex in superior semicircular canal dehiscence.
    Neurology, 2003
    Co-Authors: Gabor Michael Halmagyi, Leigh A. Mcgarvie, R. A. Yavor, Michael John Todd
    Abstract:

    The authors studied eye movement responses to loud (110dB) clicks in 4 patients with Tullio effect due to superior semicircular canal dehiscence and in 9 normal subjects, by averaging the electro-oculogram. All 4 patients had small (0.1-0.3 deg) but easily reproducible vertical Vestibulo-Ocular Reflex eye movement responses to the clicks. Normal subjects had responses that were at least 10 times smaller. The click-evoked Vestibulo-Ocular Reflex test is a simple, robust way to screen dizzy patients for symptomatic superior semicircular dehiscence.

Heikki Aalto - One of the best experts on this subject based on the ideXlab platform.

  • Using magnetic coil signals with EOG signals in computer analysis of Vestibulo-Ocular Reflex.
    Acta Oto-laryngologica, 2009
    Co-Authors: Martti Juhola, Heikki Aalto, Ilmari Pyykkö, Kirsi Setala
    Abstract:

    Since EOG signals are rather noisy, but magnetic coil signals almost noiseless, the latter type is a good reference to the former which is much easier to record. Concurrently recording magnetic coil and EOG signals we could verify some details as saccades which are often difficult to detect in noisy signals. It is important to recognise such phenomena in eye movement signals, because these affect the gain parameter computed between the Vestibulo-Ocular Reflex signal and the head movement signal.

  • Motorized head impulse rotator for horizontal Vestibulo-Ocular Reflex: Normal responses.
    Archives of otolaryngology--head & neck surgery, 2007
    Co-Authors: Meeli Hirvonen, Heikki Aalto, Americo A. Migliaccio, Timo P. Hirvonen
    Abstract:

    Objective To characterize the horizontal angular Vestibulo-Ocular Reflex using a new motorized head impulse rotator and electro-oculography technique. Design Prospective case-control study. Participants We included 22 healthy volunteers with unpredictable, horizontal motorized head impulses with a mean velocity of 170°/s and a mean acceleration of 1550°/s2. We recorded head and eye position and calculated gain, asymmetry, and latency of the Vestibulo-Ocular Reflex. All subjects underwent testing twice while viewing a far (140 cm) target to evaluate the repeatability of the measurement. In addition, 8 of these subjects underwent testing while viewing a near (15 cm) target. We reported findings as mean ± SD. Results The mean gain during the 30-millisecond interval before peak head velocity and during the interval when head velocity ranged from 100°/s to 120°/s was 1.08 ± 0.10. The mean asymmetry in gain between sides was 3.7% ± 2.8%, and the mean latency of the Vestibulo-Ocular Reflex was 3.4 ± 6.3 milliseconds. There was a statistically significant correlation between consecutive gain measurements for each subject (r = 0.59;P=.004). The mean gain for the near target was 1.26 ± 0.10 and was significantly higher than that for the far target (P=.002). Conclusions The Vestibulo-Ocular Reflex measurements using our novel system are comparable to those achieved using other techniques. These results suggest that a motorized head impulse rotator with electro-oculography allows reliable and fast measurement of the Vestibulo-Ocular Reflex. In addition, the method is safe, repeatable, and thus could be a useful tool in the clinical assessment of the Vestibulo-Ocular Reflex.

  • A signal analysis technique of Vestibulo-Ocular Reflex stimulated with impulsive head movements.
    Annals of biomedical engineering, 2006
    Co-Authors: Martti Juhola, Heikki Aalto, Timo P. Hirvonen
    Abstract:

    Eye movements have been investigated in several areas of medicine and also elsewhere, such as in psychology or even in the development of human-computer interfaces. In the last few years we have designed a technique to stimulate, measure and analyze Vestibulo-Ocular Reflex eye movements. In the otoneurological literature these are seen as a novel and promising means of revealing certain disorders and diseases associated with vertigo. Vestibulo-Ocular Reflex is stimulated by impulsive head movements. We developed the present pattern recognition technique to detect the stimulus (impulsive head movements) and the Vestibulo-Ocular Reflex (response eye movements) generated from signals and to compute the latency and the gain values between them. Using our technique to calculate these attributes, we obtained clearly different results for a group of 22 dizzy patients than for a group of 30 healthy subjects.

  • MIE - On neural network classification of otoneurological cases on the basis of recognition results of Vestibulo-Ocular Reflex eye movements signal.
    Studies in health technology and informatics, 2006
    Co-Authors: Martti Juhola, Heikki Aalto, Timo P. Hirvonen
    Abstract:

    We constructed a signal analysis and recognition system to compute revealing results from Vestibulo-Ocular Reflex eye movements and their stimulation head movements of impulsive type that were generated as passive head movements with a special device designed by us for this purpose. Further, we implemented perceptron neural networks to separate healthy subjects from patients suffering from dysfunction of Vestibulo-Ocular Reflex in either ear. We gained high classification accuracies with this method ready for routine use.

  • Computational problems in the analysis of eye movement signals in the determination of Vestibulo-Ocular Reflex
    Computers and biomedical research an international journal, 1997
    Co-Authors: Juhola M, Heikki Aalto, Timo P. Hirvonen, Ilmari Pyykkö
    Abstract:

    The Vestibulo-Ocular Reflex preserves clear vision when the head is moving fast. Measurement of the Vestibulo-Ocular Reflex during the head autorotation test is usually calibrated using a dynamic technique in which the initial part of the eye movement signal and the corresponding part of the stimulating head movement signal are matched. Dynamic techniques can, however, be prone to generate excessively small or large calibration coefficients if a calibration segment of such a signal is corrupted by saccades or artifacts of large amplitudes. We have implemented an effective improvement for computation of difficult signals, not infrequent in clinical data, by limiting influence of distorting parts in the eye movement signal. We also discuss pitfalls of parameter accuracy concerning gain and phase parameters of the Vestibulo-Ocular Reflex that are used to differentiate abnormal results from the normal. Furthermore, we call the ubiquituous Fast Fourier Transform method into question with regard to these signals.

Leigh A. Mcgarvie - One of the best experts on this subject based on the ideXlab platform.