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
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
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
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
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
Design of the BNAVE
Right side
projector.
Left side
projector.
Front
projector.
Sinusoid, 0.1 Hz
Sinusoid 0.1 Hz, 4 sq./m, 4 m/s
5
0.35
4
3
RMS A-P COP (cm)
COP, Hea d X-lation (c m)
0.3
2
1
0
-1
-2
0.2
2 m/s
4 m/s
0.15
0.1
-3
Head
-4
COP
-5
0.25
0
10
20
30
Time(sec)
40
50
0.05
60
0
2 SQ/m
4 SQ/m
Block Size
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
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.
Purpose
• The goal of this study was to assess the
visual motion sensitivity of patients with
chronic UPVL’s.
• Another objective was to determine the
amount of discomfort each individual
perceived after each trial.
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.
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.
Methods
• Each subject was tested under 3 different
field of view conditions (FOV).
– Full vision.
– Peripheral vision only (30º).
– Central vision only (30º).
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.
Experimental Design
• Independent variables:
– FOV
– Frequency of tunnel movement
– SUDS rating
• Dependent variable
– Amount of sway
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.
Methods
• Eye movement was monitored to insure that
eyes remained straight ahead.
• All data was collected with the room
darkened.
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.
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.
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.
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.
Pt 2, 0.10 Hz, Peripheral Vision
6
Head Position (cm)
Tunnel Position (m)
4
2
0
-2
-4
Head Position
Tunnel Position
-6
0
10
20
30
40
Time (s)
50
60
70
80
Pt 2, 0.10 Hz, Central Vision
6
Head Position (cm)
Tunnel Position (m)
4
2
0
-2
-4
Head Position
Tunnel Position
-6
0
10
20
30
40
Time (s)
50
60
70
80
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).
Results – FOV Conditions
Effect of FOV on Sway
0.7
RMS in cm
0.6
0.5
0.4
0.3
0.2
0.1
0
Full
Peripheral
Central
Results – Frequency vs. Sway
Effect of Frequency of Movement on Sway
0.6
0.5
0.4
0.3
0.2
0.1
0
0.1 Hz
0.25 Hz
Results
• The SUDs level was significantly affected
by FOV (p=.000).
• The correlation between the SUDs and sway
was significant (rs= .32, p=.000; n=137).
– Many of the SUDs scores were clustered
between 0 and 10.
Effect of FOV on Perceived Level of
Discomfort/Anxiety
20
15
10
5
0
Full
Peripheral
Central
SWAY
Sway vs. SUDs levels
4
3
2
1
1='pt',2=cn'
2.00
0
1.00
-20
SUDS
0
20
SUDs > 10
40
60
80
100
Conclusion
• FOV significantly influences visual motioninduced 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.