The Use of Virtual Reality for Persons with Balance Disorders

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The Use of Virtual Reality for Persons with
Balance Disorders

• Susan L. Whitney, PT, PhD, NCS, ATC
• University of Pittsburgh
• Supported by the National Institute on Deafness
  and Other Communication Disorders

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Introduction

• The use of virtual reality with persons with
  vestibular disorders is a relatively new concept
• Persons with vestibular disorders often complain
  of having difficulty maintaining their balance
  when exposed to complex visual scenes

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Introduction

• Persons with vestibular disorders have abnormally
  large, visually induced postural responses
• It is impossible to replicate visually complex
  visual environments in a rehabilitation setting
  and control the input

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The BNAVE (Balance Cave Automatic Virtual
Environment)

• It was custom built with a viewing angle of 200
  degrees horizontal and 90 degrees vertical
  (Figure 3)
• Each display (3) is produced by a VREX 2210
  LCD-based stereoscopic digital projector
  controlled by an Intel PIII computer

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The BNAVE (Balance Cave Automatic Virtual
Environment)

• Lab View software is used to interface the
  signals between the software and hardware
• Data from the force platform and head sensor were
  sampled at 120 Hz

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Design of the BNAVE
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Postural Sway in a Virtual Environment in
Patients With Unilateral Peripheral Vestibular
Lesions

• Susan L. Whitney, PhD, PT, NCS, ATC
• Patrick J. Sparto, PhD, PT
• Kathryn E. Brown, MS, PT, NCS
• Mark S. Redfern, PhD
• Joseph M. Furman, MD, PhD
• Departments of Physical Therapy, Otolaryngology
  and Bioengineering
• University of Pittsburgh

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Introduction

• Vestibular compensation adjusts for abnormalities
  in the vestibulo-ocular reflex (VOR) and postural
  stability seen acutely following unilateral
  peripheral vestibular lesions (UPVL).
• Long term visual dependence of individuals with
  UPVL has not been fully examined.
• Also, the ability to receive cues from the
  periphery in these individuals has not been
  studied.

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Purpose

• The goal of this study was to assess the visual
  motion sensitivity of patients with chronic
  UPVLs.
• Another objective was to determine the amount of
  discomfort each individual perceived after each
  trial.

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Methods

• 24 gender and age matched patients and controls
  were recruited to participate.
• Gender males 10 females 14.
• Age Range 31 66 Mean 49.5 10.
• Patients time (in months) since unilateral
  peripheral vestibular loss
• Range 10 72 mos.
• Mean 38.9 21.5 mos.

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Methods

• Each subject participated in one 8-trial virtual
  reality session.
• There was an initial and final quiet trial with
  nothing displayed on the screen.

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Methods

• Each subject was tested under 3 different field
  of view conditions (FOV).
• Full vision.
• Peripheral vision only (30º).
• Central vision only (30º).

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Methods

• Each subject was also tested under 2 different
  frequencies of visual scene movement in a
  sinusoidal fashion.
• 0.1 Hz movement.
• 0.25 Hz movement.

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Experimental Design

• Independent variables
• FOV
• Frequency of tunnel movement
• SUDS rating
• Dependent variable
• Amount of sway

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Methods

• Subjects stood on force platform with their feet
  comfortably apart, wearing a harness support to
  prevent a potential fall, measuring center of
  pressure (COP).
• The subjects head movement was measured using an
  electromagnetic position and orientation sensor
  affixed to an adjustable plastic headband.

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Methods

• Eye movement was monitored to insure that eyes
  remained straight ahead.
• All data was collected with the room darkened.

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Methods

• Preliminary objective and subjective data
  collected include ABC, DHI, BP, HR, Situational
  Characteristics Questionnaire, and the Simulator
  Sickness Questionnaire.
• BP, HR, and level of discomfort (Subjective Units
  of Discomfort SUDs) measured prior to start of
  trial.

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Methods

• SUDs were measured after each trial.
• BP and HR were measured in the middle of the
  session and again at the end.
• When measuring level of discomfort or anxiety,
  the subject is asked to rate their level on a
  scale of 0 to 100 with 100 being the greatest.

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Methods

• A visual stimulus of an infinitely long tunnel
  with checkered walls was displayed in the BNAVE,
  a virtual environment display facility.
• Subjects stood barefoot for 80 seconds while
  viewing sinusoidal movements of the virtual
  tunnel.
• Sixty seconds of movement were preceded and
  followed by 10 seconds of quiet standing.

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Data Analysis

• Analysis of variance with repeated measures was
  used to test for the effects of subject group,
  movement frequency and FOV condition.
• Non-parametric statistics were used to look at
  the main effects of the independent variables on
  the SUDs.
• Non-parametric correlation coefficient was used
  to examine the association between sway and the
  SUDs.

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Results FOV Frequency

• There was no difference in amount of sway
  elicited in patients vs. control group,
  regardless of FOV condition or frequency of
  visual scene movement.
• The amount of sway was significantly affected by
  FOV (p.000).
• The amount of sway was significantly affected by
  frequency of visual scene movement (p.003).

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Results FOV Conditions
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Results Frequency vs. Sway
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Results

• The SUDs level was significantly affected by FOV
  (p.000).
• The correlation between the SUDs and sway was
  significant (rs .32, p.000 n137).
• Many of the SUDs scores were clustered between 0
  and 10.

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Sway vs. SUDs levels
SUDs gt 10
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Conclusion

• FOV significantly influences visual
  motion-induced sway in normal and in patients
  with chronic UPVL.
• Frequency of visual scene movement also
  significantly influences sway in normal and in
  patients with chronic UPVL.
• Level of discomfort (SUDs) is significantly
  affected by FOV in normal and patients with
  chronic UPVL.