1 humanfactorsissuesin universityofcentralflorida...

Kay M Stanney1

University of Central FloridaDepartment of Industrial Engineeringand Management SystemsOrlando FL 32816

Ronald R MourantNortheastern UniversityDepartment of Industrial Engineering

and Information SystemsBoston MA

Robert S KennedyRSK Assessments Inc

Orlando FL

Human Factors Issues inVirtual EnvironmentsA Review of the Literature

Abstract

Virtual environments are envisioned as being systems that will enhance the communi-cation between humans and computers If virtual systems are to be effective and well

received by their users considerable human-factors research needs to be accom-plished This paper provides an overview of many of these human-factors issues in-cluding human performance efficiency in virtual worlds (which is likely inuenced bytask characteristics user characteristics human sensory and motor physiology multi-modal interaction and the potential need for new design metaphors) health and

safety issues (of which cybersickness and deleterious physiological aftereffects maypose the most concern) and the social impact of the technology The challenges eachof these factors present to the effective design of virtual environments and systematicapproaches to the resolution of each of these issues are discussed

1 Introduction

Efforts to apply virtual reality (VR) technology to advance the fields ofmedicine engineering education design training and entertainment are cur-rently underway The medical profession has expressed its desire to use VR sys-tems as training tools (Stytz Frieder amp Frieder 1991) human-factors special-ists are using VR for user-system analysis and design (Scott 1991) scientists areutilizing VR to visualize complex data (Defanti amp Brown 1991) stock marketanalysts want to use VR to predict market trends and achieve financial gains(Coull amp Rotham 1993) and the military currently uses VR to carry out vir-tual war scenarios and training exercises (Dix Finlay Abowd amp Beale 1993)Interest in this technology is so widespread that the US government asked theNational Research Council to identify and determine US VR research priori-ties (Adam 1993 Durlach amp Mavor 1995)

The reality is however that a considerable amount of systematic researchmust be carried out in order for VR to fulfill its potential Researchers need tofocus significant efforts on addressing a number of human factors issues if VRsystems are to be effective and well received by their users Perhaps this needwas best articulated by Shneiderman (1992) who stated that lsquolsquoanalyses of VRuser-interface issues may be too sober a process for those who are enjoyingtheir silicon trips but it may aid in choosing the appropriate applications and

Presence Vol 7 No 4 August 1998 327ndash351

r 1998 by the Massachusetts Institute of Technology

1Requests for reprints should be sent to Kay M Stanney University of Central Florida Depart-ment of Industrial Engineering and Management Systems Orlando FL 32816-2450 USA

Stanney et al 327

refining the technologiesrsquorsquo (p 224) We believe human-factors practitioners can assist in making significant con-tributions to the theoretical understanding of human-virtual environment interaction (HVEI) This paper hasorganized the area of human factors research in virtualenvironments (VEs) into three primary subtopics hu-man performance efficiency in virtual worlds health andsafety issues and potential social implications of VEtechnology (See Figure 1) Some of these topics havebeen looked at rather briefly in the past (Thomas amp Stu-art 1992) The objective of the present paper is to pro-vide a comprehensive overview of each of these humanfactors research areas and to provide insight into ap-proaches for their systematic resolution

Designing usable and effective interactive virtualworlds is a new challenge for system developers and hu-man-factors specialists Due to the close bond betweenthe user and the system within VEs it may be impossibleto follow past traditions and segregate human factorsfrom design issues when striving to achieve the potentialof VE technology It is the capabilities and limitations ofthe user that many times will determine the effectivenessof virtual worlds (See Figure 2) An understanding ofhuman-factors issues can thus be used to provide a sys-tematic basis by which to direct future VE research ef-forts aimed at advancing the technology to better meetthe needs of its users In the following sections threeprimary areas of human-factors research in VEs will be

addressed and issues requiring further research will beidentified

2 Human Performance Efficiencyin Virtual Worlds

Computer speed and functionality image process-ing synthetic sound and tracking mechanisms havebeen joined together to provide realistic virtual worldsA fundamental advance still required for VEs to be effec-tive is to determine how to maximize the efficiency ofhuman task performance in virtual worlds In manycases the task will be to obtain and understand informa-tion portrayed in the virtual environment As Wann andMon-Williams (1996 p 845) stated in such cases lsquolsquothegoal is to build (virtual) environments that minimize thelearning required to operate within them but maximizethe information yieldrsquorsquo Maximizing the efficiency of theinformation conveyed in VEs will require developing aset of guiding design principles that enable intuitive andefficient interaction so that users can readily access andcomprehend data The design approach used for moretraditional simulation systems (eg teleoperated sys-tems) was generally lsquolsquotrial and errorrsquorsquo due to the paucityof general non-system-specific design guidelines (Bur-dea amp Coiffet 1994) If VE tasks are designed in suchan ad hoc manner however the potential benefits of the

Figure 1 Areas of human-factors research for virtual environmentsFigure 2 The human factor in virtual environments

328 PRESENCE VOLUME 7 NUMBER 4

virtual world such as enhanced understanding andtransfer of training may be compromised While it isdifficult to gauge the importance of the various human-factors issues requiring attention it is clear that if hu-mans cannot perform efficiently in virtual environmentsthereby compromising the effectiveness of the HVEI orthe transfer of training then further pursuit of this tech-nology may be fruitless

In order to determine the effectiveness of a VE ameans of assessing human performance efficiency in vir-tual worlds is first required This is easier said than doneIn contrast to past HCI studies VE performance mea-sures need to focus on more than task outcome to beeffective Due to the complex nature of HVEI it may beessential to develop effective multicriteria measures toevaluate human performance in virtual environmentsFactors contributing to human performance in VEs pre-dictably include the navigational complexity of the VEthe degree of presence provided by the virtual worldand the usersrsquo performance on benchmark tests (SeeFigure 3)

If individuals cannot effectively navigate in VEs thentheir ability to perform required tasks will be severelylimited Wann and Mon-Williams (1996) have discussedthe edge and object information as well as the dynamicglobal changes in features and textures that are necessaryto achieve effective navigational performance Beyonddetermining such design principles that specify the nec-

essary cues to support navigation a designer must deter-mine how a user should move about a virtual worldWhile some developers have incorporated lsquolsquovarious per-mutations of windowing to allow people to moversquorsquoabout VEs (Laurel 1994) newer designs such as por-tals spirals sliders and tow planes hold promise for en-hanced VE interaction Nilan (1992) has explored themapping of a userrsquos cognitive space to the design of theVE to enhance navigational performance Darken andSibert (1996) have developed mediators and modalitiesto assist with VE navigation These approaches are likelyto achieve varying degrees of success prior to focusingon standard(s) for VE navigation

Due to the current issue of users becoming lost inconsiderably less-complex hierarchical computer envi-ronments (Sellen amp Nicol 1990) the design and devel-opment of standardized navigational techniques thatassist individuals in maintaining spatial orientationwithin VEs may prove to be one of the most importantissues to resolve in VE design (Darken amp Sibert 1996)Without adequate means of moving about VEs develop-ers cannot expect to maximize human performance Onepotential approach to addressing this issue is to developa means of measuring the lsquolsquonavigational complexityrsquorsquo of aVE (ie how challenging it is to move from point A topoint B) Such a measure would likely be dependent onthe sensorial cues and spatial mediators (eg maps) pro-vided by an environment as well as on the spatial abilityof the navigator Navigational complexity likely variesbetween VE designs and even within a given VE thuspotentially becoming a diagnostic tool for evaluating theeffectiveness of a given VE design (eg redesign couldbe directed to areas with high navigational complexity)Mental maps (Siegel 1981) wayfinding (Vishton ampCutting 1995) dead reckoning (Gallistel 1990) hom-ing (Adler 1971) spatial orientation (Adolfson ampBerghage 1974 Thorndyke amp Statz 1980) time tocollision (Lee 1976) geographical orientation (Clark ampMalone 1952) and vestibular functions (Howard1984) are a few of the fields with technical knowledgeregarding the perceptual issues involved with navigationin virtual environments Most researchers of these aboveareas have not yet adapted their knowledge to virtualenvironments When they do the field of perception is

Figure 3 Components of human performance in virtual environments

Stanney et al 329

likely to explode because VEs which can be manipulatedto present an infinite number of perceptual experiencesoffer an experimental paradigm to study perception thatis far superior to the prism spectacle of 100 years agoThese environments may provide the necessary tools toassist researchers in disclosing the mysteries of humanperception (Findlay amp Newell 1995) For example asimulated visual auditory or haptic stimulus could bemanipulated to determine the relative importance ofdifferent types of cues

The degree of presence experienced by an individualmay influence human performance (Fontaine 1992Zeltzer 1992) Presence is a factor of both the vividnessof an experience and the level of interaction (Sheridan1992 Steuer 1992) It is commonly considered thatoperation of a VE system that provides a high degree ofpresence is likely to be better accomplished than onewhere such perceptions are not present Little or no sys-tematic research is available however to substantiatethis assumption This may be due to the lack of system-atic methods for evaluating and defining the presencerequirements for different applications It is also likelythat this lack of information is related to the inadequatemanner in which human performance is measured(Lane 1986) At present presence is generally evaluatedvia either questionnaires (Hendrix amp Barfield 1995Singer Witmer amp Bailey 1994) or through as yet non-validated analytical models (Slater amp Usoh 1993) Adesirable goal would be to develop operational modelsof presence with objective measures that could assist indetermining the appropriate level of vividnessfidelityand interaction required for a given set of task character-istics It will also be necessary to have solid measures ofhuman performance in order to show that more pres-ence leads to better performance

The ability of an individual to effectively complete aset of VE benchmark tests may also influence perfor-mance (Burdea et al 1994) These tasks would includebut are not limited to the ability to move about the vir-tual world (ie move forward and backward move upand down turn etc) manipulate or track virtual ob-jects locate virtual sounds respond to kinesthetic forcefeedback or perform visual tasks (ie perceive and dis-criminate colors judge virtual distance search for rec-

ognize and estimate the size of virtual objects) Re-cently Lampton Knerr Goldberg Bliss Moshell andBlau (1994) have developed the Virtual EnvironmentPerformance Battery (VEPAB) The VEPAB includesthe determination of visual acuity locomotion abilityobject manipulation ability tracking ability and reactiontime while viewing virtual worlds The VEPAB is a movetoward benchmarking VE performance This batteryneeds to incorporate higher-level skills (eg a userrsquosnavigational ability) as well as multisensory benchmarksfor the auditory and kinesthetic senses to provide amore-comprehensive assessment of HVEI performanceThe results from such tests could provide a baseline fromwhich to judge the effectiveness of a VE For example ifthe evaluation of a VE led to low baseline data onewould not expect high user task performance from suchan environment In such cases usersrsquo task performancewould be limited by their inability to function operation-ally in the virtual world

Once a comprehensive set of factors influencing hu-man performance in VEs has been established moredefinitive studies of HVEI can be conducted Humanperformance in VEs will likely be influenced by severalfactors including task characteristics user characteristicsdesign constraints imposed by human sensory and mo-tor physiology integration issues with multimodal inter-action and the potential need for new visual auditoryand haptic design metaphors uniquely suited to virtualenvironments In order to maximize human perfor-mance in VEs each of these factors must be considered

21 Task Characteristics

One important aspect that will directly influencehow effectively humans can function in virtual worlds isthe nature of the tasks being performed Some tasks maybe uniquely suited to virtual representation while othersmay not be effectively performed in such environments

To justify the use of VE technology for a given taskwhen compared to alternative approaches the use of aVE should improve task performance when transferredto the real-world task because the VE system capitalizeson a fundamental and distinctively human sensory per-ceptual information-processing or cognitive capability


It is important to determine the types of tasks for whichthese types of benefits can be obtained by using VEtechnology Wann and Mon-Williams (1996) have sug-gested that data and feature analyses (eg dimensionalassessment visual detail enlargement design envision-ing contingency evaluation) and data visualization areviable tasks for gleaning such benefits Viable tasks canbe systematically specified by obtaining an understand-ing of the relationship between task characteristics andthe corresponding VE characteristics (ie stereoscopic3-D visualization real-time interactivity immersionmultisensory feedback) that effectively support their per-formance both within the VE and upon transfer to thereal-world task

Some evidence of the benefits of stereoscopic visual-ization comes from work by Kim Tendick and Stark(1993) In investigating the benefits of stereo cues in avirtual pick-and-place task they found that a stereo-scopic display was far superior to a monoscopic displayInterestingly however performance with the mono-scopic display was just as effective as the stereoscopicdisplay when visual perspective display enhancementswere provided (ie ground grids and projection lines)Similar benefits from stereo were demonstrated by Wick-ens Merwin and Lin (1994) Pepper Smith and Cole(1981) have also found that stereoscopic display perfor-mance is generally superior to monoscopic performancehowever they found the extent of improvement was de-pendent on the task visibility and learning factors Kimet al (1993) suggest that for simple telemanipulationtasks monocular depth cues and cognitive cues (accu-mulated through learning and past experiences) may besufficient for effective performance They argue thatwhen tasks become more complex and the monocularand cognitive cues provided are insufficient or lackingstereoscopic cues will enhance performance These sug-gestions may explain why Kozak Hancock Arthur andChrysler (1993) found no significant transfer-of-trainingbenefits from virtual reality training as compared toreal-world and no training conditions on a pick-and-place task The task used in this experiment picking up acan and placing it in a target location was one whichsubjects would have had many cognitive cues from pastexperience (eg from picking up soda cans or drinking

glasses) Therefore the additional stereoscopic cues pro-vided during the VR training trials may not have signifi-cantly added to the learnersrsquo performance on the task

Evidence of transfer from VR training of navigationaltasks (ie building navigation) has been found by Re-gian and Shebilske (1992) Based on the results of Kimet al (1993) it may be suggested that the navigationaltasks used in this study may have been more complex orless familiar than the pick-and-place tasks used by Kozaket al (1993) thus leading to performance benefits pro-vided by the additional stereoscopic cues Additionalstudy is needed to determine how to enhance transfer oftraining via VE training this will be predictably ante-dated by the determination and selection of appropriatetasks to train

While the benefits of interactivity and immersion toboth performance and presence are often cited (Burdeaet al 1994 Kalawsky 1993 Steuer 1992) little directempirical evidence exists Proffitt and Kaiser (1995) per-formed an experiment that demonstrated the benefits ofinteractivity In this experiment subjects standing infront of a hill judged its incline under three conditionsverbal visual (using a hand-held modified compass toapproximate the angle) and haptic (placing their handson a board and moving the board until its position ap-proximated the angle) Through the interactivity of thehaptic condition subjects were able to lsquolsquofeelrsquorsquo the anglewhich resulted in significantly better performance thanthe other conditions Benefits of interactive displays inmedicine such as the ability to interactively explorecomplex spatial and temporal anatomical relationshipshave also been cited (McConathy amp Doyle 1993 Meyeramp Delaney 1995 Wright Rolland amp Kancherla 1995)In fitness performance highly interactive exercise envi-ronments have been shown to produce significantlymore mechanical output (ie greater RPM total calo-ries burned and calories burned per minute) and pro-mote greater and more consistent participation than lessinteractive environments (Cherry 1995)

While these early studies provide evidence for the ben-efits of interactivity future research will need to addressthe types and levels of interactivity that are best suited togiven task profiles For example Williams Wickens andHutchinson (1994) found that interactivity had a differ-

Stanney et al 331

ential effect that was dependent on task workload Inthis study interactivity enhanced human performance ona navigational training task under normal workload con-ditions When the workload was increased and mentalrotation demands were recruited to orient a fixednorth-up map however individuals trained in the inter-active condition performed less effectively than thosewho studied a map This suggests that interactivity isbeneficial to the extent that it is maintained within hu-man information-processing limitations (Card Moranamp Newell 1983) Thus the benefits of interactivityshould not be universally assumed Designers shouldrecognize that interactivity brings with it increasedworkload demands that could negate its ability to en-hance human performance

The benefits of immersion have even less empiricalsupport than interactivity Esposito (1995) attempted toempirically verify the benefits of immersion using apuzzle construction task however no definitive conclu-sions about immersion could be drawn Although thereis limited direct empirical evidence to support the ben-efits of immersion considerable indirect evidence existsGreeno Smith and Moore (1993) for example suggestthat knowledge of how to perform a task is embedded inthe contextual environment in which the task is to beperformed and is not an independent property availablefor any situation Druckman and Bjork (1994) furthersuggest that only when a task is learned in its intendedperformance situations can the learned skills be used inthose situations Thus learners are thought to use envi-ronmental contextual cues to support and mediate theirtask actions Further transfer of training theories sug-gest that positive transfer increases with the level oforiginal learning as long as structurally similar stimuliand responses are available and required for both thetraining and transfer tasks (Schmidt amp Young 1987)The implication is that if virtual environments immerselearners in environments similar to the intended taskenvironments it follows that VE training should pro-mote more original learning and greater positive trans-fer Further study is indicated to empirically verify thebenefits of immersion in virtual environments One issueis how to isolate the benefits of immersion to immerseindividuals in a VE exposes them to 3-D stereoscopic

views and interactivity with virtual objects Thus thebenefits of stereo and interactivity must be factored outbefore the benefits of immersion can be determined Toadd to this difficulty it is well known that more practiceleads to improved learning Thus when studying factorssuch as immersion how does one equilibrate trainingtime in the experimental (VE) and control system Isrun time per se the controlling factor Or is it numberof training trials If these are not possible how else canexperimental factors be controlled to minimize con-founding effects This is an age-old problem in behav-ioral science but it should not be overlooked whencomparing human performance using different tech-nologies It is essential to control for such factors so thatit is not erroneously concluded that human performanceis enhanced by immersion (or other factors) when theimproved VR performance is directly related to the factthat subjects received more training time or trainingtrials

22 User Characteristics

An important aspect influencing human VE per-formance is the effect of user differences These differ-ences to provide a simplified analysis can be with theinput (eg interpupilliary distance) throughput (egcognitive or perceptual styles) or output (ie humanperformance) Significant individual performance differ-ences have already been noted in early VE studies(Lampton et al 1994) User characteristics that signifi-cantly influence VR experiences need to be identified inorder to design VE systems that accommodate theseunique needs of users User differences have alreadybeen reported to influence the sense of presence (Bar-field amp Weghorst 1993) and cybersickness experiencedby VE subjects (Parker amp Harm 1992) What is not asobvious are which user characteristics have a subtle im-pact and which substantially alter virtual experiences

In order to determine which user characteristics maybe influential in VEs one can examine studies in human-computer interaction (HCI) While both HCI andHVEI involve human-computer interaction due to dif-ferences between them (ie HCI is generally from anexocentric frame of reference while HVEI is generally


from an egocentric perspective) earlier HCI studies maynot directly apply to HVEI but can provide potentialinsights A significant amount of research has focused onunderstanding the influences of user characteristics inHCI (For a summary of a number of notable studiessee Egan 1988) Even though important this researchhas yet to provide firm evidence as to which aptitudesare the most influential in HCI The absence of defini-tive user models and theories makes challenging the pro-cess of identifying user characteristics significant to VEinteraction Yet while it is easy to say that these lsquolsquoimped-ance matchesrsquorsquo may be task specific we believe that thereare sufficient generalizations possible such that depen-dence on the lsquolsquotask specificrsquorsquo excuse should be avoided atall costs since this comment is so non-informative

In HCI one of the primary user characteristics thatinterface designers adapt to is the level of experience orthe expert-versus-novice paradigm (Dix et al 1993Eberts 1994 Egan 1988) Eberts (1994) noted thatexperts and novices have diverse capabilities and require-ments that may not be compatible Thus computer sys-tems need to be adaptable to these diverse needs Expe-rience level influences the skills of the user the abilitiesthat predict performance and the manner in which usersunderstand and organize task information In examiningthe influences of experience on HVEI one could predictthat experience would influence the skill with which us-ers interact with the VE and the manner in which usersmentally represent a virtual environment over time Suchdifferences could affect the perceived navigational com-plexity of a VE and the benchmark performance of users

Another adaptive approach is to capitalize on the plas-ticity of human cognitive abilities Several HCI studies(Egan amp Gomez 1985 Gomez Egan amp Bowers1986 Vicente Hayes amp Williges 1987 Stanney amp Sal-vendy 1995) have suggested that in general technicalaptitudes (eg spatial visualization orientation spatialmemory spatial scanning) are significant in predictingHCI performance These studies generally focused oninformation search tasks which predictably share charac-teristics with many VE tasks that involve navigation(eg architectural walk-throughs or training groundssuch as battlefields which users must search through) orwhen VEs are used to organize and structure informa-

tion databases The HCI studies indicated that individu-als who score low on spatial memory tests generally havelonger mean execution times and more first-try errorsThese studies also suggest that the difficulties experi-enced by low-spatial individuals were particularly relatedto system navigation issuesmdashusers often report beinglsquolsquolostrsquorsquo within hierarchical menu systems (Sellen et al1990) These findings are particularly relevant to VEsthat often place a high demand on navigation skills Infact VE users are already known to become lost in vir-tual worlds McGovern (1993) found that operators ofteleoperated land vehicles even when using maps andlandmarks have a propensity for becoming lost Thisresult is not surprising since knowledge acquisition frommaps is more challenging for some individuals than forothers and has been found to be associated with highvisualspatial ability (Thorndyke amp Statz 1980)

The issue is thus how to assist low-spatial users withmaintaining spatial orientation within virtual worldsSome insight into this issue was provided by a study thatindicated that although low-spatial individuals are un-able to mentally induce the structure of multidimen-sional complex systems they are capable of recognizingthe structure of systems when they are well organizedand when focus is placed on acquiring their structure(Stanney amp Salvendy 1994) Initial interactions withVEs by low-spatial individuals may thus be best focusedon system structure (ie layout) exploration rather thantask accomplishments until users have recognized thespatial structure of the virtual world (Note A prerequi-site to this suggested approach would be for the VE tobe well organized using a salient structure) If task work-load is high during the initial stages of system use it islikely that low-spatial individuals will have limited abilityto generate an accurate representation of the VE layout(Williams et al 1994)

Predictably anyone who has performed human sub-jects research with VEs will have noted the marked di-versity in usersrsquo abilities to move about and manipulateobjects in a virtual world While some users experienceno difficulties with these tasks others find them non-intuitive and challenging to accomplish It should benoted that these early HVEI findings are referring tolargely visual virtual worlds The problem may com-

Stanney et al 333

pound as we place greater emphasis on audio kines-thetic and haptic interaction modes in virtual environ-ments Thus while motor ability has not been found toconsistently predict human computer performance(Egan 1988) it may become more influential duringHVEI It is therefore essential that human-factors analy-sis be devoted to understanding the influences of variousaptitudes such as motor and verbal abilities on HVEI

Another user characteristic that may influence HVEIis personality Personality traits have generally not beenfound to significantly predict computer performance(Egan 1988) possibly because of the low retest reliabili-ties of most personality tests (Peterson Lane ampKennedy 1965) Nonetheless personality traits maybecome increasingly important during more-complexinteractions such as those experienced in virtual environ-ments Particularly if HVEI is modeled after human-human communication (Eberts 1994) or human-envi-ronment interaction the influences of personality maybecome more influential Methods for improved mea-surement should be developed to facilitate the investiga-tion of these effects

Age is another factor that could affect HVEI Age isinfluential in determining how much difficulty a user willexperience in learning a system (Egan 1988) The morecomplex a system becomes the more influential are theeffects of age particularly if information from differentsensory channels is to be integrated This is disturbingsince it is predictable with their multimodal interactionand complex visual scenes that VEs will oftentimes bemore complex than the systems used in past HCI stud-ies With significant age effects it would thus be benefi-cial to determine how to adapt VEs to the needs of olderindividuals The manner in which age influences com-puter performance however has yet to be fully under-stood

Deficits in perception and cognition which are oftenexperienced by the elderly (Birren amp Livingston 1985Fisk amp Rogers 1991 Hertzog 1989 Salthouse 1992)may lead to a reduction in the information perceivedfrom VE scenes For example diminution of sensoryinput from the eyes experienced by older individuals(Rosenbloom amp Morgan 1986) may impede visual per-ception More specifically older individuals generallyexperience lower visual acuity and reduced contrast sen-

sitivity that could limit sensory input from a virtual envi-ronment This reduction in perception could in turnpresent difficulties to elderly users when navigating vir-tual worlds or manipulating virtual objects It is impor-tant to consider the influences of age on HVEI particu-larly due to the potential this technology has forproviding the elderly who are often isolated from theworld with stimulating interactive activities

There are thus several user characteristics that may berelevant to HVEI These factors need to be identifiedand the level of their influence on HVEI needs to bedetermined

23 VE Design Constraints Relatedto Human Sensory Limitations

In order for designers to be able to maximize hu-man efficiency in VEs it is essential to obtain an under-standing of design constraints imposed by human sen-sory and motor physiology Without a foundation ofknowledge in these areas there is a chance that VE sys-tems will not be compatible with their users VE designrequirements and constraints should thus be developedby taking into consideration the abilities and limitationsof human sensory and motor physiology The physi-ological and perceptual issues that directly impact thedesign of VEs include visual perception auditory per-ception and haptic and kinesthetic perception Each ofthese issues is discussed below

231 Visual perception The design of visualpresentations for VEs is complicated because the humanvisual system is very sensitive to any anomalies in per-ceived imagery (Larijani 1994) The smallest almostimperceptible anomaly becomes dreadfully apparentwhen motion is introduced into a virtual scene becausevisual flow field cues take on an unnatural appearance(Kalawsky 1993) More specifically if a VE is unable togenerate approximate optical flow patterns then theuser becomes very aware that the experience is not natu-ral

For example in VEs used for driver training observ-ers may perceive moving objects during self-motion(eg other traffic while driving) Berthelon and Mestre(1993) have explained driversrsquo perception of moving


vehicles in terms of Gibsonrsquos (1979) optical flow theoryThe implication is that for more-effective visual displaysoptical flow needs to be taken into account when de-signing VE driving simulators as is now being done byLevine and Mourant (1994)

Overall the presentation of motion scenes in VEsneeds further study in order to ensure that the most-effective visual scenes are developed Presently VE sys-tems ordinarily provide the same image to both eyes andthus do not present a lsquolsquorealrsquorsquo stereo image When they doprovide stereo adjustments for the interpupillary dis-tance (IPD) are critical and these adjustments can causeproblems during post-exposure readaptation to norma-tive conditions Also VE systems almost always do notrender binocular movement parallax properties and willnot in the future unless they are tied to accommodation

Another major factor is the viewerrsquos visual field whenwearing a head-mounted display (HMD) There aremany different ways to graphically present the field ofview (FOV) of an individual including polar chartsequal-area projection plots and rectilinear plots (Kalaw-sky 1993) These multiple approaches make it difficultwhen comparing VE systems based on their FOV Fur-ther manufacturersrsquo estimates of FOV are often inaccu-rate (Rinalducci Mapes Cinq-Mars amp Higgins 1996Robinett amp Rolland 1992) Thus researchers must of-ten independently determine the FOV of their devicethrough engineering or optical analyses Rinalducci et al(1996) have recently developed a simple psychophysicalprocedure for determining the FOV for an HMD whichinvolves matching the size of an HMD image to that ofan afterimage having a known angular subtense Withany of these methods it is important to overlay thegraphical dimensions of the observerrsquos visual field ontoobscuration plots HMDs substantially reduce the FOVof a user obscuring the perception of motion in the pe-ripheral vision Current systems are generally limited to aFOV of 707 per eye and do not provide enough periph-eral vision Many VE tasks may require FOVs of 1007 ormore in order to achieve a feeling of immersion As theFOV is expanded however the resolution of the pro-jected images declines (Biocca 1992a) In additionwider FOVs have been implicated in greater sensationsof motion sickness (Pausch Crea amp Conway 1992) Itis thus essential to determine what FOV is required to

perform different kinds of VE tasks effectively Then theextent to which FOVs need to be enlarged can be speci-fied Arthur (1996) is investigating the effects of FOVon human task performance using a representative set ofspatial tasks The results from this study are intended toprovide design guidelines to HMD and VE developersso that an appropriate FOV can be chosen for a givenapplication and task

Another physiological issue in VEs is related to stere-opsis Stereopsis describes the perceptual transformationof differences between the two monocular images seenby the eyes It is a functional component of depth per-ception though and not an essential element for per-ception of depth Stereopsis is important to study be-cause of the emphasis placed on the benefits of depthperception to virtual world performance (Ellis ampBucher 1994 Ellis amp Menges 1995 McDowall 1994)Modern VE systems present problems directly related tothe lack of appropriate stereopsis (Mon-Williams Wannamp Rushton 1993 Rushton Mon-Williams amp Wann1994)

The portion of the visual field shared by both eyes isknown as the binocular field of vision (ie stereopsis)(Haber amp Hershenson 1973) Partial binocular overlapcan be used in VEs to achieve depth perception inwhich a monocular image is displaced inwards or out-wards Such partial overlap can be used to realize wideFOVs with smaller and lighter HMDs In order to haveeffective depth perception in VEs with partial overlaphowever the required degree of overlap must be deter-mined Currently the amount of overlap required is notwell understood Human-factors practitioners need toperform perceptual and human performance studies todetermine if partial overlap is acceptable and what levelsare required for different applications (See Mon-Wil-liams et al 1993 Rushton et al 1994)

Another issue related to stereopsis is binocular rivalry(Kalawsky 1993) When two different images are pre-sented to an observer the image of the dominant eyeoften dominates the visual system Binocular rivalry ef-fects which can be extremely disturbing sensations oc-cur when the dominant image alternates from one eye tothe other Differences in size display scene representa-tion and complexity brightness and hue can all lead tobinocular rivalry effects Such effects are common in

Stanney et al 335

synthetic scenes such as VEs Rivalry is especially presentin augmented (overlaid) reality systems A means ofmoderating or eliminating these disturbing effects isneeded for VEs to receive wide user acceptance

For VE designers trying to achieve stereo depth per-ception it is important to note that lateral image dispar-ity (in the range of 07 to 107) leads to depth perception(Kalawsky 1993) On the other hand vertical imagedisparities do not convey any depth cues In fact smallamounts can lead to double vision (diplopia) Althoughusers can adapt to diplopia in 15 to 20 minutes theymust readjust to visual scenes when they reenter the realworld Such distortion could lead to safety issues De-briefing protocols that instruct users how to proceedafter VE interaction may be needed to assure the safetyof users

It is also important to note that depth perception isdependent on whether a scene is static or dynamic (Rus-sell amp Miles 1993) Depth perception of dynamicscenes such as those in VEs is very complex and notwell understood It is thus important to perform depth-perception studies with both static and dynamic scenessince the results from the former may not generalize tothe later

232 Auditory perception In order to synthe-size a realistic auditory environment it is important toobtain a better understanding of how the ears receivesound particularly focusing on 3-D audio localizationAudio localization assists listeners in distinguishing sepa-rate sound sources Localization is primarily determinedby intensity differences and temporal or phase differ-ences between signals at the ears (Begault amp Wenzel1993 Middlebrooks amp Green 1991) More specificallythe degree to which one sound masks another dependson the relative frequency intensity and location ofsound sources Audio localization is affected by the pres-ence of other sounds and the direction from which thesesounds originate The human ear can locate a soundsource even in the presence of strong conflicting echoesby rejecting the unwanted sounds Biocca (1992a) statesthat lsquolsquothe aural realism of virtual spaces requires replicat-ing the spatial characteristics of sounds like the changingintensity of a race car engine as it screeches pastrsquorsquoThe human ear can also isolate a particular sound source

from among a collection of others all originating fromdifferent locations (Koenig 1950) In order to effec-tively develop aural displays this ability of listeners totrack and focus in on a particular auditory source (iethe cocktail party effect) needs to be better understood

Auditory localization is understood in the horizontalplane (left to right) Sounds can arrive 700 microsecondsearlier to one ear than the other and the sound in thefarther ear can be attenuated by as much as 35 decibelsrelative to the nearer ear (Middlebrooks et al 1991)For example if a listener perceives a sound coming fromthe right generally the sound has arrived to the right earfirst andor is louder in the right ear as compared to theleft When sound sources are beyond one meter fromthe head these interaural time and intensity differencesbecome less pronounced in assisting audio localization

Vertical localization in the median plane cannot de-pend on interaural differences (ie as long as the headand ear are symmetrical) When a sound is directly infront of (or behind) a listener the interaural differencesare zero however the listener is still somehow able tolocalize the sound In such cases the anatomy of theexternal ear (ie the pinna) is thought to producechanges in the spectrum of a sound (ie spectral shapecues) that assist in localizing the sound (Fisher amp Freed-man 1968 Middlebrooks et al 1991)

Thus in order to effectively characterize 3-D audiolocalization binaural localization cues received by theears can be represented by the pinna cues as well as byinteraural acoustical differences Recently a Head Re-lated Transfer Function (HRTF) has been used to repre-sent the manner in which sound sources change as a lis-tener moves hisher head and can be specified withknowledge of the source position and the position andorientation of the head (Butler 1987 Cohen 1992)The HRTF is dependent on the physiological makeup ofthe listenerrsquos ear (ie the pinna does a nonlinear fittingjob in the HRTF) Recent advances have allowed for thedevelopment of personalized HRTFs (Crystal RiversEngineering 1995) These personalized functions stillrequire a significant amount of calibration time Ideallya more-generalized HRTF could be developed thatwould be applicable to a multitude of users This may bepossible since the transfer functions of the external earhave been found to be similar across different individu-


als although there tends to be a downward shift in spec-tra frequency with increasing physical size (Middle-brooks Makous amp Green 1989)

233 Physiology of haptic and kinestheticperception A haptic sensation (ie touch) is a me-chanical contact with the skin It is important to incor-porate haptic feedback in VEs because such feedback hasbeen found to substantially enhance performance (Bur-dea et al 1994) For example by incorporating hapticfeedback into synthetic molecular modeling systems theproblem-solving ability of chemists was significantly en-hanced (Brooks Ouh-Young Batter amp Kilpatrick 1990Minsky Ouh-Young Steele Brooks amp Behensky 1990)

Three mechanical stimuli produce the sensation oftouch a displacement of the skin over an extended pe-riod of time a transitory (a few milliseconds) displace-ment of the skin and a transitory displacement of theskin that is repeated at a constant or variable frequency(Geldard 1972) Even with the understanding of theseglobal mechanisms however the attributes of the skinare difficult to characterize in a quantitative fashion Thisis due to the fact that the skin has variable thresholds fortouch (vibrotactile thresholds) and can perform complexspatial and temporal summations that are all a functionof the type and position of the mechanical stimuli (Hill1967) So as the stimulus changes so does the sensationof touch thus creating a challenge for those attemptingto model synthetic haptic feedback

Another haptic issue is that the sensations of the skinadapt with exposure to a stimuli More specifically the effectof a sensation decreases in sensitivity to a continued stimulusmay disappear completely even though the stimulus is stillpresent and varies by receptor type Phasic receptors areones that rapidly adapt and relate to pressure touch andsmell Tonic receptors which are related to pain and bodyposition slowly adapt and may have an afterimage that per-sists even once the stimulus is removed

Surface characteristics of the stimulus also influencethe sensation of touch For a hard surface to be felt afterinitial contact active pressure must be maintained Thesensation of textured surfaces requires some relative mo-tion between the surface and the skin to be maintainedSoft surfaces can exert and maintain a slight positive re-action against the skin after the initial contact without

active pressure or relative motion Most current systemsprovide limited haptic feedback generally isolated to thehand For example electrotactile and vibrotactile deviceshave been developed to simulate the sensation of textureand other surface illusions on the hand (KaczmarekWebster Bach-y-Rita amp Thompkins 1991) More fullyhaptic feedback may be needed to enhance performanceand presence (Biocca 1992a) Current exoskeletons arecumbersome and expensive A less-invasive means ofproviding full haptic feedback is desirable

In order to communicate the sensation of syntheticremote touch it is thus essential to have an understand-ing of the mechanical stimuli which produce the sensa-tion of touch the vibrotactile thresholds the effect of asensation the dynamic range of the touch receptors andthe adaptation of these receptors to certain types ofstimuli The human haptic system thus needs to be morefully characterized potentially through a computationalmodel of the physical properties of the skin in order togenerate synthesized haptic responses

Kinesthesia is an awareness of the movements andrelative position of body parts and is determined by therate and direction of movement of the limbs the staticposition of the limbs when movement is absent tensionsignals originating from sensory receptors in the jointsskin and muscles and visual cues (Kalawsky 1993)Kinesthetic issues for VE design include the facts that asmall rate of movement of a joint can be too small forperception that certain kinesthetic effects are not wellunderstood (eg tensing the muscles improves move-ment sense) and that humans possess an internal mentalimage of the positions of limbsjoints that is not depen-dent on actual sensing information There is thus a greatdeal to be learned about how to integrate the capacitiesof the human into the design of a VE

24 Integration Issues withMultimodal Interaction

While developers are focusing on synthesizing ef-fective visual auditory and haptic representations invirtual worlds it is also important to determine how toeffectively integrate this multimodal interaction One ofthe aspects that makes VEs unique from other interactive

Stanney et al 337

technologies is their ability to present the user with mul-tiple inputs and outputs This multimodal interactionmay be a primary factor that leads to enhanced humanperformance for certain tasks presented in virtual worldsEarly studies have already indicated that sensorial redun-dancy such as visual auditory and tactical feedback(Fukui amp Shimojo 1992) can enhance human perfor-mance in virtual worlds One demonstration of the ben-efits of such multimodal user feedback was provided byMassimino and Sheridan (1994) who found enhancedperformance with visual and force feedback as com-pared to no force feedback in a peg-in-hole task Thereis currently however a limited understanding on how toeffectively provide such sensorial parallelism (Burdea etal 1994) When sensorial redundancy is provided tousers it is essential to consider the design of the integra-tion of these multiple sources of feedback One means ofaddressing this integration issue is to consider the coor-dination between sensing and user command and thetransposition of senses in the feedback loop

Command coordination considers the user input asprimarily monomodal (eg through gesture or voice)and feedback to the user as multimodal (ie any combi-nation of auditory visual andor haptic) There is lim-ited understanding on such issues as

(1) Is there any need for redundant user input (egvoice and direct manipulation used to activate thesame action)

(2) Can users effectively handle parallel input (egselect an object with a dataglove at the same timeas directing a search via voice input)

(3) For which tasks is voice input most appropriategesture most appropriate and direct manipulationmost appropriate

The use of redundant user inputs may seem unnecessaryConsider however a designer who is modeling hu-man-VE interaction based on human-human communi-cation a recognized approach to human-computer in-terface design (Eberts 1994) Redundant lsquoinputsrsquo areoften used in human-human communication such asduring a greeting where individuals simultaneously ex-change verbal salutations and handshakes In this case averbal input is combined with a gesture for effectivecommunication Such redundant inputs could poten-

tially be useful in HVEI Redundant input capabilitycould also support user preferences (ie some users mayprefer verbal interaction while others may favor directmanipulation) When providing redundant feedback itwill be essential to consider the limitations of human-information processing (Card et al 1983) to avoid sen-sorial overload VE designers thus need to establish themost-effective command coordination schemes for theirVE tasks

Sensorial transposition occurs when a user receivesfeedback through other senses than those expected Thismay occur because a VE designerrsquos command coordina-tion scheme has substituted unavailable system sensoryfeedback (eg force feedback) with other modes offeedback (eg visual or auditory) Such substitution hasbeen found to be feasible (eg Massimino amp Sheridan1993 successfully substituted vibrotactile and auditoryfeedback for force feedback in a peg-in-hole task)

The sensorial substitution schemes may be one-for-one (eg sound for force visual for force visual forsound) or more complex (eg visual for force and audi-tory visual and auditory for force) (Burdea amp Coiffet1994) VE designers thus need to establish the most-effective sensorial transposition schemes for their VEtasks The design of these substitutions schemes shouldbe consistent throughout the virtual world to avoid sen-sorial confusion

25 Virtual EnvironmentDesign Metaphors

It is known that well-designed metaphors can assistnovice users in effectively performing tasks in human-computer interaction (Carroll amp Mack 1985) Design-ing effective VE metaphors could similarly enhance hu-man performance in virtual worlds Such metaphors mayalso be a means of assisting in the integration of multi-modal interaction For example affordances may be de-signed that assist users in interacting with the virtualworld much as they would interact with the multimodalreal world Affordances are the goals naturally furnishedby an environment (Shaw Kugler amp Kinsella-Shaw1990) They are the environmental properties that caus-ally support goal-directed behavior To be effective in


managing human performance VE affordance proper-ties need to be represented by both an inflow of control-lable human behavior and an outflow of detectable in-formation (ie optic haptic olfactory flow pattern)Reactions to this information could then feed back intothe cycle and direct the inflow of additional controlledhuman behavior In this manner environmental cues in avirtual world could elicit and direct the behavior of us-ers Well-designed affordances could reduce the per-ceived navigational complexity of a VE and enhance us-ersrsquo benchmark task performance Unfortunately at thepresent time many human-VE interface designers areusing old affordances and metaphors (eg windowstoolbars) that may be inappropriate for HVEI

Oren (1990) suggested that every new technologygoes through an initial incunabular stage where oldforms continue to exist that may not be uniquely suitedto the new medium Virtual environments are in need ofnew design metaphors uniquely suited to their character-istics and requirements McDowall (1994) has suggestedthat the design of interface metaphors may prove to bethe most challenging area in VE development VR slid-ers (3-D equivalents of scroll bars) map cubes (3-Dmaps that show space in a viewerrsquos vicinity) and towplanes (where a viewerrsquos navigation is tied to a virtualobject that tows himher about the VE) are all beinginvestigated as potential visual metaphors for VEs Por-tals and spirals are being investigated as potential re-placements for windows (Laurel 1994)

Beyond the need for new visual metaphors VEs mayalso need auditory metaphors that provide a means ofeffectively presenting auditory information to users Co-hen (1992) has provided some insight into potentialauditory metaphors through the development of lsquolsquomulti-dimensional audio windowsrsquorsquo or MAWs MAWs providea conceptual model for organizing and controllingsound within traditional window-icon-menu-pointingdevice (WIMP) interfaces Metaphors for haptic interac-tion may also be required Limited work has been donein this area to date and no noted haptic metaphors havebeen presented

VE designers have in the past been guided by thedesign objects available in most 2-D toolkits (ie win-dows icons menus pointing devices) Existing HCI

guidelines are generally structured around the use ofsuch toolkits (Dix et al 1993) VE designers are nothowever bound by the limitations of such toolkits theyare rather bound by their creativity and design profi-ciency With this freedom from toolkits however comesthe loss of the associated guidance these constraints pro-vide Although VE designers will have virtually endlessdesign possibilities they also currently have limitedguidance in designing effective human-virtual environ-ment interfaces Research into the design of new VEmetaphorsmdashand more importantly guidelines to de-velop such metaphorsmdashis needed Current HCI guide-lines focus primarily on the visual metaphor For ex-ample Shneiderman (1992) provides design guidelinesfor data display and data entry both primarily visuallydriven VE design guidelines however will need to bemultisensory providing guidance for the design of vi-sual auditory and kinesthetic information The key tothe design of these new metaphors may be to identifyexpectations developed through real-world experiencesin common and familiar environments and to use thisknowledge to design consistent VE interaction meta-phors (Ellis 1993) This approach is an extension of theanthropomorphic approach that uses models of human-human communication to direct the design of human-computer interaction (Eberts 1994) Using this ap-proach the constancies expectations and constraintselicited from interactions in the real world should bedesigned into VE metaphors thereby potentially engen-dering a more intuitive interface design

3 Health and Safety Issues inVirtual Environments

Maximizing human performance in VEs is essentialto the success of this technology Of equal importance isensuring the health and welfare of users who interactwith these environments (See Figure 1) If the humanelement in these systems is ignored or minimized itcould result in discomfort harm or even injury It isessential that VE developers ensure that advances in VEtechnology do not come at the expense of human well-being

Stanney et al 339

There are several health and safety issues that may af-fect users of VEs These issues include both direct andindirect effects The direct effects can be looked at froma microscopic level (eg individual tissue) or a macro-scopic level (eg trauma sickness) The indirect effectsinclude physiological aftereffects and psychological dis-turbances

31 Direct Microscopic Effects

There are several microscopic direct effects thatcould affect the tissues of VE users The eyes which willbe closely coupled to HMDs or other visual displaysused in VEs have the potential of being harmed Theeyes may be affected by the electromagnetic field (emf)of VEs if the exposure is sufficiently intense or pro-longed (Viirre 1994) Emf exposure could cause cata-racts if the CRT used produces X-rays Laser lights arealso being considered for use in HMD and movement-detection systems Standards exist for laser exposure thatshould be reviewed and adhered to by VE developers tominimize harm In addition eyestrain could be causedby poor adjustment of HMD displays as well as flickerglare and other visual distortions (Ebenholtz 19881992 Konz 1983 Sanders amp McCormick 1993)Mon-Williams Wann and Rushton (1993) found thatafter subjects wore a binocular HMD with an IPD fixedto the mean of the subject group for ten minutes theyexperienced a significant shift in vergence bias towardsesophoria (inward turning of the eyes) during distancevision A later study (Rushton et al 1994) using thesame procedure but a different biocular HMD (ratherthan the earlier binocular HMD that generated conflictsbetween depth cues presented by image disparity andimage focal depth) found no significant problems forexposure durations of up to 30 minutes These resultsindicate that through careful HMD design prismaticeffects associated with incorrect IPD settings poor illu-mination poor contrast and the close proximity of theworking distance can be minimized If not consideredhowever these results indicate that significant visualstress from HMD exposure can occur and lead to ocularsymptoms (eg unstable binocular vision and reducedvisual acuity) Related visual aftereffects may engender

an individual unsafe to interact with the real world (egdrive a car or ride a skateboard) after VE exposure

There is concern over emf exposure (Viirre 1994) Itmay be that mild emf exposure is harmless but this hasyet to be proven Strong emfs could on the other handcause cellular and genetic material damage in the brainas in other tissues The issue is that at present we do nothave a solid understanding of the effects of longtermemf exposure

Phobic effects may result from VE use such as claus-trophobia (eg HMD enclosure) and anxiety (eg fall-ing off a cliff in a virtual world) Viirre (1994) suggestsbut has yet to prove that no longterm phobic effectsshould result from HVEI except potential avoidance ofVE exposure

The auditory system and inner ear could be adverselyeffected by VE exposure to high volume audio (eg thelsquolsquoWalkmanrsquorsquo effect) One of the possible effects of suchexposure is noise-induced hearing loss Continuous ex-posure to high noise levels (particularly above 80 dBA)can lead to nerve deafness (Sanders amp McCormick1993) The Occupational Safety and Health Administra-tion (OSHA) has noise exposure limits that should befollowed for VE design in order to prevent such hearingloss (OSHA 1983)

Prolonged repetitive VE movements could also causeoveruse injuries to the body (eg carpal tunnel syn-drome tenosynovitis epicondylitis) The propensity forusers to be inflicted by such ailments can be moderatedby emphasizing ergonomics in VE design and judicioususage procedures

The head neck and spine could be harmed by theweight or position of HMDs DiZio and Lackner (1992)have observed that users who move about with HMDsweighing 25 pounds or more experience an increase inthe inertia of head movements that could easily lead tomovement injuries In addition this additional headweight often leads to symptoms of motion sickness

32 Direct Macroscopic Effects

The risk of physical injury or trauma from VE in-teraction is of real concern VE equipment is complexand interferes with normal sensory perception and bodymovements Limited or eliminated vision of natural sur-


roundings when wearing HMDs could lead to falls ortrips that result in bumps and bruises Sound cues maydistract users causing them to fall while viewing virtualscenes Imbalance of body position may occur due to theweight of VE equipment or tethers that link equipmentto computers causing users to fall (Thomas amp Stuart1992) Such tethers may not be visible in the virtualworld and thus could pose a threat to the safety of usersIf haptic feedback systems fail a user might be acciden-tally pinched pulled or otherwise harmed Most force-feedback systems attenuate the transmitted force toavoid harm (Biocca 1992a) As previously discussedanother direct macroscopic effect is that users may be-come motion sick (ie cybersickness) or potentially ex-perience maladaptive physiological aftereffects from hu-man-virtual environment interaction

321 Cybersickness One of the most importanthealth and safety issues that may influence the advance-ment of VE technology is cybersickness Cybersickness isa form of motion sickness that occurs as a result of expo-sure to VEs Cybersickness poses a serious threat to theusability of VR systems Users of VE systems may experi-ence various levels of sickness ranging from a slightheadache to an emetic response Although there aremany suggestions about the causes of cybersickness todate there are no definitive predictive theories althoughthere are models in general Research needs to be donein order to identify the specific causes of cybersicknessand their interrelationships in order to develop methodsthat alleviate this malady Without such an understand-ing cybersickness may remain a lsquolsquosnakersquorsquo lingering in theunderbrush of VE use and threatening the widespreaddiffusion of this technology (Biocca 1992b)

There have been several factors identified that maycontribute to cybersickness (eg vection lag field ofview) Vection a factor often associated with motionsickness is the illusion of self-movement in a VE whenthe body senses that there is no actual physical move-ment a conflict occurs between the visual and vestibularsystems which is believed to lead to sickness (HettingerBerbaum Kennedy Dunlap amp Nolan 1990) It hasbeen suggested that this cue conflict can be resolved byadding a motion base to simulators In a study con-

ducted on helicopter pilots using both motion-base andfixed-base simulators however both groups of pilotsbecame equally sick (McCauley amp Sharkey 1992)

In virtual systems lag occurs when a user perceives adelay between the time a physical motion is made (egturning the head to the right) and the time the com-puter responds with a corresponding change in the dis-play Such transport delays (ie lags) and asynchronybetween two different inputs (eg visual and inertial)are often indicted in connection with cybersickness butthe data are sparse Several have speculated that thesedistortions are the temporal analogies of spatial distor-tions and rearrangements that make people sick usingmirrors and prisms (Kennedy Lilienthal BerbaumDunlap Mulligan amp Funaro 1987) The best evidenceis that Navy simulators with the longest transport delayshave the highest sickness rates It has been hypothesizedthat asynchrony may be more provocative of sicknessthan lags User adaptation to the VE should be rapid ifthe lags are constant or not at all if they are variable

Both wide and narrow fields of view have been sug-gested to lead to motion sickness Lestienne Soechtingand Berthoz (1977) found that subjects who viewed awide field of view (FOV) experienced intense sensationsof motion sickness Nausea has also been found to occurhowever when the field of view is restricted (Andersonamp Braunstein 1985) Such experiments suggest thatfield of view may not be an overriding indicator ofwhether or not cybersickness is experienced HowardOhmi Simpson and Landolt (1987) found that what isperceived as being in the distance drives vection which inturn often drives sickness Since the peripheral FOV usu-ally has been the main factor investigated for its effectson vection perhaps depth per se needs to be studied asthe vection and sickness driver

The noted contradictory evidence among these mo-tion sickness studies leads to skepticism about the actualimpact of each of these factors With the lack of defini-tive predictive theories other potential solutions mustbe pursued Mental rotation exercises have been cited asa means of identifying individuals who should be lesssusceptible to motion sickness and for potentially train-ing others to improve their mental rotation capabilitiesthereby moderating sickness (Parker amp Harm 1992)This approach may work as a screening device however

Stanney et al 341

based on studies of spatial orientation ability (Witkin1950) it is unlikely that those individuals low in spatialability will acquire the capability to resolve inconsisten-cies in the relationships between virtual scene polarityand their internal body axes simply through mental rota-tion exercises The reliability of tests that measure men-tal rotation ability (eg Ekstrom French amp Harman1976) indicates that this aptitude is probably not readilylearned but rather an innate ability which each indi-vidual possesses to some degree

One promising approach to moderating cybersicknessis through the manipulation of the level of interactivecontrol provided to users Control may provide userswith a means of adapting to or accommodating cue con-flicts by building conditioned expectations through re-peated interactions with a virtual world (eg when auserrsquos head turns the user learns to expect the world tofollow milliseconds behind) Lack of control would notallow such expectations to be established since userswould not be aware of which way they were turning atany particular moment (ie the course would be deter-mined by the system)

Freedom of movement or control and its effect oncybersickness has not been adequately researched Somestudies imply that control may be a major factor influ-encing sickness Reason and Diaz (1971) and Casali andWierwille (1986) determined that crewmembers andcopilots are more susceptible to sickness because theyhave little or no control over the simulators movementsLackner (1990) suggested that the lsquolsquodriverrsquorsquo of a simula-tor becomes less sick than passengers because heshecan control or anticipate the motion McCauley andSharkey (1992) suggest that at lsquolsquohigh altitudes andor atlower speedsrsquorsquo freedom of movement will minimize cy-bersickness Krueger (1991) has suggested that cyber-sickness may be modified by having individuals alternatebetween control and no-control situations There issome empirical evidence to support the use of control asa moderator of cybersickness in virtual environmentsStanney and Hash (in press) conducted a VE study inwhich three levels of user-initiated control were exam-ined (no control complete control and coupled con-trol) The results indicated that the coupled control con-dition (ie in which the degrees of freedom of motion

were matched to the needs of the task) produced signifi-cantly less sickness than the no-control and complete-control conditions

Further study is needed to determine the exact natureof the relationship between control and cybersicknessThe attractiveness of such a control theory if proven isthat the level of user-initiated control could potentiallybe manipulated in order to alleviate the influences ofother factors such as vection and lag in order to moder-ate sickness Control also needs to be tested against vary-ing degrees of other factors to see what level of freedomis necessary to potentially negate their effects The re-search should focus on developing a general theory ofcybersickness that would allow for the prediction of thecombinations of factors that would be disruptive andlead to sickness those that would be easy or hard toadapt to and the relationship of these levels of adapta-tion to the level of user control Such a theory wouldprovide VE developers with the knowledge necessary tominimize the adverse effects of human-virtual environ-ment interaction

33 Indirect Effects

While cybersickness is a commonly cited concernof HVEI a less-known yet equally or even more impor-tant indirect consequence of HVEI is the potential del-eterious physiological aftereffects from VE exposureThe use of VEs may produce disturbing aftereffectssuch as head spinning postural ataxia reduced eye-handcoordination vestibular disturbances andor sicknessThe plasticity of the human nervous system allows someindividuals to adapt becoming less ill with continuedsystem interaction (Dolezal 1982 Guedry 1965Welch 1978) This adaptation is characterized by a de-cline in the initial response to an altered stimulus devel-opment of an altered often compensatory response fol-lowing prolonged exposure to the change and acontinuation of the adapted response (ie an aftereffect)once the stimulus is removed (Parker amp Parker 1990)Such aftereffects have been known to persist for severalhours after system exposure (Baltzley Kennedy Ber-baum Lilienthal amp Gower 1989 Crosby amp Kennedy1982 Ungs 1987) Individuals who tend to remain sick


and experience continued discomfort during VE interac-tion may actually have an advantage when returning tothe normative conditions to which they remain physi-ologically suited

Thus while adaptation sounds advantageous becauseadaptive individuals become less ill with repeated expo-sure the physiological modifications that elicit this adap-tation are of concern These physiological aftereffectsmay make individuals maladapted (ie at risk of injury)for the return to the real world once VE interaction con-cludes Some of the most disturbing aftereffects includeflashbacks illusory climbing and turning sensations per-ceived inversions of the visual field reduced motor con-trol (Kennedy Lane Lilienthal Berbaum amp Hettinger1992 Rolland Biocca Barlow amp Kancherla 1995)reduced complex psychomotor flexibility (Lampton etal 1994) a disturbed vestibulo-ocular reflex (VOR)function (Hettinger Berbaum Kennedy amp Westra1987) postural disturbances (Kennedy Fowlkes amp Lil-ienthal 1993) and increased risk of adverse adaptationsto subsequent normal environments (Regan 1993)

The implication is that with protracted or repeatedexposures those individuals who exit VE interactionsfeeling less affected (ie less ill) may actually be the onesat greatest risk This was seen in studies of postural sta-bility where subjectsrsquo reports of motion sickness pro-gressively diminished upon exiting over continued sys-tem interaction while objectively measured ataxiaworsened (Kennedy Lanham Drexler amp Lilienthal1995) Such aftereffects led the Navy and Marine Corpsto institute grounding policies after simulator flightsseveral years ago (Kennedy Lilienthal Berbaum Baltz-ley amp McCauley 1989) Similar bans on driving roofrepair or other machinery use after VE exposure may benecessary Delayed effects from virtual experiencesshould also be investigated in order to ensure the safetyof users once interaction with a virtual world concludes

The existence of these aftereffects indicates that theprimary approach to measuring the deleterious effects ofVE interaction ie subjective reports of motion sicknessafter VE exposure may provide little indication of thereduction in physiological functioning actually experi-enced by individuals For this reason more physiologi-cally based tests are needed to objectively measure the

aftereffects of VE exposure and to ensure the safety ofusers Tests of postural stability have already been devel-oped (Kennedy amp Stanney 1996) This measure can beemployed before and after exposure to a VE system tocertify that a userrsquos balance upon exiting the system is atleast demonstrably as good as it was upon entering Cur-rent research is investigating the development of sensori-motor transformation (ie hand-eye coordination) testsof pointing errors induced by exposure to sensory con-flicts in virtual environments (Kennedy Stanney Dun-lap amp Jones 1996)

Much as human-computer interactions were initiallylabeled lsquolsquonon-user friendlyrsquorsquo if negative VE incidentsoccur the technology could be branded lsquolsquounsafersquorsquo andfuture use and proliferation of the technology could behampered The VE technology community should col-laboratively establish health and safety standards that candirect and guide future developments Creating and ad-hering to industry-wide health and safety standardsshould reduce harm to users as well as minimize poten-tial liability risks of developers

4 The Social Impact of Virtual Technology

While researchers are often concerned about hu-man performance and health and safety issues when de-veloping a new technology an often-neglected indirecteffect of new technologies is their potential social im-pact (See Figure 1) Virtual reality is a technologywhich like its ancestors (eg television computersvideo games and simulation) has the potential for nega-tive social implications through misuse and abuse (Kall-man 1993) There is already a high level of concernover the negative influences of television and videogames which are much less interactive environmentsthan VEs Yet violence in VEs is nearly inevitable oneneed only look at the violence in popular video gamesRather than waiting for these issues to arise in VEs itmight be prudent to address social issues before theyresult in crisis or harm

Currently the potential negative social influences re-sulting from VE exposure are not well understood Forexample VE applications that are presented as benign

Stanney et al 343

forms of entertainment but which actually represent vio-lence and destruction may become available at videogame rooms in the near future Such animated violenceis already a known favorite over the portrayal of morebenign emotions such as cooperation friendship or love(Sheridan 1993) The concern is that users who engagein what seems like harmless violence in the virtual worldmay become desensitized to their violent virtual actionsand then mimic that behavior in the look-alike realworld There is concern that virtual interactions couldengender addiction and subtly condition violence

There are many open issues (Stone 1993 Whiteback1993) such as What will be the psychological and char-acter effects of VE use How will interaction in the vir-tual world modify behavior What will the lsquolsquotransfer oftrainingrsquorsquo be for violent virtual interactions Will indi-viduals transfer violent virtual experiences to the realworld Will people turn their backs on the real worldand become contented zombies wandering around syn-thetic worlds that fulfill their whims Will VR users expe-rience traumatic physical or psychological consequencesdue to a virtual interaction Will people avoid reality andreal social encounters with peers and become addicted toescapism Is continual exposure to violent virtual worldssimilar to military training which through continuedexposure may desensitize individuals to the acts of killingand maiming How will VE influence young childrenwho are particularly liable to psychological and moralinfluence Does VE raise issues that are genuinely novelover past media due to the salience of the experience andthe active interaction of the user

Even with all of these concerns there is currently lim-ited focus on the social implications of VE technologyfrom its developers (Kallman 1993) There are strongscientific reasons however why the active engagementavailable in VE games rather than the passive action oftelevision watching can have better retention of learnedskills For example Brunner (1966) demonstrated thatlearning-rich environments facilitate learning by embed-ding learners into a given environment (ie immersion)and allowing them to learn kinesthetically (ie actively)first This learning-by-doing facilitates higher-level cog-nition and retention of the learned skills The implica-tion is that the continual act of virtual violence will facili-

tate a youthrsquos ability to reason and think in the realm ofviolent behavior For these same reasons we should beconcerned about the impact playing these games mayhave on the behavior of youth To the extent that gamessimilar to military combat are employed for recreationalusage then we may breed youth with social problems ofsome magnitude ready willing and able to commit vio-lent acts That the games are exciting involving stressfrom immediate threats the games may teach hasty im-pulsive response rather than thoughtful considerationthat is often needed to avoid violence by seeking alterna-tives

Currently we do not know whether such violent be-havior will result from VR gaming While little system-atic research has been performed in this area the earlydata are not encouraging In a recent study HVEI wasshown to significantly increase the physiological arousaland aggressive thoughts of young adults (Calvert amp Tan1994) The study examined three theories

(1) the arousal theory which states that physiologicalresponses (eg blood pressure heart rate) to ag-gression should initially increase as users engagein a threatening experience which can be chan-neled into aggressive activities similar to thosethat users are exposed to

(2) the social cognitive theory which states that auser can become more aggressive after observingand then imitating aggressive actsmdashafter enoughexposure controls created to inhibit aggressiveactions have become disinhibited or weakened

(3) the psychoanalytic theory which states that a userwill experience a subsequent decrease in aggres-sion through catharsis as one releases aggressivedrives safely in virtual rather than actual experi-ences

The results of the study did not wholly support anyone theory The physiological arousal (ie heart rate)was a function of HVEI however hostile feelings didnot increase as would be predicted by the arousal theoryAggressive thoughts increased as a function of HVEIhowever a passive observational condition did not pro-duce more aggression as would be predicted by the so-cial cognitive theory Unfortunately neither aggressive


thoughts nor hostile feelings decreased from baselinedue to HVEI as would be predicted by the psychoana-lytic theory thus providing no support for catharsis

The results indicate that physiological arousal and ag-gressive thought content may be significant predictors ofHVEI This increased negative stimulation may then bechanneled into other activities in the real world Theconcern is that VR immersion may potentially be amore-powerful perceptual experience than past less-interactive technologies thereby increasing the negativesocial impact of violent interactive technologies

Research needs to be directed at developing a newconceptual model of the social implications of HVEIpotentially one that integrates the supported compo-nents of the arousal and social cognitive theoriesThrough such a model the social consequences ofHVEI may be predicted There are problems with pur-suing this research including the lack of measures toquantify violent behavior the considerable time neededto establish cause-effect relationships and the difficultyof demonstrating a casual link outside of a laboratorysetting We have experienced difficulty in scientificallydetermining whether major factors such as poverty arecauses of violent crime it should prove no less of a chal-lenge for VR technology Worse yet it could take a con-siderable amount of time to establish if there are anynegative social implications from HVEI Consider ciga-rette smoking which was not linked to lung cancer orheart disease until after a generation of Americans haddied in increasing numbers from these diseases As formeasures while indirect measures such as those used byCalvert and Tan (1994) are available a direct assessmentof behavior changes with violent VR gaming is neededbut will predictably not become available very soon

The concern is that violent VR gaming represents anunknown risk of increased violence in the next genera-tion of our youth A proactive approach is needed thatweighs the risks and potential consequences associatedwith VE against the benefits For example the develop-ment of a VE system may improve the lives of severalindividuals (eg toy manufacturers stockholders) yetharm others (eg children who become emotionallyunhealthy due to excessive exposure to violent VRgames) Waiting for the onset of harmful consequences

should not be tolerated Through a careful analysissome of the problems of VEs may be anticipated andperhaps prevented A proactive rather than reactive ap-proach may allow researchers to identify and addresspotentially harmful side-effects related to the use of VEtechnology

5 Conclusions

Computer speed and functionality image process-ing synthetic sound and tracking mechanism have beenjoined together to provide realistic virtual worlds Vir-tual reality is more than a sum of these componentshowever it is inherently a system technology with anessential element being the user of the system While thetechnology still needs perfecting for VEs to be success-ful a fundamental advance requiring immediate attentionis to determine how to effectively design the human-VEinterface The needs and abilities of VE users have notyet been adequately addressed in the design of virtualworlds Since VE real-world applications are growing ata rapid rate human-factors practitioners need to becomeinvolved before improper designs and practices becomecommonplace This paper has structured human-factorsresearch challenges into three primary areas within vir-tual environments human performance efficiencyhealth and safety concerns and social implications Hu-man-factors practitioners must take the lead in resolvingthese challenges to ensure that VE technology developswith adequate concern for its users

While certainly not comprehensive the extent of thispaper is an indication of the number of variables thatneed to be considered when studying human factors is-sues in virtual environments The level of human-factorseffort needed to resolve these issues cannot be ad-equately addressed using traditional analysis techniques(ie selecting a few variables and performing an analysisusing a completely randomized design) The issues withthis approach include the fact that researchers have lim-ited knowledge a priori of which variables are the mostinfluential and it would take a considerable amount oftime to address all treatments in this manner Instead webelieve that researchers should consider using fractional

Stanney et al 345

factorial designs (See Jones amp Kennedy in preparation)These designs permit the introduction of several vari-ables at once with relatively modest sample sizes(n gt 30) in order to first screen lower-order effects (iemain effects and two-way interactions) while recogniz-ing the confounding that occurs with higher-orderterms While the results of such experiments must becarefully interpreted they provide an economic means ofidentifying the variables that have the greatest effect andthat can subsequently be studied in more detail

The HVEI field definitely requires that we be cross-disciplinary The development of VE applications typi-cally involves a team of professionals consisting of graph-ics designers to build 3-D models sound specialists tocreate spatial audio effects mechanical electrical andoptical engineers to design and build interfaces for hu-man-computer interaction (eg data gloves exoskel-etons) and computer programmers and scientists towrite the code to control the complex simulations Westrongly recommend that human-factors personnel be-come part of the development team and evaluate virtualenvironments in terms of their use with human subjectsSuch testing is very important in that there are and willcontinue to be large differences in VEs and VEs will beused by many diverse populations

As computers become more powerful as display tech-nologies permit the viewing of higher-quality imageswith greater FOVs as techniques to experience hapticand force feedback become less costly and as the cre-ation of code to run and manage virtual environments issimplified the use of virtual environments will expand ata rapid rate Since these VEs will involve the interactionof people and machines we need to apply human-factorsprinciples to their design and use

Acknowledgments

The authors wish to thank Phillip Hash for his inputs concern-ing cybersickness and Guillermo Navarro for his inputs con-cerning design metaphors This material is based in part uponwork supported by the National Science Foundation underGrant No IRI-9624968 Any opinions findings and conclu-sions or recommendations expressed in this material are those

of the authors and do not necessarily reflect the views of theNational Science Foundation This work was supported in partby AISP Grant No 10-07-050 University of Central Florida

References

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Adler H E (Ed) (1971) Orientation Sensory basis Annals ofthe New York Academy of Science (p 188)

Adolfson J amp Berghage T (1974) Perception and perfor-mance under water New York Wiley

Anderson G J amp Braunstein M L (1985) Induced self-motion in central vision Journal of Experimental Psychology11 122ndash132

Arthur K (1996) Effects of field of view on task performancewith head mounted displays CHI rsquo96 Proceedings on Hu-man Factors and Computing Systems NY ACM

Baltzley B A Kennedy R S Berbaum K S Lilienthal

M G amp Gower D W (1989) The time course of post-flight simulator sickness symptoms Aviation Space andEnvironmental Medicine 60(11) 1043ndash1048

Barfield W amp Weghorst S (1993) The sense of presencewithin virtual environments a conceptual model In G Salv-endy and M Smith (Eds) Human-computer interactionSoftware and hardware interfaces (pp 699ndash704) Amster-dam Netherlands Elsevier Science Publishers

Begault D R amp Wenzel E M (1993) Headphone localiza-

tion of speech Human Factors 35(2) 361ndash376Berthelon C amp Mestre D (1993) Curvilinear approach to

an intersection and visual detection of a collision HumanFactors 35(3) 521ndash534

Biocca F (1992a) Virtual reality technology A tutorial Jour-nal of Communication 42(4) 23ndash72

Biocca F (1992b) Will simulation sickness slow down thediffusion of virtual environment technology Presence

Teleoperators and Virtual Environments 1(3) 334ndash343Birren J E amp Livingston J (1985) Cognition stress and

aging Englewood Cliffs NJ Prentice HallBrooks F Ouh-Young M Batter J amp Kilpatrick P (1990)

Project GROPEmdashHaptic displays for scientific visualizationProceedings of ACM SIGGRAPH rsquo90 Computer Graphics24(3) 177ndash185


Brunner J (1966) Towards a theory of instruction New YorkW W Norton and Company

Burdea G amp Coiffet P (1994) Virtual reality technology

New York WileyButler R A (1987) An analysis of the monaural displacement

of sound in space Perception amp Psychophysics 41 1ndash7Calvert S L amp Tan S L (1994) Impact of virtual reality on

young adultrsquos physiological arousal and aggressive thoughtsInteraction versus observation Journal of Applied Develop-mental Psychology 15 125ndash139

Card S K Moran T P amp Newell A (1983) The psychologyof the human-computer interaction Hillsdale NJ Lawrence

Erlbaum AssociatesCarroll J M amp Mack R L (1985) Metaphor computing

systems and active learning International Journal of Man-Machine Studies 22 39ndash57

Casali J G amp Wierwille W (1986) Vehicular simulator-in-duced sickness (Report No NTSC-TR86-012 (AD-A173226) Vol 3) (p 155) Arlington VA Naval Training Sys-tems Center

Cherry T (1995) The effectiveness of interactivity on fitnessperformance Unpublished masterrsquos thesis University ofCentral Florida Orlando FL

Clark B amp Malone R D (1952) Topographical orientationin naval aviation cadets Project No NM 001 0590130Pensacola FL US Naval School of Aviation Medicine

Cohen M (1992) Integrating graphic and audio windowsPresence Teleoperators and Virtual Environments 1(4) 468ndash481

Coull T amp Rotham P (1993) Virtual reality for decisionsupport systems AI Expert 8(8) 22ndash25

Crosby T N amp Kennedy R S (1982) Postural disequilib-rium and simulator sickness following flights in a P3-C opera-tional flight trainer Paper presented at the 53rd AnnualAerospace Medical Association Bal Harbor FL

Crystal Rivers Engineering (1995) Snapshot HRTF Measure-ment System Groveland CA

Darken R P amp Sibert J L (1996) Navigating large virtualspaces International Journal of Human Computer Interac-tion 8(1) 49ndash71

Defanti T A amp Brown M D (1991) Visualization in scien-tific computing Advances in Computers 33 247ndash305

Dix A Finlay J Abowd G amp Beale R (1993) Humancomputer interaction New York Prentice Hall

DiZio P amp Lackner J R (1992) Spatial orientation adapta-tion and motion sickness in real and virtual environments

Presence Teleoperators and Virtual Environments 1(3) 319ndash328

Dolezal H (1982) Living in a world transformed Perceptual

and performatory adaptation to a visual distortion NewYork Academic Press

Druckman D amp Bjork A (Eds) (1994) Learning remem-bering believing Enhancing human performance Washing-ton DC National Academy Press

Durlach N I amp Mavor A S (Eds) (1995) Virtual realitymdashscientific and technological challenges Washington DC Na-tional Academy Press

Ebenholtz S M (1988) Sources of asthenopia in navy flight

simulators Alexandria VA Defense Technical InformationCenter (AD-A212699)

Ebenholtz S M (1992) Motion sickness and oculomotorsystems in virtual environments Presence Teleoperators andVirtual Environments 1(3) 302ndash305

Eberts R E (1994) User interface design Englewood CliffsNJ Prentice Hall

Egan D E (1988) Individual differences in human-computer

interaction In M Helander (Ed) Handbook of human-com-puter interaction (pp 543ndash568) Amsterdam NetherlandsNorth Holland

Egan D E amp Gomez L M (1985) Assaying isolating andaccommodating individual differences in learning a complexskill In R F Dillon (Ed) Individual differences in cogni-tion (pp 173ndash217) Orlando Academic Press

Ekstrom R B French J W amp Harman H H (1976)Manual for kit of factor referenced cognitive tests PrincetonEducational Testing Service

Ellis S R (Ed) (1993) Pictorial communications in virtualand real environments (2nd ed) (pp 8ndash10) London Tayloramp Francis

Ellis S R amp Bucher U J (1994) Distance perception ofstereoscopically presented virtual objects optically superim-posed on physical objects by a head-mounted see-throughdisplay Proceedings of the Human Factors Society 38th An-nual Meeting (pp 1300ndash1304) Santa Monica CA HumanFactors Society

Ellis S R amp Menges B M (1995) Judged distance to vir-tual objects in the near visual field Proceedings of the HumanFactors Society 39th Annual Meeting (pp 1400ndash1404) SantaMonica CA Human Factors Society

Esposito C (1995) User interface issues for virtual systemsTutorial at the Virtual Reality Annual International Sympo-sium March 11ndash15 Research Triangle NC

Stanney et al 347

Findlay J M amp Newell F N (1995) Perceptual cues andobject recognition In K Carr and R England (Eds) Simu-lated and virtual realities Elements of perception LondonTaylor amp Francis

Fisher H G amp Freedman S J (1968) The role of the pinnain auditory localization Journal of Auditory Research 815ndash26

Fisk A D amp Rogers W A (1991) Toward an understand-ing of age-related memory and visual search effects Journalof Experimental Psychology 120 131ndash149

Fontaine G (1992) Experience of a sense of presence in in-tercultural and international encounters Presence Teleopera-tors and Virtual Environments 1(4) 482ndash490

Fukui Y amp Shimojo M (1992) Differences in recognitionof optical illusion using visual and tactual sense Journal ofRobotics and Mechatronics 4(1) 58ndash62

Gallistel C R (1990) The organization of learning Cam-bridge MA The MIT Press

Geldard F A (1972) The human senses (2nd ed) New YorkWiley

Gibson J J (1979) The ecological approach to visual percep-tion Boston Houghton Mifflin

Gomez L M Egan D E amp Bowers C (1986) Learningto use a text editor Some learner characteristics that predictsuccess Human-Computer Interaction 2 1ndash23

Greeno J Smith D amp Moore J (1993) Transfer of situ-ated learning In D K Detterman and R J Sterberg (Eds)Transfer on trial Intelligence cognition and instruction (pp99ndash167) Norwood NJ Ablex

Guedry F E (1965) Habituation to complex vestibularstimulation in man Transfer and retention of effects fromtwelve days of rotation at 10 RPM Perceptual and MotorSkills 21 459ndash481

Haber R N amp Hershenson M (1973) The psychology of vi-sual perception New York Holt Rinehart amp Winston

Hendrix C amp Barfield W (1995) Presence in virtual envi-ronments as a function of visual and auditory cues Proceed-ings of the Virtual Reality Annual International Symposiumrsquo95 (pp 74ndash82) Research Triangle Park NC IEEE Press

Hertzog C (1989) Influences of cognitive slowing in agedifferences in intelligence Developmental Psychology 25636ndash651

Hettinger L J Berbaum K S Kennedy R S DunlapW P amp Nolan M D (1990) Vection and simulator sick-ness Military Psychology 2(3) 171ndash181

Hettinger L J Berbaum K S Kennedy R S amp WestraD P (1987) Human performance issues in the evaluation

of a helmet-mounted area-of-interest projector Proceedingsof the IMAGE IV Conference (pp 320ndash327) Phoenix AZImage Society Inc

Hill J W (1967) The perception of multiple tactile stimuli(Report No 4823-1) Palo Alto CA Stanford UniversityStanford Electronics Laboratory

Howard I P (1984) The perception of posture self-motionand the visual vertical In K R Boff L Kaufman and J PThomas (Eds) The handbook of perception and human per-formance Vol 1 (pp 18-1ndash18-62) New York Wiley

Howard I P Ohmi M Simpson W amp Landolt J P(1987) Vection and the spatial disposition of competing mov-ing displays Paper presented at the Aerospace Medical PanelSymposium Brussels Belgium

Jones M B amp Kennedy R S (in preparation) Screening de-sign revisited The work of Charles W Simon RSK Assess-ments Orlando FL

Kaczmarek K Webster J Bach-y-Rita P amp Thompkins W(1991) Electrotactile and vibrotactile displays for sensorysubstitution systems IEEE Transactions on Biomedical Engi-neering 38(1) 1ndash16

Kalawsky R S (1993) The science of virtual reality and vir-tual environments Wokingham England Addison-Wesley

Kallman E A (1993) Ethical evaluation A necessary elementin virtual environment research Presence Teleoperators andVirtual Environments 2(2) 143ndash146

Kennedy R S Fowlkes J E amp Lilienthal M G (1993)Postural and performance changes in Navy and MarineCorps pilots following flight simulators Aviation Spaceand Environmental Medicine 64 912ndash920

Kennedy R S Lane N E Lilienthal M G Berbaum K Samp Hettinger L J (1992) Profile analysis of simulator sick-ness symptoms Application to virtual environment systemsPresence Teleoperators and Virtual Environments 1(3) 295ndash301

Kennedy R S Lanham D S Drexler J M amp LilienthalM G (1995) A method for certification that aftereffects ofvirtual reality exposures have dissipated Preliminary find-ings In A C Bittner and P C Champney (Eds) Advancesin Industrial Ergonomics Safety VII (pp 263ndash270) Taylorand Francis London

Kennedy R S Lilienthal M G Berbaum K S BaltzleyD R amp McCauley M E (1989) Simulator sickness in 10US Navy flight simulators Aviation Space and Environ-mental Medicine 60(1) 10ndash16

Kennedy R S Lilienthal M G Berbaum K S DunlapW P Mulligan B E amp Funaro J F (1987) Guidelines


for alleviation of simulator sickness symptomatology (ReportNo NAVTRASYYCEN TR-87-007) Orlando FL NavalTraining Systems Center

Kennedy R S amp Stanney K M (1996) Postural instabilityinduced by virtual reality exposure Development of a certifi-cation protocol International Journal of Human-ComputerInteraction 8(1) 25ndash47

Kennedy R S Stanney K M Dunlap W P amp Jones M B(1996) Virtual environment adaptation assessment test bat-tery (Report No NAS9-19453) Houston TX NASAJohnson Space Center

Kim W S Tendick F amp Stark L (1993) Visual enhance-

ments in pick-and-place tasks Human operators controllinga simulated cylindrical manipulator In S Ellis (Ed) Picto-rial communication in virtual and real environments (pp182ndash195) London Taylor and Francis

Koenig W (1950) Subjective effects in binaural hearing Jour-nal of the Acoustical Society of America 22(1) 61ndash61

Konz S (1983) Work design industrial ergonomics (2nd ed)New York John Wiley amp Sons

Kozak J J Hancock P A Arthur E amp Chrysler S (1993)Transfer of training from virtual reality Ergonomics 36(7)777ndash784

Krueger M W (1991) Artificial reality (2nd ed) ReadingMA Addison-Wesley

Lackner J (1990) Human orientation adaptation and move-ment control (Tech Report Motion sickness visual displaysand armored vehicle design) (pp 28ndash50) Washington DCBallistic Research Laboratory

Lampton D R Knerr B W Goldberg S L Bliss J PMoshell J M amp Blau B S (1994) The virtual environ-ment performance assessment battery (VEPAB) Develop-ment and evaluation Presence Teleoperators and Virtual En-vironments 3(2) 145ndash157

Lane N E (1986) Issues on performance measurement formilitary aviation with applications to air combat maneuver-ing (Tech Report NTSC TR-86-008) Orlando FL NavalTraining Systems Center

Larijani L C (1994) The virtual reality primer New YorkMcGraw-Hill

Laurel B (1994) Narrative and interaction in PlaceholderComputer Graphics 28(2) 120ndash123

Lee D N (1976) A theory of visual control of braking basedon information about time-to-collision Perception 5 437ndash459

Lestienne F Soechting J amp Berthoz A (1977) Postural

readjustments induced by linear motion of visual scenes Ex-perimental Brain Research 28 363ndash384

Levine O H amp Mourant R R (1994) A driving simulatorbased on virtual environments technology (Tech Report 94-1) Boston Northeastern University Virtual EnvironmentLaboratory

Massimino M J amp Sheridan T B (1993) Sensory substitu-tion for force feedback in teleoperation Presence Teleopera-tors and Virtual Environments 2(4) 344ndash352

Massimino M J amp Sheridan T B (1994) Teleoperator per-formance with varying force and visual feedback HumanFactors 36(1) 145ndash157

McCauley M E amp Sharkey T J (1992) Cybersickness Per-ception of self-motion in virtual environments PresenceTeleoperators and Virtual Environments 1(3) 311ndash318

McConathy D A amp Doyle M (1993) Interactive displays inmedical art In S Ellis (Ed) Pictorial communication invirtual and real environments (pp 97ndash110) London Tay-lor and Francis

McDowall I (1994) 3D Stereoscopic data for immersive dis-plays AI Expert 9(5) 18ndash21

McGovern D E (1993) Experience and results in teleopera-tion of land vehicles In S Ellis (Ed) Pictorial communica-tion in virtual and real environments (pp 182ndash195) Lon-don Taylor and Francis

Meyer K amp Delaney B (1995) Interactivity and VR fasci-nate doctors CyberEdge Journal 5(1) 1ndash7

Middlebrooks J C amp Green D M (1991) Sound localiza-tion by human listeners Annual Review of Psychology 42135ndash159

Middlebrooks J C Makous J C amp Green D M (1989)Directional sensitivity of sound-pressure levels in the humanear canal Journal of the Acoustical Society of America 8689ndash108

Minsky M Ouh-Young M Steele O Brooks F amp Behen-sky M (1990) Feeling and seeing Issues in force displayACM Computer Graphics 24(2) 235ndash243

Mon-Williams M Wann J P amp Rushton S (1993) Bin-ocular vision in a virtual world Visual deficits following thewearing of a head-mounted display Ophthal Physiol Opt13 387ndash391

Nilan M (1992) Cognitive space Using virtual reality forlarge information resource management problems Journalof Communication 42(4) 115ndash135

Occupational Safety and Health Administration (1983) Occu-pational noise exposure Hearing conversation amendmentFederal Register 48 9738ndash9783

Stanney et al 349

Oren T (1990) Designing a new medium In B Laurel(Ed) The art of human-computer interface design (pp 467ndash479) Reading MA Addison-Wesley

Parker D E amp Harm D L (1992) Mental rotation A keyto mitigation of motion sickness in the virtual environmentPresence Teleoperators and Virtual Environments 1(3) 329ndash333

Parker D E amp Parker K L (1990) Adaptation to the simu-lated stimulus rearrangement of weightlessness In G HCrampton (Ed) Motion and Space Sickness (pp 247ndash262)Boca Raton FL CRC Press

Pausch R Crea T amp Conway M (1992) A literature sur-vey for virtual environments Military flight simulator visualsystems and simulator sickness Presence Teleoperators andVirtual Environments 1(3) 344ndash363

Pepper R L Smith D C amp Cole R E (1981) Stereo TVimproves operator performance under degraded visibilityconditions Optics Engineering 20(4) 579ndash585

Peterson F E Lane N E amp Kennedy R S (1965) Therelationship of the Edwardsrsquo Personal Preference Schedule tosuccess in Naval flight training (NAMI-946) Pensacola FLNaval School of Aviation Medicine

Proffitt D R amp Kaiser M K (1995) Human factors in vir-tual reality development Tutorial at the Virtual Reality An-nual International Symposium March 11ndash15 Research Tri-angle NC

Reason J T amp Diaz E (1971) Simulator sickness in passiveobservers Flying Personnel Research Committee Report No1310

Regan C (1993) An investigation into nausea and other side-effects of head-coupled immersive virtual reality VirtualReality 1(1) 17ndash32

Regian J W amp Shebilske W L (1992) Virtual reality Aninstructional medium for visual-spatial tasks Journal ofCommunication 42(2) 136ndash149

Rinalducci E J Mapes D Cinq-Mars S G amp HigginsK E (1996) Determining the field of view in HMDs Apsychophysical method Presence Teleoperators and VirtualEnvironments 5(3) 353ndash356

Robinett W amp Rolland J P (1992) A computational modelfor the stereoscopic optics of a head-mounted display Pres-ence Teleoperators and Virtual Environments 1(1) 45ndash62

Rolland J P Biocca F A Barlow T amp Kancherla A(1995) Quantification of adaptation to virtual-eye locationin see-thru head-mounted displays Virtual Reality AnnualInternational Symposium rsquo95 (pp 56ndash66) Los AlamitosCA IEEE Computer Society Press

Rosenbloom A A amp Morgan M W (1986) Vision and ag-ing General and clinical perspectives New York FairchildPublications

Rushton S Mon-Williams M amp Wann J P (1994) Bin-ocular vision in a bi-ocular world New generation head-mounted displays avoid causing visual deficit Displays15(4) 255ndash260

Russell G amp Miles R (1993) Volumetric visualization of3D data In S R Ellis (Ed) Pictorial communications invirtual and real environments (2nd ed) (pp 131ndash137)London Taylor and Francis

Salthouse T A (1992) Why do adult age differences increasewith task complexity Developmental Psychology 28 905ndash918

Sanders M S amp McCormick E J (1993) Human factors inengineering and design (7th ed) New York McGraw-Hill

Schmidt R amp Young D (1987) Transfer of movement con-trol in motor skill learning In S M Cormier and J D Hag-man (Eds) Transfer of learning Contemporary research andapplications San Diego Academic Press

Scott W B (1991) Computer simulations place models ofhumans in realistic scenarios Aviation Week amp Space Tech-nology 134(25) 64ndash65

Sellen A amp Nicol A (1990) Building user-centered on-linehelp In B Laurel (Ed) The art of human-computer inter-face design (pp 143ndash153) Reading MA Addison-Wesley

Shaw R E Kugler P N amp Kinsella-Shaw J (1990) Reci-procities of intentional systems In R Warren and A HWertheim (Eds) Perception and control of self-motion (pp579ndash619) Hillsdale NJ Lawrence-Erlbaum Associates

Sheridan T B (1993) My anxieties about virtual environ-ments Presence Teleoperators and Virtual Environments2(2) 141ndash142

Sheridan T B (1992) Musings on telepresence and virtualpresence Presence Teleoperators and Virtual Environments1(1) 120ndash126

Shneiderman B (1992) Designing the user interface (2nded) Reading MA Addison-Wesley

Siegel A W (1981) The externalization of cognitive maps bychildren and adults In search of ways to ask better ques-tions In L S Liben A H Patterson and N Newcombe(Eds) Spatial representation and behavior across the lifespan Theory and application (pp 167ndash194) New York Aca-demic Press

Singer M J Witmer B G amp Bailey J H (1994) Develop-ment of lsquopresencersquo measures for virtual environments Posterpresented at the Human Factors Society 38th Annual Meet-ing Nashville TN


Slater M amp Usoh M (1993) Representations systems per-

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ments Presence Teleoperators and Virtual Environments

2(3) 221ndash233

Stanney K M amp Hash P (in press) Locus of user-initiated

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Presence Teleoperators and Virtual Environments

Stanney K M amp Salvendy G (1995) Information visualiza-

tion assisting low spatial individuals with information access

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1184ndash1198

Stanney K M amp Salvendy G (1994) Effects of diversity in

cognitive restructuring skills on human-computer perfor-

mance Ergonomics 37(4) 595ndash609

Steuer J (1992) Defining virtual reality Dimensions deter-

mining telepresence Journal of Communication 42(2) 73ndash93

Stone V E (1993) Social interaction and social development

in virtual environments Presence Teleoperators and Virtual

Environments 2(2) 153ndash161

Stytz M R Frieder G amp Frieder O (1991) Three-dimen-

sional medical imaging algorithms and computer systems

ACM Computing Surveys 23(4) 421ndash496

Thomas J C amp Stuart R (1992) Virtual reality and human

factors Proceedings of the Human Factors Society 36th An-

nual Meeting (pp 207ndash210) Santa Monica CA Human

Factors Society

Thorndyke P W amp Statz C (1980) Individual differences

in procedures for knowledge acquisition from maps Cogni-

tive Psychology 12 137ndash175

Ungs T J (1987) Simulator sickness Evidence of long-term

effects Proceedings of the 31st Annual Human Factors Soci-

ety (pp 505ndash509) Santa Monica CA Human Factors

Society

Vicente K J Hayes B C amp Williges R C (1987) Assay-ing and isolating individual differences in searching a hierar-chical file system Human Factors 29(3) 349ndash359

Viirre E (1994) A survey of medical issues and virtual realitytechnology Virtual Reality World August 16ndash20

Vishton P M amp Cutting J E (1995) Wayfinding displace-ments and mental maps Velocity fields are not typicallyused to determine onersquos aimpoint Journal of ExperimentalPsychology Human Perception and Performance 21(5) 978ndash995

Wann J amp Mon-Williams M (1996) What does virtual real-ity NEED Human factors issues in the design of three-di-mensional computer environments International Journal ofHuman-Computer Studies 44 829ndash847

Welch R B (1978) Perceptual modification Adapting to al-tered sensory environments New York Academic Press

Whiteback C (1993) Virtual environments Ethical issuesand significant confusions Presence Teleoperators and Vir-tual Environments 2(2) 147ndash152

Wickens C D Merwin D H amp Lin E L (1994) Implica-tions of graphics enhancements for the visualization of scien-tific data Dimensional integrality stereopsis motion andmesh Human Factors 36(1) 44ndash61

Williams H P Wickens C D amp Hutchinson S (1994)Fidelity and interactivity in navigational training A compari-son of three methods Proceedings of the Human Factors So-ciety 38th Annual Meeting (pp 1163ndash1167) Santa MonicaCA Human Factors Society

Witkin H A (1950) Individual differences in ease of percep-tion of embedded figures Journal of Personality 19 1ndash15

Wright D L Rolland J P amp Kancherla A R (1995) Us-ing virtual reality to teach radiographic positioning Radio-logic Technology 233ndash240

Zeltzer D (1992) Autonomy interaction and presence Pres-ence Teleoperators and Virtual Environments 1(1) 127ndash132

Stanney et al 351

refining the technologiesrsquorsquo (p 224) We believe human-factors practitioners can assist in making significant con-tributions to the theoretical understanding of human-virtual environment interaction (HVEI) This paper hasorganized the area of human factors research in virtualenvironments (VEs) into three primary subtopics hu-man performance efficiency in virtual worlds health andsafety issues and potential social implications of VEtechnology (See Figure 1) Some of these topics havebeen looked at rather briefly in the past (Thomas amp Stu-art 1992) The objective of the present paper is to pro-vide a comprehensive overview of each of these humanfactors research areas and to provide insight into ap-proaches for their systematic resolution

Designing usable and effective interactive virtualworlds is a new challenge for system developers and hu-man-factors specialists Due to the close bond betweenthe user and the system within VEs it may be impossibleto follow past traditions and segregate human factorsfrom design issues when striving to achieve the potentialof VE technology It is the capabilities and limitations ofthe user that many times will determine the effectivenessof virtual worlds (See Figure 2) An understanding ofhuman-factors issues can thus be used to provide a sys-tematic basis by which to direct future VE research ef-forts aimed at advancing the technology to better meetthe needs of its users In the following sections threeprimary areas of human-factors research in VEs will be

addressed and issues requiring further research will beidentified

2 Human Performance Efficiencyin Virtual Worlds

Computer speed and functionality image process-ing synthetic sound and tracking mechanisms havebeen joined together to provide realistic virtual worldsA fundamental advance still required for VEs to be effec-tive is to determine how to maximize the efficiency ofhuman task performance in virtual worlds In manycases the task will be to obtain and understand informa-tion portrayed in the virtual environment As Wann andMon-Williams (1996 p 845) stated in such cases lsquolsquothegoal is to build (virtual) environments that minimize thelearning required to operate within them but maximizethe information yieldrsquorsquo Maximizing the efficiency of theinformation conveyed in VEs will require developing aset of guiding design principles that enable intuitive andefficient interaction so that users can readily access andcomprehend data The design approach used for moretraditional simulation systems (eg teleoperated sys-tems) was generally lsquolsquotrial and errorrsquorsquo due to the paucityof general non-system-specific design guidelines (Bur-dea amp Coiffet 1994) If VE tasks are designed in suchan ad hoc manner however the potential benefits of the

Figure 1 Areas of human-factors research for virtual environmentsFigure 2 The human factor in virtual environments








Stanney et al 329
















Stanney et al 331














Stanney et al 333



















Stanney et al 335




















Stanney et al 337




















Stanney et al 339




















Stanney et al 341






33 Indirect Effects












Stanney et al 343
















5 Conclusions



Stanney et al 345




Acknowledgments



References






















































Stanney et al 347






























































Stanney et al 349
































2(3) 221ndash233







1184ndash1198















Factors Society







Society












Stanney et al 351







Stanney et al 329
















Stanney et al 331














Stanney et al 333



















Stanney et al 335




















Stanney et al 337




















Stanney et al 339




















Stanney et al 341






33 Indirect Effects












Stanney et al 343
















5 Conclusions



Stanney et al 345




Acknowledgments



References






















































Stanney et al 347






























































Stanney et al 349
































2(3) 221ndash233







1184ndash1198















Factors Society







Society












Stanney et al 351
















Stanney et al 331














Stanney et al 333



















Stanney et al 335




















Stanney et al 337




















Stanney et al 339




















Stanney et al 341






33 Indirect Effects












Stanney et al 343
















5 Conclusions



Stanney et al 345




Acknowledgments



References






















































Stanney et al 347






























































Stanney et al 349
































2(3) 221ndash233







1184ndash1198















Factors Society







Society












Stanney et al 351














Stanney et al 333



















Stanney et al 335




















Stanney et al 337




















Stanney et al 339




















Stanney et al 341






33 Indirect Effects












Stanney et al 343
















5 Conclusions



Stanney et al 345




Acknowledgments



References






















































Stanney et al 347






























































Stanney et al 349
































2(3) 221ndash233







1184ndash1198















Factors Society







Society












Stanney et al 351



















Stanney et al 335




















Stanney et al 337




















Stanney et al 339




















Stanney et al 341






33 Indirect Effects












Stanney et al 343
















5 Conclusions



Stanney et al 345




Acknowledgments



References






















































Stanney et al 347






























































Stanney et al 349
































2(3) 221ndash233







1184ndash1198















Factors Society







Society












Stanney et al 351




















Stanney et al 337




















Stanney et al 339




















Stanney et al 341






33 Indirect Effects












Stanney et al 343
















5 Conclusions



Stanney et al 345




Acknowledgments



References






















































Stanney et al 347






























































Stanney et al 349
































2(3) 221ndash233







1184ndash1198















Factors Society







Society












Stanney et al 351




















Stanney et al 339




















Stanney et al 341






33 Indirect Effects












Stanney et al 343
















5 Conclusions



Stanney et al 345




Acknowledgments



References






















































Stanney et al 347






























































Stanney et al 349
































2(3) 221ndash233







1184ndash1198















Factors Society







Society












Stanney et al 351




















Stanney et al 341






33 Indirect Effects












Stanney et al 343
















5 Conclusions



Stanney et al 345




Acknowledgments



References






















































Stanney et al 347






























































Stanney et al 349
































2(3) 221ndash233







1184ndash1198















Factors Society







Society












Stanney et al 351






33 Indirect Effects












Stanney et al 343
















5 Conclusions



Stanney et al 345




Acknowledgments



References






















































Stanney et al 347






























































Stanney et al 349
































2(3) 221ndash233







1184ndash1198















Factors Society







Society












Stanney et al 351










Stanney et al 343
















5 Conclusions



Stanney et al 345




Acknowledgments



References






















































Stanney et al 347






























































Stanney et al 349
































2(3) 221ndash233







1184ndash1198















Factors Society







Society












Stanney et al 351
















5 Conclusions



Stanney et al 345




Acknowledgments



References






















































Stanney et al 347






























































Stanney et al 349
































2(3) 221ndash233







1184ndash1198















Factors Society







Society












Stanney et al 351




Acknowledgments



References






















































Stanney et al 347






























































Stanney et al 349
































2(3) 221ndash233







1184ndash1198















Factors Society







Society












Stanney et al 351





































Stanney et al 347






























































Stanney et al 349
































2(3) 221ndash233







1184ndash1198















Factors Society







Society












Stanney et al 351






























































Stanney et al 349
































2(3) 221ndash233







1184ndash1198















Factors Society







Society












Stanney et al 351
































2(3) 221ndash233







1184ndash1198















Factors Society







Society












Stanney et al 351

1 humanfactorsissuesin universityofcentralflorida...

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