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The Study of Visually-Induced Postural Responses Using Virtual Environments

The Study of Visually-Induced Postural Responses Using Virtual Environments Sparto PJ, Furman JM, Jacobson JL, Whitney SL, Hodges LF, Redfern MS Department of Otolaryngology University of Pittsburgh, PA, USA. Sponsors: Eye and Ear Foundation, NIH: DC02490, DC05205, K25 AG001049.

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The Study of Visually-Induced Postural Responses Using Virtual Environments

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  1. The Study of Visually-Induced Postural Responses Using Virtual Environments Sparto PJ, Furman JM, Jacobson JL, Whitney SL, Hodges LF, Redfern MS Department of Otolaryngology University of Pittsburgh, PA, USA Sponsors: Eye and Ear Foundation, NIH: DC02490, DC05205, K25 AG001049

  2. Collaborators Rolf Jacob, MD Kathryn Brown, MS, PT Jeffrey Jasko, BS Leigh Mahoney, MS Chad Wingrave, MS

  3. Visually-Induced Postural Sway Research • Vestibular disorders (Redfern and Furman, 1994) • Anxiety disorders (Jacob et al., 1995) • Healthy elders (Borger et al., 1999) • Adaptation (Loughlin et al., 1996, Loughlin and Redfern, 2001)

  4. Limitations • Single rear-projected screen • Restricted in field of view (60 deg) • Not able to study peripheral motion cues • Modified Equitest platform • Pitch motion only • Frequency and amplitude range limited

  5. Balance NAVE Automatic Virtual Environment (BNAVE) • Spatially-Immersive VR Facility used to generate moving visual environments • Can control many factors: • Field of view (180o H x 110o V) • Spatial and temporal characteristics of movement • Spatial frequency • Monoscopic & stereoscopic

  6. BNAVE Layout

  7. Sensory Integration • Modified Neurotest posture platform • Pitch and A-P translation • Treadmill • Galvanic Vestibular Stimulation

  8. Subjects • Healthy Adults (CON) • 5 Males, 6 Females • Age 32 - 66 years, mean 49 + 11 yrs • No abnormalities on clinical vestibular tests • Adults with Unilateral Vestibular Loss (UVL) • 5 Males, 6 Females • Age 32 - 66 years, mean 49 + 11 yrs • 10 - 72 months post vestibular n. section

  9. Stimulus • Frequency of Movement • 0.1 Hz • 0.25 Hz • RMS velocity was 1.2 m/s for both freq.

  10. Data Analysis • A-P Head Position sampled at 20 Hz using electromagnetic tracker • RMS amplitude of sway computed at stimulus frequency • Linear, Time-Invariant and Dynamic Systems Analyses

  11. Adults – CON v. UVL

  12. 70 50 Head PSD 30 10 0 0.1 0.3 0.5 0.7 0.9 Frequency (Hz) 6 4 2 Head Sway (cm) 0 -2 -4 10 20 30 40 50 60 70 80 Time (sec) Phase-locked

  13. 4 3 Head PSD 2 1 0 0.1 0.3 0.5 0.7 0.9 Frequency (Hz) 6 4 2 Head Sway (cm) 0 -2 -4 10 20 30 40 50 60 70 80 Time (sec) Not Phase-locked

  14. Controls (n=11) Subjects with Unilateral Vestibular Loss (n=11) 0.1 Hz 0.25 Hz 0.1 Hz 0.25 Hz Primary peak in PSD at stimulus frequency 7 4 6 4 Phase-lock during 1st cycle 4 4 4 4 Phase-lock for all subsequent cycles 5 3 4 3 Phase-locking behavior

  15. 90 Phase v. Frequency 3 120 60 2 150 30 1 180 0 210 330 UVL – 0.1 CON – 0.1 UVL – 0.25 240 300 CON – 0.25 270

  16. 90 CON v. UVL 0.1 Hz 3 120 60 2 150 30 1 180 0 210 330 UVL – 0.1 CON – 0.1 240 300 270

  17. 90 CON v. UVL 0.25 Hz 3 120 60 2 150 30 1 180 0 210 330 UVL – 0.25 240 300 CON – 0.25 270

  18. Conclusions • Peripheral stimulus induces sway in ½ subjects at 0.1 Hz, and 1/3 subjects at 0.25 Hz • Subjects with compensated UVL sway the same amount as controls • Subjects with UVL have different timing at 0.25 Hz

  19. Adults v. Children (8-12 y.o.) • Healthy Adults (CON) • 5 Males, 6 Females • Age 32 - 66 years, mean 49 + 11 yrs • No abnormalities on clinical vestibular tests • Children • 5 Males, 5 Females • Age 8 - 12 years, mean 10 + 1 yrs • No abnormalities on clinical vestibular tests

  20. Healthy Adults v. Children

  21. Conclusions • Greater sway at higher frequencies • Children aged 8-12 years still do not show adult pattern of visually-induced sway • Vestibular and somatosensory threshold for postural control may be higher

  22. Conclusions • Visually-induced postural sway is a complex problem, dependent on many factors • visual field of view • optic flow structure • spatial and temporal frequency of stimulus • Relevant to many clinical problems

  23. Current Areas of Research • Visual Influences in Height Phobia • Visual Influences in Migraine • Vestibular Rehabilitation using VR

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