Effects of Duration of Immersion in a Virtual Reality Environment on Postural Stability

Few studies have been carried out to examine the relation between postural stability and subjective reports or feelings of motion sickness. Two views seem to exist on the relation between immersion in a virtual reality (VR) environment and subjective feelings of motion sickness. One predicts that the immersion induces both postural instability and motion sickness. Another view is that preimmersion postural instability predisposes people to motion sickness. However, these views are not supported by empirical research. Longer immersions in a VR environment may induce higher levels of postural instability and symptoms of motion sickness. In this study, effects of long-hours immersion in a VR environment on postural stability were examined to approach the underlying mechanism of postural instability and motion sickness using force platform measurement and self-reported questionnaire on motion sickness. As a result, it was suggested that longer immersion in a VR environment induced postural instability and symptoms of motion sickness.     

Demand characteristics in assessing motion sickness in a virtual environment: or does taking a motion sickness questionnaire make you sick?

The experience of motion sickness in a virtual environment may be measured through pre and postexperiment self-reported questionnaires such as the Simulator Sickness Questionnaire (SSQ). Although research provides converging evidence that users of virtual environments can experience motion sickness, there have been no controlled studies to determine to what extent the user's subjective response is a demand characteristic resulting from pre and posttest measures. In this study, subjects were given either SSQ's both pre and postvirtual environment immersion, or only postimmersion. This technique tested for contrast effects due to demand characteristics in which administration of the questionnaire itself suggested to the participant that the virtual environment may produce motion sickness. Results indicate that reports of motion sickness after immersion in a virtual environment are much greater when both pre and postquestionnaires are given than when only a posttest questionnaire is used. The implications for assessments of motion sickness in virtual environments are discussed.     

Development of a balance analysis system for early diagnosis of Parkinson's disease

The purpose of this research is to develop a postural balance evaluation system using center-of-pressure (COP) analysis techniques for early diagnosis of Parkinson's disease (PD). A COP sensing device was developed, and applicable test protocols were proposed. Subsequently, posturographic parameters, which reflect the characteristics of postural control, were extracted to evaluate postural balance. Decisive indicators for postural stability were selected among the posturographic parameters through statistical validation based on clinical data. A discriminant function was then suggested to predict the existence of PD in patients. This clinical study consisted of 127 participating subjects. A validation study (n = 51, 40% of the overall data) using the discriminant function concluded with 100% accuracy that 37 healthy subjects did not have PD and 14 subjects with PD were correctly diagnosed.Relevance to industryPostural instability has become a critical issue since people with postural balance disorders are frequently exposed to the danger of falling and injuries. This paper provides a device, test protocol, and evaluation method to analyze postural balance and predict the existence of PD. We expect that our proposed system can be exploited for neurosurgery of PD patients, and other clinical medical fields such as rehabilitation, geriatrics, and orthopedics.     

Measurement of presence and its consequences in virtual environments

A sense of presence is one of the critical components required by any effective virtual environment (VE). In contrast, side effects such as sickness may be produced in some virtual environments, detracting from the enjoyment or usefulness of the VE and from subsequent performance of the participant. Both presence and sickness in virtual environments are multifactorial phenomena not easily amenable to understanding or measurement. The first experiment reported here compares use of direct performance measures and rating scales to assess presence, whilst varying the VE display medium (head mounted and desktop displays) and whether or not sound was used in the VE. The second experiment addresses associations between presence, sickness and enjoyment of virtual environment participation. There was enough comparability between a reflex response within the VE and the rating scales to justify future exploration of the former measure of presence. A number of explanations are given for the partial association found between presence and sickness.     

Recovery from virtual environment exposure: expected time course of symptoms and potential readaptation strategies

OBJECTIVE: This study investigated potential means of facilitating a return to normal functioning following virtual environment (VE) exposure using a peg-in-hole exercise in recalibrating hand-eye coordination, a targeted gait movement (rail walking) in recalibrating vestibular (i.e., postural) aftereffects, and natural decay. BACKGROUND: Despite technology advances and considerable efforts focused on the identification and quantification of VE aftereffects, few have addressed means for recuperation, the focus of the current study. METHOD: After 15 min-60 min of VE exposure and recalibratory exercises, hand-eye coordination and postural stability were assessed electronically, the former via a 3-D measure capturing pointing errors, and the latter by head and body oscillations while standing in the tandem Romberg position. Both measurements were collected immediately after VE exposure and every 15 min up to 1 hr thereafter. Results: Participants (more than 900 college students) who experienced the peg-in-hole readaptation strategy had a significant decrease (p < 0.000 in pointing errors following the exercise; the other two methods (i.e., rail walking, natural decay) showed no significant change. For posture, all groups showed significant improvement during the 15 minutes after VE exposure, yet none returned to baseline by 1 hr postexposure. CONCLUSION: Although hand-eye coordination readaptation strategies showed noticeable effects immediately after they were performed, aftereffects were not completely eliminated after 1 hr; hence further research on readaptation strategies is essential to achieve more substantial recalibratory gains in hand-eye coordination and posture. Additionally, hand-eye coordination and vestibular aftereffects may require a period exceeding the VE immersion time in order to recover. APPLICATION: These findings may serve as a guide in the development of monitoring policies following VE exposure.     

Height effects in real and virtual environments

The study compared human perceptions of height, danger, and anxiety, as well as skin conductance and heart rate responses and postural instability effects, in real and virtual height environments. The 24 participants (12 men, 12 women), whose average age was 23.6 years, performed "lean-over-the-railing" and standing tasks on real and comparable virtual balconies, using a surround-screen virtual reality (SSVR) system. The results indicate that the virtual display of elevation provided realistic perceptual experience and induced some physiological responses and postural instability effects comparable to those found in a real environment. It appears that a simulation of elevated work environment in a SSVR system, although with reduced visual fidelity, is a valid tool for safety research. Potential applications of this study include the design of virtual environments that will help in safe evaluation of human performance at elevation, identification of risk factors leading to fall incidents, and assessment of new fall prevention strategies.     

Manipulating Objects in Virtual Worlds: Categorization and Empirical Evaluation of Interaction Techniques

The acceptance of virtual environment (VE) technology requires scrupulous optimization of the most basic interactions to maximize user performance and provide efficient and enjoyable virtual interfaces. Motivated by insufficient understanding of human factors implications in the design of interaction techniques for object manipulation in virtual worlds, this paper presents results of a formal study that evaluated two basic interaction metaphors for virtual manipulation—virtual pointer and virtual hand—in object selection and positioning tasks. In this work, we survey and categorize current virtual manipulation techniques according to their basic design metaphors, conduct experimental studies of the most basic techniques, and derive guidelines to aid designers in the practical development of VE applications.     

The impact of self-efficacy and perceived system efficacy on effectiveness of virtual training systems

This study developed and tested a research model which examined the impact of user perceptions of self-efficacy (SE) and virtual environment (VE) efficacy on the effectiveness of VE training systems. The model distinguishes between the perceptions of one's own capability to perform trained tasks effectively and the perceptions of system performance, regarding the established parameters from literature. Specifically, the model posits that user perceptions will have positive effects on task performance and memory. Seventy-six adults participated in a VE in a controlled experiment, designed to empirically test the model. Each participant performed a series of object assembly tasks. The task involved selecting, rotating, releasing, inserting and manipulating 3D objects. Initially, the results of factor analysis demonstrated dimensionality of two user perception measures and produced a set of empirical validated factors underlining the VE efficacy. The results of regression analysis revealed that SE had a significant positive effect on perceived VE efficacy. No significant effects were found of perceptions on performance and memory. Furthermore, the study provided insights into the relationships between the perception measures and performance measures for assessing the efficacy of VE training systems. The study also addressed how well users learn, perform, adapt to and perceive the VE training, which provides valuable insight into the system efficacy. Research and practical implications are presented at the end of the paper.     

虚拟世界中的操纵技术研究进展II:对现有操纵技术的实验评价

随着VE技术日益被接受,在VE交互作用中如何最大地发挥操作者的作用将受到更多的关注。文章综述了沉浸式交互技术中最重要的问题之一:用于沉浸式对象选择和定位的交互技术,得到了一些通用性的VE界面的设计概念。     

Egocentric Object Manipulation in Virtual Environments: Empirical Evaluation of Interaction Techniques

The acceptance of virtual environment (VE) technology requires scrupulous optimization of the most basic interactions in order to maximize user performance and provide efficient and enjoyable virtual interfaces. Motivated by insufficient understanding of the human factors design implications of interaction techniques and tools for virtual interfaces, this paper presents results of a formal study that compared two basic interaction metaphors for egocentric direct manipulation in VEs, virtual hand and virtual pointer, in object selection and positioning experiments. The goals of the study were to explore immersive direct manipulation interfaces, compare performance characteristics of interaction techniques based on the metaphors of interest, understand their relative strengths and weaknesses, and derive design guidelines for practical development of VE applications.     

Efficacy of three interventions at mitigating the adverse effects of muscle fatigue on postural control

This study evaluated the efficacy of three interventions at reducing the adverse effects of muscle fatigue on postural control. The first provided rest breaks according to perceived decrements in postural stability, while the other two involved auditory stimulations (static pure tone and moving conversation). Sixteen participants performed repetitive box handling (lifting + lowering) over 1.5 h to induce muscle fatigue mainly in the lumbar extensors. Trials of quiet upright stance were completed at 10-min intervals, during which the interventions (or a control condition) were applied. Postural control was assessed using perceived stability (PS) and several measures derived from centre-of-pressure (COP) time series. Allowance of rest breaks did not significantly affect any of the objective measures, though a trend indicated an offset to fatigue-induced decreases in PS. Both the static pure tone and moving conversation led to significant changes in the dependent measures indicating a mitigation of fatigue-induced postural instability. PRACTITIONER SUMMARY: We examined the effects of three control strategies on postural control in the presence of muscle fatigue induced by a simulated occupational task. The findings can facilitate the development of future strategies or practical interventions to reduce falling risk and prevent falls.     

Postural instability and motion sickness in a virtual moving room

OBJECTIVE: We examined motion sickness in an oscillating virtual environment presented via a video projector system. BACKGROUND: Visible oscillation of the physical environment is known to induce both postural instability and motion sickness, but it cannot be assumed that the same phenomena will occur in a virtual simulation of such motion. METHOD: Standing participants (3 men and 9 women, 20-22 years of age) were exposed to oscillation of a virtual room. The stimulus was a computer-generated simulation of a laboratory device that is known to induce postural instability and motion sickness. Participants viewed the simulation for up to 40 min and were instructed to discontinue if they experienced symptoms of motion sickness. RESULTS: Motion sickness incidence (42%) did not differ from that in studies using the corresponding physical moving room. Prior to motion sickness onset, the sick group exhibited changes in movement, relative to the well group, as predicted by the postural instability theory of motion sickness. Differences in movement between the sick and well groups developed over time, in contrast with previous studies using physical moving rooms, in which such movement differences have not evolved. CONCLUSION: The results indicate that changes in postural activity precede motion sickness that is induced by an oscillating virtual environment, but they also reveal differences in postural responses to virtual and physical motion environments. APPLICATION: Potential applications of this research include recommendations for the use of virtual environments as models for perception and action in physical environments.     

Measuring the Sense of Presence and its Relations to Fear of Heights in Virtual Environments

This article describes a study in which a genuine effect of presence--the development of fear of virtual stimuli--was provoked. Using a self-report questionnaire, the sense of presence within this situation was measured. It was shown that fear increased with higher presence. The method, which involved 37 participants, was tested and validated with user tests at the Bauhaus University. A growing body of research in human-computer interface design for virtual environments (VE) concentrates on the problem of how to involve the user in the VE. This effect, usually called immersion or the sense of presence, has been the subject of much research activity. This research focuses on the influence of technical and technological parameters on the sense of presence. However, little work has been done on the effects of experienced sense of presence. One field in which a sense of presence is necessary for the successful application of VEs is the treatment of acrophobic patients. Our goals are to (a) create a theory-based self-report measurement for presence and (b) measure presence independently from specific effects to validate the measurement. The anxiety resulting from the confrontation with a virtual cliff is used to validate the measurement of presence.     

Brain activity and presence: a preliminary study in different immersive conditions using transcranial Doppler monitoring

Transcranial Doppler (TCD) sonography is a brain activity measurement technique that monitors the hemodynamic characteristics of the major cerebral arteries in normal and pathological conditions. As it is not invasive, it can be easily used in combination with virtual environments (VE). In the present study, TCD has been used to analyze brain activity variations in different presence conditions during the exposure to a VE. Forty-two subjects have taken part in the experience grouped in two different visualization conditions: a CAVE-like and a single screen projection configuration. In each session, two different navigation conditions were used: a free navigation (controlled by the subject) and an automatic navigation (controlled by the system). Results show that these immersion and navigation modifications in the VE generate changes in brain activity that can be detected using TCD techniques. Several factors, one of them being presence, could be having an influence on this behavior.     

Creation and evaluation of a multi-sensory virtual assembly environment

The multi-modal information presentation, integrated into the virtual environment （VE）, has potential for stimulating different senses, improving the user＇s impression of immersion, and increasing the amount of information that is accepted and processed by the user＇s perception system. The increase of the useful feedback information may reduce the user＇s cognitive load, thus enhancing the user＇s efficiency and performance while interacting with VEs. This paper presents our creation of a multi-sensory virtual assembly environment （VAE） and the evaluation of the effects of multi-sensory feedback on the usability. The VAE brings together complex technologies such as constraint-based assembly simulation, optical motion tracking technology, and real-time 3D sound generation technology around a virtual reality workbench and a common software platform. The usability evaluation is in terms of its three attributes： efficiency of use, user satisfaction, and reliability. These are addressed by using task completion times （TCTs）, questionnaires, and human performance error rates （HPERs）, respectively. Two assembly tasks have been used to perform the experiments, using sixteen participants. The outcomes showed that the multi-sensory feedback could improve the usability. They also indicated that the integrated feedback offered better usability than either feedback used in isolation. Most participants preferred the integrated feedback to either feedback （visual or auditory） or no feedback. The participants＇ comments demonstrated that nonrealistic or inappropriate feedback had negative effects on the usability, and easily made them feel frustrated. The possible reasons behind the outcomes are also analysed by using a unifying human computer interaction framework. The implications, concluded from the outcomes of this work, can serve as useful guidelines for improving VE system design and implementation.     

Use of physiological signals to predict cybersickness

Cybersickness is a common and unpleasant side effect of virtual reality immersion. We measured physiological changes that were experienced by seated subjects who interacted with a virtual environment (VE) first while viewing a display monitor and second while using a head-mounted display (HMD). Comparing results for these two conditions let us identify physiological consequences of HMD use. In both viewing conditions, subjects rated the severity of their symptoms verbally and completed a post-immersion cybersickness assessment questionnaire. In the HMD viewing condition but not in the display monitor condition, verbal reports of cybersickness severity increased significantly relative to baseline. Half of the subjects chose to exit the VE after six minutes of HMD use and reported feeling some nausea at that time. We found that changes in stomach activity, blinking, and breathing can be used to estimate post-immersion symptom scores, with R² values reaching as high as 0.75. These results suggest that HMD use by seated subjects is strongly correlated with the development of cybersickness. Finally, a linear discriminant analysis shows that physiological measures alone can be used to classify subject data as belonging to the HMD or monitor viewing condition with an accuracy of 78%.     

A VE framework to study visual perception and action

In the real world, vision operates in harmony with self-motion yielding the observer to unambiguous perception of the three-dimensional (3D) space. In laboratory conditions, because of technical difficulties, researchers studying 3D perception have often preferred to use the substitute of a stationary observer, somehow neglecting aspects of the action-perception cycle. Recent results in visual psychophysics have proved that self-motion and visual processes interact, leading the moving observer to interpret a 3D virtual scene differently from a stationary observer. In this paper we describe a virtual environment (VE) framework which presents very interesting characteristics for designing experiments in visual perception during action. These characteristics arise in a number of ways from the design of a unique motion capture device. First, its accuracy and the minimal latency in position measurement; second, its ease of use and the adaptability to different display interfaces. Such a VE framework enables the experimenter to recreate stimulation conditions characterised by a degree of sensory coherence typical of the real world. Moreover, because of its accuracy and flexibility, the same device can be used as a measurement tool to perform elementary but essential calibration procedures. The VE framework has been used to conduct two studies which compare the perception of 3D variables of the environment in moving and in stationary observers under monocular vision. The first study concerns the perception of absolute distance, i.e. the distance separating an object and the observer. The second study refers to the perception of the orientation of a surface both in the absence and presence of conflicts between static and dynamic visual cues. In the two cases, the VE framework has enabled the design of optimal experimental conditions, permitting light to be shed on the role of action in 3D visual perception.     

Effects of foot placement on postural stability of construction workers on stilts

Stilts are elevated tools that are frequently used by construction workers to raise workers 18-40 inches above the ground. The objective of this laboratory study was to evaluate the potential loss of postural stability associated with the use of stilts in various foot placements. Twenty construction workers with at least 1 year of experience in the use of stilts participated in this study. One Kistler™ force platform was used to collect kinetic data. Participants were tested under six-foot-placement conditions. These 6 experimental conditions were statically tested under all combinations of 3 levels of elevation: 0″ (no stilts), 24″ stilt height and 40″ stilt height. SAS mixed procedure was used to evaluate the effect of different experimental conditions. The results of the multivariate analysis of variance (MANOVA) and repeated measures of univariate analyses of variance (ANOVAs) demonstrated that stilt height, foot-placement direction, and foot-placement width all had significant effects on the whole-body postural stability. This study found that the higher the stilts were elevated, the greater the postural instability. A stance position with one foot placed forward of the other foot produced greater postural instability than a position with the feet parallel and directly beneath the body. This study found that placement of the feet parallel and directly beneath the body, with the feet positioned a half shoulder width apart, caused a greater amount of postural sway and instability than one and one-and-half shoulder width. This study also found that construction workers using the stilts could perceive the likely postural instability due to the change in foot placements.     

Integrating vestibular displays for VE and airborne applications

Designing effective human machine interfaces is one of the more challenging and exciting issues facing engineers today. Many virtual environment (VE) designers approach this problem by examining the way humans interact with their natural environment. In essence, they have attempted to mimic the various ways humans use their senses to gather information. This approach seeks to present task relevant information in a form that is familiar, compellingly realistic, and intuitive. We have taken this design approach for the development of a direct vestibular display. We intend to provide self motion information to the vestibular system in a static virtual environment-that is, to simulate not only the look but also the feel of such sensations as turning and swaying. The article explains our rationale and method for doing so and reports results from our experiments using a visual vestibular interface     

Predicting real-world ergonomic measurements by simulation in a virtual environment

Virtual reality techniques have been increasingly used for ergonomic applications. However, it is always important to know whether the results obtained in a virtual environment (VE) are representative of a real environment (RE) ones. This paper presents our preliminary experimental results on the relationship between ergonomic measurements in VE and RE for some typical “drilling” tasks. The same tasks were carried out by thirty male manufacturing factory workers in both VE and RE. Five evaluation indices - three objective (elbow angle, maximum force capacity reduction, and task completion time) and two subjective (BPD - Body Part Discomfort and RPE - Rated Perceived Exertion) - were used to evaluate the similarities between VE and RE for the selected “drilling” tasks. Four of these indices (all except elbow angle) were significantly higher (p < 0.05) in VE than in RE, which indicates that subjects experienced more discomfort and grew fatigued more quickly in VE. However, linear correlations (Pearson’s rho: 0.635-0.807) between VE and RE were found for two of the five indices (BPD and maximum force capacity reduction).

Relevance to industry

Using digital mock-ups and virtual reality simulations, industrial work activities can be evaluated to identify potential ergonomic problems during an early design stage, which reduces design time and costs, increases quality and improves customer satisfaction. A validated linear relationship can provide a reference for work design in virtual reality.