1. Symptom Expression during Virtual Reality Exposure Susan L. Whitney 1,2, Patrick J. Sparto 1,2,3, Larry Hodges 4, Joseph M. Furman 1,2, and Mark S. Redfern 1,2,3 Departments of 1 Otolaryngology, 2 Physical Therapy, and 3 Bioengineering, University of Pittsburgh, Pittsburgh, PA and the 4 University 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, p<0.001) for all measures. The percentage of trials in which some symptoms occurred in the control and vestibular groups (CON:PVH) were as follows: SUDS: (19%:55%); SSQ total: (25%:57%); SSQ nausea: (12%:40%); SSQ disorientation: (5%:50%); and the SSQ oculomotor: (24%:51%). Conclusion: Patients with vestibular disorders appear to experience more discomfort than controls during virtual reality immersion. 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. Acknowledgement Supported by NIH grants DC005384, DC05205, DC05372, and the Eye and Ear Foundation. Special thanks to Leigh Mahoney, Theresa Yi, and Jeffrey Jacobson. References -Ring H. Is neurological rehabilitation ready for ‘immersion’ in the world of virtual reality? Disabil Rehabil 1998;1:61-74 -Kennedy RS, Lane NE, Berbaum KS, Lilienthal ML. Simulator sickness questionnaire: an enhanced method for quantifying simulator sickness. International Journal of Aviation Psychology. 1993;3:203- 220. -Wolfe J. The Practice of Behavior Therapy. Pergamon Press, 1982. -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 of NeuorEngin and Rehabil. 1:1-14, 2004. -Cobb SV, Nichols S, Ramsey A, Wilson JR. Virtual reality induced symptoms and effects (VRISE). Presence Teleoperators and Virtual Environments. 1999;8(2):169-186. Subject Population Healthy Subjects: Control subjects (n=21; 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. 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 > 0 SSQ:Total and subscales 0: assigned if subject reported 0 for all items in subscale or total 1: assigned if subject reported >0 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 χ 2 test (p < 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. 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. 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). 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. 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 (SSQ:Total) Table 1. Stationary scene or optic flow conditions for each of the six visits. During visits 3-6, Conditions C-F were randomized. Visit Condition Optic Flow Contrast Spatial Frequency 1 A No NoneNone (solid gray) 2 B No HighHigh 3 C Yes LowLow 4 D Yes LowHigh 5 E Yes HighLow 6 F Yes HighHigh Table 2. Eight gaze tasks were performed on each visit (6 visits). The order of the gaze tasks was randomized on trials 3-8 of each visit. TrialGaze Task 110 degree head saccades to the right (calibration) 2Control task- no head or eye movement (look straight ahead) 3Head looking straight, eye saccades +/- 10 degrees 4Head left 50 degrees, eye saccades +/- 10 degrees 5Head right 50 degrees, eye saccades +/- 10 degrees 6Gaze stabilization during 0.25 Hz sinusoidal head movements 7Gaze saccades to ± 40 and ± 50 degrees from midline 8Smooth pursuit to the left from 10-60 degrees, then to the right Table 3. Simulator Sickness Questionnaire (SSQ) Subscales SSQ: Nausea SSQ: Disorientation SSQ:Oculomotor General discomfortNausea Eyestrain NauseaHead fullness Headache Stomach awarenessBlurred vision Fatigue SweatingDifficulty focusing General discomfort Difficulty concentrateDizzy:eyes open Blurred vision BurpingVertigo Difficulty focusing Increased salivationDizzy:eyes closed Difficulty concentrating Figure 1. Examples of the VR scenes with high (left) and low (right) spatial frequency. Figure 3. A) The distribution of the the severity of SUDs ratings for controls (CON) and subjects with PVH. B) The distribution of the number of SSQ symptoms that were reported by controls and and subjects with PVH. AB Figure 2. Percentage of all trials with ratings greater than 0 for Subjective Units of Discomfort (SUDs) and the Simulator Sickness Questionnaire (SSQ) subscales and total. CON: controls, PVH: peripheral vestibular hypofunction 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 > 0, within each subscale and in total. The tasks elicited a a greater number of symptoms in subjects with PVH compared with controls (p < 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. 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 < 0.001). Subjects with PVH had more discomfort (Figure 3A).