virtual reality as a rehabilitative tool for persons with vestibular disorders-preliminary findings...
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Virtual Reality as a Rehabilitative Tool for Persons with Vestibular Disorders-Preliminary Findings Whitney SL 1,2,4, Furman JM 1,2,3, Redfern MS 1,2,3, Sparto PJ 1,2, Jacobson J 5, Brown KE 6, Wrisley DM 2,3, Hodges L 7 1Department of Otolaryngology, 2Department of Physical Therapy, 3 Department of Bioengineering, University of Pittsburgh, 4Centers for Rehab Services, UPMC, 5Department of Library and Information Science, University of Pittsburgh, 6 Department of Physical Therapy, Duquesne University, 7 Department of Computer Science, Georgia Tech University Supported by NIH grant DC04784 and the Eye and Ear Foundation of Pittsburgh
DISCUSSION No subject experienced significant discomfort while
viewing the scene
Sinusoidal responses occurred at the same frequency as scene movement for both the COP measures and the head movement, indicating that normal individuals are affected by the visual scene movement
During the sinusoid trials, there was greater movement of the COP when the block size was 4 squares per meter compared to 2 squares per meter indicating that the size of the objects in the virtual world affect postural sway
CONCLUSIONS The BNAVE is a safe virtual environment for assessing
postural control responses
Head movement and COP can be recorded simultaneously with the virtual scene movement
Block size affects postural sway
ABSTRACT The use of medical virtual reality (VR) for rehabilitation in persons with balance disorders is a new concept introduced by Virre1 and Kramer et al2. The Balance Near Automatic Virtual Environment (BNAVE), a sophisticated PC-based visual display booth, has been created to assess and retrain balance in persons with vestibular disorders. The purpose of this study was to develop the appropriate software and hardware necessary to perform pre-clinical trials in persons without disease, and then to determine tolerance, treatment methodologies, and appropriate measures to adequately assess the efficacy of VR as a rehabilitative tool.
We report findings from 2 normal subjects. Both subjects were screened for neurologic and orthopedic disorders. Neither subject had a significant history of motion sickness. Each subject was exposed to a primitive checkerboard scene in the BNAVE and several parameters were manipulated including the apparent size, the brightness, the complexity/spatial frequency, and the movement of the scene. During exposure to each of the scenes heart rate, subjective units of discomfort, postural sway, facial expression, and eye/head position are monitored. Before and after exposure, postural sway, blood pressure, the Simulator Sickness Questionnaire, gait speed and the Dynamic Gait Index are assessed. Preliminary data indicate that subjects can tolerate the exposures and that the scene affected postural sway.
PURPOSETo collect preliminary postural data in persons without disease while exposed to a virtual reality moving scene
RESULTS
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
Persons with vestibular disorders have abnormally large, visually-induced postural responses
It is impossible to replicate visually complex visual environments in a traditional rehabilitation setting and control the input
SUBJECTSTwo persons participated in the preliminary study (ages 38 and 39-both females)
PROCEDURES Subjects removed their shoes, donned the head motion
sensor, and stood on a force platform with their feet comfortably apart (Figure 1)
They wore a harness secured to the support above them
Subjects viewed a “virtual tunnel” scene in a darkened room (Figure 2) at 0.1 Hz sinusoidal scene movement
Each subject viewed the visual scene for 60 seconds (10 seconds with the scene on but not moving, 40 seconds of scene movement, and 10 seconds without scene movement) and were asked about any discomfort that they experienced while viewing the scene
The BNAVE: Balance Near Automatic Virtual Environment
Viewing angle of 200 degrees horizontally and 90 degrees vertically (Figure 3)
Each display is produced by VREX 2210 LCD-based stereoscopic digital projectors controlled by an Intel PIII computer
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
DATA ANALYSIS We estimated the location of the center of pressure (COP) anterior-
posterior movement at the feet and the head (Figure 4A)
We computed the root-mean-square (RMS) values of COP and head movement for pre-, during, and post-movement of the scene (Figure 4B)
Figure 4. A) Head and center of pressure (COP) data obtained during sinusoidal scene movement at 0.1 Hz, 4 meters per second, and 4 squares per meter. B) RMS values of antero-posterior COP during the sinusoidal trials, according to block size and velocity of scene.
Right side projector
Front projector
Left side projector
Figure 1. Subject standing on the force platform in the BNAVE.
Figure 3. Layout of BNAVE showing the mirror configuration. Coordination of the projects to maintain the size of the scenes requires reflection by a mirror system for 2 of 3 projectors.
Figure 2. A view of the virtual tunnel.
FUTURE STUDIES Plan to study the effect of varying the velocity of the scene
on location and RMS values of the COP
Plan on testing older adults and young persons to determine if there is an age effect
REFERENCESViirré E In Heath Care in the Information Age. Sieburgh H, Weghorst S, Morgan K. Studies in Health Technology Informatics. Vol 29. Vestibular Telemedicine and Rehabilitation Applications for Virtual Reality, 1996a
Viirré E. Virtual reality and the vestibular apparatus. IEEE Engineering in Medicine and Biology. 1996b;2:41-43, 69.
Viirré E. Micromedical technologies vestibular update. 2000;24:1-4.
Kramer PD, Roberts DC, Shelhamer M, Zee DS. A versatile stereoscopic visual display system for vestibular and oculomotor research. J of Vestibular Research 1998;8:363-379.
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