1993 VR Conference Proceedings

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Determining Physiological Effects Of Using VR Equipment

Russell C. Eberhart and Paul N. Kizakevich
Research Triangle Institute
P. O. Box 12194
Research Triangle Park, NC 27709

Abstract

Work-in-progress at Research Triangle Institute (RTI) is reviewed that is seeking to establish baselines for quantifying biomedical effects of VR system components, including cardiac physiology and performance measurements of subjects performing VR-related tasks. Examples of effects that are being considered are physiological effects on the ocular, vestibular and neuromuscular systems, and psychological effects due to disorientation and confinement.


Introduction

Virtual reality (VR) and augmented reality (AR) systems are beginning to emerge from the laboratory and move into mainstream scientific, military, industrial and commercial applications.

Applications include such diverse areas as rehabilitation engineering and manufacturing assembly lines. As VR/AR becomes more common in the workplace, the potential health and performance effects of regular VR useage need to be defined. Causes of these potential effects include electric fields, magnetic fields, and physical forces and torques.

Examples of potential effects are physiological effects on the ocular, vestibular and neuromuscular systems, and psychological effects which might be triggered by conditions such as disorientation or confinement. For example, wearing a head-mounted display (HMD) will increase physical work and limit effective aerobic capacity. Performing tasks in the virtual environment may require increased sensory processing, cognition, vigilance, and concentration over similar tasks in the natural environment.

Such physiological requirements will likely affect blood catecholamines, heart rate, ventilation, cardiac contractility, and blood pressure. Individuals with hypertension or cardiac disease, whether evident or asymptomatic, could be adversely affected by repeated exposure to such stressors. Likewise, individuals with epilepsy may be adversely affected by exposure to visual and/or electrical stimuli at or near frequencies associated with human neural activity. These physiological responses may be insignificant in some individuals (non-responders) and very significant in others (responders). Conversely, regular use of some kinds of VR/AR technology may present little or no adverse health effects.


Objectives

RTI is seeking to establish and standardize methods and baselines for quantifying biomedical effects of VR/AR system components, including cardiac and neural physiology and performance measurements of subjects doing lower body and/or upper body exercise while performing VR/AR-related tasks.

The work being done by RTI falls into two general categories. The first category is investigating the physical sources of potential effects. Included is measuring the electric and magnetic fields, and the physical forces and torques, generated by VR/AR devices.

Also included is a hazard analysis of VR/AR devices from a more traditional safety standpoint, such as evaluation of potential for electrical shock. Devices to be evaluated include head-mounted displays (HMDs), navigation/positioning systems, and other input/output devices such as gloves and 3D mice.

The second category is investigating the physiological and psychological effects of using the VR equipment. Included is measurement of ECG, EEG, beat-to-beat blood pressure, cardiac function, skin resistance and core body temperature during execution of standardized tasks performed both while using and not using the VR/AR equipment.


Methodology

RTI has two major resources that are being utilized in this work: the RTI Virtual Reality Applications Laboratory and the RTI Human Studies Facility.

The Virtual Reality Applications

Laboratory contains a range of hardware from a Silicon Graphics Reality Engine, to an IBM RISC-6000, to personal computers. Several software systems are available, including IBM's Distributed Environment Construction Kit, which is a modular, object-oriented system that allows system modules to be flexibly connected, and allows the system to be run remotely, with only graphics rendering being done on the "local" machine.

The Human Studies Facility (HSF) is a dedicated facility for studying the physiological responses of human subjects to a variety of stresses that include heat, humidity, exercise and potentially toxic gases. This facility provides controlled temperature, humidity and air flow through a 10 x 10 x 8-foot chamber, into which controlled concentrations of gaseous and volatilized materials can be introduced. The facility supports both short-term (hours) and long-term experiments without requiring the subject to exit the controlled atmosphere.

The principal components of the HSF are the environmental exposure chamber, an airlock/changing room with sink, toilet and shower, the subject preparation area, the monitoring instrumentation area, the blood and laboratory analysis area, and the chamber airconditioning equipment. The facility has a variety of major subsystems for physiological and physical measurements, signal acquisition and processing, and other experiment data collection. Each subsystem has a dedicated computer workstation and all are linked via an Ethernet local area network. The subsystems are organized according to primary data processing functions: chamber environmental control, pollutant dosing control, pulmonary data acquisition, breath sounds data acquisition and analysis, experiment control and cardiac/neurologic data acquisition, and subject database and pollutant dose modeling subsystem.

To establish a VR/AR research capability in the HSF, RTI is installing an IBM RISC/6000 workstation with a graphics accelerator card and Crystal Eyes display. This will provide inexpensive X-windows access over the local area network for both development and execution of VR/AR applications using the IBM VR software system.

To develop experience in VR/AR technology, a set of VR/AR psychological tests are being developed. Each test is to be operative in either 2D or 3D-stereo. These include tracking tasks requiring the subject to follow a moving (random or patterned) object via a VR/AR input device such as a 3D-mouse or glove; and a vigilance task requiring the subject to respond manually to an event (such as sighting a specified object) interspersed among other random events. Such tasks are routinely used to study cognitive activity and cardiovascular responses in experimental subjects and patients. (For example, the Army has used such tasks to evaluate the effects of carbon monoxide exposure on cognitive performance.)

Investigation of VR/AR health effects includes the physical forces and torques associated with HMDs. Electromagnetic field measurements are being made on at least two HMDs at RTI's facility and at the facility of a corporate sponsor. Ergonomic effects of HMD usage are being investigated by cardiovascular measurements taken at rest and while performing a VR/AR-related activity with and without using the display. Measurements include heart rate, blood pressure, cardiac contractility, cardiac output, system vascular resistance, oxygen consumption, and carbon dioxide production. Calculations will be made of physical forces and torques experienced by HMD users over time.

The potential for psychological stress testing via the VR/AR environment will be evaluated by several methods. Up to ten subjects recruited from RTI staff will perform the VR/AR psychological tests and participate in a VR/AR stressful experience such as watching a rapid landscape fly-by in a virtual environment. Subjects will be monitored for cardiovascular measurements as described above. If possible, each subject will participate in both a 2D CRT and 3D-stereo VR environment.

The combination of RTI's HSF, experience in noninvasive measurements and VR capability significantly enhances the work being done. Any procedure involving psychophysiological effects is easily affected by environmental variables such as noise, temperature, etc. The ability to isolate the subject and control the environment should yield more productive studies than at many other potential sites. RTI's comprehensive set of noninvasive instrumentation is ideally suited for investigating the psychophysiological effects of VR/AR on cardiovascular and neurological variables.

The work being carried out is being supported by RTI Internal Research and Development funding (Project R853001) and by a corporate sponsor.


Clinical Applications

While recognizing the potential for health effects, RTI also envisions that VR will have clinical applications that act as vehicles to induce controlled physiological responses. Clinical diagnostic procedures often use physical or psychological stressors to induce expected and measurable physiological responses. For example, a healthy person will increase cardiac function during treadmill exercise while presenting no significant change in ECG waveshape; however, a person with cardiac disease will fail to increase cardiac function and show certain known changes in ECG waveshape.

Psychological stress tests, such as subtracting a series of numbers or writing an essay in a short period of time, are used to diagnose cardiac reactivity, a risk factor for hypertension.

When possible, stress tests are given to individuals prior to major surgery to qualify a patient's cardiovascular system for the stress of general anesthesia. Unfortunately, many subjects (i.e. cancer patients, orthopedic patients, paraplegics, etc.) are not able to perform such tests and the decision to proceed with surgery is made subjectively. A standardized psychological stress test using VR/AR technology could be a useful addition to the repertoire of stressors available for these evaluations.


Discussion

RTI has just begun the work described herein. Two preliminary baseline tests have been run.

The first test was a tracking task performed by a subject seated at a high-resolution display driven by a Silicon Graphics Onyx. The task was to navigate with a 2D mouse through "Performer Town," once at relatively low speed and once at relatively high speed. A suite of physiological measures was made, including ECG, EEG, beat-to-beat blood pressure, cardiac contractility, cardiac output, systemic vascular resistance, and respiration.

The second task was a tracking task performed by a subject on a treadmill. The task was to keep a Power Glove within a 3D cube in space about 80 mm on a side while walking on the treadmill. The treadmill was run at two speeds. During one part of the test, the subject received both visual and aural feedback on his performance. During another part of the test, the subject received only delayed aural cues. Physiological measures were made using the U. S.

Army's Biomedical Field Monitoring System, for which RTI is the systems integrator. This is a portable system that telemeters data to a remote receiver/computer station, so the subject is untethered. Parameters usually monitored by the system are core body temperature, skin temperature, skin resistance, heart rate and activity level.

Only a few experimental runs have been made, so our observations are anecdotal. It is interesting to note that the blood pressure of the subject doing the first task increased at the higher navigation speed, while cardiac output dropped over the duration of the test. It is not yet known whether these results are meaningful (they may not be repeatable). The drop in cardiac output could possibly be explained by the fact that the subject was seated for an extended period of time (about two hours).

As this work proceeds, it seems inevitable that more questions than answers will be generated. Many interesting questions exist now. For example, it is known that certain values of lag time in a visual display generate disorientation and "simulator sickness".

These lag times seem to be correlated with alpha and beta frequencies in brain activity. Is there, indeed, a correlation? It is hoped that these, and other, questions will be answered by RTI's biomedical team.

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