The Study of Visually-Induced Postural Responses Using Virtual Environments

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

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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

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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

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BNAVE Layout
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Sensory Integration

• Modified Neurotest posture platform
• Pitch and A-P translation
• Treadmill
• Galvanic Vestibular Stimulation

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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

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Stimulus

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

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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

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Adults CON v. UVL
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Phase-locked
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Not Phase-locked
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Phase-locking behavior
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90
Phase v. Frequency
3
60
120
2
30
150
1
180
0
210
330
UVL 0.1
CON 0.1
UVL 0.25
240
300
CON 0.25
270
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90
CON v. UVL 0.1 Hz
3
60
120
2
30
150
1
180
0
210
330
UVL 0.1
CON 0.1
240
300
270
20
90
CON v. UVL 0.25 Hz
3
60
120
2
30
150
1
180
0
210
330
UVL 0.25
240
300
CON 0.25
270
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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

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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

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Healthy Adults v. Children
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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

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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

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Current Areas of Research

• Visual Influences in Height Phobia
• Visual Influences in Migraine
• Vestibular Rehabilitation using VR

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