Symptom Expression during Virtual Reality Exposure

1
Symptom Expression during Virtual Reality
Exposure Susan L. Whitney1,2, Patrick J.
Sparto1,2,3, Larry Hodges4, Joseph M. Furman1,2,
and Mark S. Redfern1,2,3 Departments of
1Otolaryngology, 2Physical Therapy, and
3Bioengineering, University of Pittsburgh,
Pittsburgh, PA and the 4University of North
Carolina at Charlotte
Abstract Background The long term aim of this
study was to determine if full field virtual
reality (VR) exposure results in different
symptom profiles in persons with vestibular
disorders and controls. Methods Subjects
consisted of 6 symptomatic persons with
peripheral vestibular hypofunction (PVH mean age
57, range 35-77 years) and 21 healthy controls
(mean age 48, range 22-83 years). Subjects
performed 8 different head and eye coordination
tasks. All eight tasks were performed on 6
different days, with each day consisting of
exposure to either a stationary scene (2 days) or
optic flow (4 days). The scenes were generated
using a back-projected immersive VR system that
provided full-field antero-posterior motion. All
subjects were asked to express their subjective
units of discomfort (SUDS, 0 to 10 scale) and to
complete the Simulator Sickness Questionnaire
(SSQ, 16 items, 0 to 3 scale) after each
90-second trial. Responses were dichotomized into
either a no (score of 0) or yes (score
greater than 0, i.e. they experienced some
symptom) immediately following each trial for the
SUDS, total SSQ, and each of the 3 SSQ subscales
(nausea, disorientation, and oculomotor).
Results There was a significant association
between subject group and the proportion of yes
responses (chi-square, plt0.001) for all measures.
The percentage of trials in which some symptoms
occurred in the control and vestibular groups
(CONPVH) were as follows SUDS (1955) SSQ
total (2557) SSQ nausea (1240) SSQ
disorientation (550) and the SSQ oculomotor
(2451). Conclusion Patients with vestibular
disorders appear to experience more discomfort
than controls during virtual reality immersion.

• Number of symptoms reported on SSQ
• For the SSQ, the proportion of trials rated as
  moderate (2) or severe (3) was small
• Controls 0.5 of the trials
• Patients 2.9 of the trials
• Thus, as a measure of how well subjects
  tolerated the tasks, for each trial we quantified
  how many symptoms were rated gt 0, within each
  subscale and in total.
• The tasks elicited a a greater number of
  symptoms in subjects with PVH compared with
  controls (p lt 0.001) (Figure 3B).
• For control subjects, the number of symptoms was
  not associated with session number, trial number,
  optic flow condition (I.e. contrast and spatial
  frequency), or gaze task.

Figure 1. Examples of the VR scenes with high
(left) and low (right) spatial frequency.

• Results
• Frequency of symptoms
• In the control group, subjects reported no
  symptoms for SUDs or SSQ in at least 75 of the
  trials. Therefore, for each trial a binary score
  of 0 or 1 was assigned to the SUDs or SSQ
  subscales, based on
• SUDs
• 0 assigned if subject reported SUDs 0
• 1 assigned if subject reported SUDs gt 0
• SSQTotal and subscales
• 0 assigned if subject reported 0 for all items
  in subscale or total
• 1 assigned if subject reported gt0 for any item
  in subscale or total
• The frequency of non-zero SUDs and SSQ scores
  was greater after the performance of gaze tasks
  compared with the initial rating.
• The frequency of non-zero SUDs and SSQ scores
  was 2 to 10 times greater in the subjects with
  PVH compared with controls (Figure 2). The
  frequency of non-zero responses was significantly
  associated with subject group, using ?2 test (p lt
  0.0001).
• The frequency of symptoms was not associated
  with session number, trial number, optic flow
  condition (I.e. contrast and spatial frequency),
  or gaze task.

Introduction Patients with vestibular disorders
often complain of having difficulty with their
balance and have increased symptoms in situations
where there are complex visual scenes and
changing visual stimuli (e.g., supermarkets,
shopping malls). Virtual Reality (VR) has been
proposed as a potentially useful technique in the
rehabilitation of patients with balance disorders
by exposing patients to various environments. VR
can allow the physical therapist a degree of
control over the environment that is not normally
possible (Ring, 1998). However, the ability of
persons with vestibular disorders to tolerate VR
exposure is not well understood. This pilot
study examined the amount of discomfort and
simulator sickness symptoms experienced by
persons with and without vestibular disorders to
various VR environments.

• Subjects performed 8 different head and eye
  coordination tasks while standing in the BNAVE on
  each of 6 visits (Table 2). Each task was
  performed for 90 s.

• Summary of Results
• Patients reported more symptoms than controls
  during gaze tasks within an immersive visual
  environment however, severe symptoms were rare
  in both groups.
• The type of optic flow condition (spatial
  frequency and contrast) did not have an effect of
  the responses of either patients or controls.
• Conclusion
•  In conclusion, exposure to full-field visual
  environments during gaze tasks elicited some
  symptoms in persons with PVH, but was, in
  general, fairly well tolerated. Thus, motion
  sickness does not appear to be a limiting factor
  in the use of VR exposure therapy in patients
  with PVH.

• Subject Population
• Healthy Subjects
• Control subjects (n21 ages 22-83 mean 48,
  s.d. 19) with no otologic or neurologic disease
  participated.
• Exclusion criteria included a significant
  history of migraine, motion sickness, recent
  orthopedic injury in a weight bearing joint,
  plantarflexion contractures, use of an assistive
  device, abnormal age adjusted hearing, worse than
  20/80 acuity with either contacts or eyeglasses,
  a history of panic or anxiety disorder, or
  impaired distal sensation.
• Patients
• Six people with peripheral vestibular
  hypofunction (PVH, 3 right and 3 left age
  range-35-77 mean 57 s.d. 15) participated.
  One of the patients had an acoustic neuroma
  resection and the remaining 5 patients had
  peripheral vestibular disorders.
• Length of symptoms ranged from 4-14 months for
  those with hypofunction and 6 years for the
  person post-surgery.

• All participants rated their symptoms before the
  first trial and after each subsequent trial using
  Subjective Units of Discomfort (SUDs, Wolfe, 1982
  ) and Simulator Sickness Questionnaire (SSQ,
  Kennedy et al, 1993).
• The SUDs rating scale is based on the degree of
  overall discomfort or anxiety that the person is
  experiencing (0-10 scale).
• The SSQ requires subjects to rate the level of
  severity of 16 symptoms. The levels are
• 0 none, 1 slight, 2 moderate, and 3
  severe
• The SSQ has 3 subscales that are composed of the
  scores from 7 of the symptoms. Each subscale
  reflects a different dimension of simulator
  sickness Nausea, Disorientation, and Oculomotor
  stress (Table 3).
• A total score is also computed (SSQTotal)

• References
• Ring H. Is neurological rehabilitation ready for
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• Kennedy RS, Lane NE, Berbaum KS, Lilienthal ML.
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• Wolfe J. The Practice of Behavior Therapy.
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• Sparto PJ, Whitney SL, Hodges LF, Furman JM,
  Redfern MS. Simulator sickness when performing
  gaze shifts within a wide field of view optic
  flow environment preliminary evidence for suing
  virtual reality in vestibular rehabilitation. J
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• Cobb SV, Nichols S, Ramsey A, Wilson JR. Virtual
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• Severity of SUDs
• For each trial, the distribution of the severity
  of SUDs rating was determined for the controls
  and subjects with PVH
• The distribution of the severity of SUDs ratings
  was significantly different in controls and
  subjects with PVH (p lt 0.001). Subjects with PVH
  had more discomfort (Figure 3A).

• Experimental Methods
• Visual scene exposure was performed using the
  Balance Near Automatic Virtual Environment
  (BNAVE) system (Sparto et al, 2004). This system
  provides a full-field optic flow through
  back-projection on three contiguous screens
  (Figure 1).
• Subjects attended 6 sessions, approximately 1
  week apart. Subjects were exposed to six
  different optic flow conditions days 1 and 2
  had no optic flow, days 3-6 had optic flow of
  either high/low contrast and either low/high
  spatial frequency (Table 1).

Acknowledgement Supported by NIH grants DC005384,
DC05205, DC05372, and the Eye and Ear Foundation.
Special thanks to Leigh Mahoney, Theresa Yi, and
Jeffrey Jacobson.