Chapter 45. Measuring and Managing Presence in Virtual Environments
Wallace Sadowski Jr. and Kay Stanney
University of Central Florida
What has inspired the worlds fascination with virtual reality? Undoubtedly, it is the conceived notion that one can step into a virtual environment (VE), be transported to any desired place, and do things impossible in reality. To the general public, ones virtual experience is limited only by imagination. And in fact, todays VE technology does allow users to have unique experiences, such as standing inside a molecule, which were never before possible. However, it is clear that VE technology has not progressed to the exaggerated level portrayed in movies and books. It is also evident that current VEs are certainly not realistic enough that individuals perceive the virtual world as physical reality. VE technology takes advantage of the fact that people have the ability to "psychologically transport" their "presence" to another place that may not exist in reality. This concept is demonstrated when one becomes engrossed in a book or movie and attends to it to the exclusion of ones surrounding environment. The primary characteristic distinguishing VEs from other means of displaying information is the focus on immersion. VEs add a dimension of physiological immersion by removing as many real world sensations as possible while substituting the sensations that would be imparted if the VE were real.
Immersion, whether physiological or psychological in nature, is intended to instill a sense of belief that one has left the real world and is now "present" in the virtual environment. This notion of being present in the virtual world has been considered central to VE endeavors since its conception (Minsky, 1980). Presence is traditionally thought of as the psychological perception of "being in" or "existing in" the VE in which one is immersed (Heeter, 1992; Sheridan, 1992; Steuer, 1992; Witmer and Singer, 1998). To date, the utility of the presence construct, either to enhance interactive design or human performance, has not been clearly established. This may be due to a lack of concise definitions and effective measures for this construct. This chapter commences by describing the concept of presence, then addresses types of presence, variables that influence presence, approaches of measuring presence, and the effects of presence on performance. The latter may ultimately determine the utility of presence, for without benefits to performance this construct may have little value beyond ephemeral captivation.
There is no clear consensus on how best to define sense of presence (Stanney et. al., 1998). Singer and Witmer (1997) describe presence as a perceptual flow requiring directed attention. They suggest that presence is based on the interaction of sensory stimulation, environmental factors, and internal tendencies. If one feels present in a VE, then they are thought to perceive themselves as being in the computer-generated environment rather than in their actual physical location. Yet, humans may experience varying degrees of presence in the VE, typically dividing attention between the physical world and the virtual world (Singer & Witmer, 1997).
The psychological perception of presence in a VE is primarily thought to be the by-product of the VEs immersive and involving properties (Witmer & Singer, in press). Involvement in a VE is thought to occur when one focuses their energy and attention on a coherent set of stimuli or meaningfully related activities and events presented in the virtual world. Thus, increasing the focus of ones attention on the events portrayed in the VE is suggested to enhance involvement, thereby increasing presence.
There are two differing schools of thought on what constitutes immersion in a VE. Witmer and Singer (1998) define immersion as "a psychological state characterized by perceiving oneself to be enveloped by, included in, and interacting with an environment that provides a continuous stream of stimuli and experiences." They also suggest that factors that affect immersion include isolation from the physical environment, perception of self-inclusion in the VE, natural modes of interaction and control, and the perception of self-movement. Witmer and Singer (1998) suggest that VEs that produce a greater sense of immersion will produce higher levels of presence.
With a different perspective, Slater and Wilbur (1997) define immersion as "the extent to which computer displays are capable of delivering an inclusive, extensive, surrounding, and vivid illusion of reality to the senses of the VE participant." Inclusiveness indicates the extent to which physical reality is shut out. Extensiveness indicates the range of sensory modalities accommodated and stimulated. Surrounding indicates the extent to which the VE is panoramic rather than limited to a narrow field of view. Vividness indicates the resolution and fidelity of stimuli for each modality and is concerned with the richness, information content and the quality of the displays. Slater and Wilbur (1997) suggest that immersion can be an objective and quantifiable description of what any particular system does provide. Based upon these descriptors, Slater and Wilbur characterize immersion as primarily determined by the extent to which devices and displays are capable of replicating the physiological sensations of the real world equivalent of the VE in which the person is interacting.
Regardless of how immersion is defined in regards to virtual environments, it is generally accepted that "presence" is moderated by both external factors (Barfield and Hendrix, 1995; Prothero and Hoffman, 1995; Hendrix and Barfield, 1996a, 1996b; Welch et al., 1996; Slater and Wilbur, 1997), as well as internal factors (Fontaine, 1992; Heeter, 1992; Witmer and Singer, 1998). Arguably, one must be afforded both forms of immersion to maximize the likelihood of high levels of presence. In other words, one must be sufficiently immersed through the VE systems hardware components and ergonomic design to enable the psychological leap of feeling "present" in the virtual environment. Regardless of the realism of the VE, if one is distracted by, or has psychological ties to, the external world the sensation of presence may never occur and certainly will not develop to a great degree. To better understand this construct, it is important to realize that there are several different types of presence that can be elicited in a virtual environment.
Types of Presence
Heeter (1992) asserts that there are three different types of presence: environmental, social and personal. Environmental presence is described as the extent to which the environment itself appears to acknowledge your existence and reacts to you. Heeter contends that many VEs are unresponsive to users. The premise of social presence is simply that, if multiple people are immersed in the same VE, the presence of others provides further evidence that the environment exists and thus each participant is more prone to experience higher levels of presence. Correspondingly, a study at the BattleTech Center, a VE entertainment facility in Chicago, found that 305 of 312 respondents to a questionnaire indicated a preference to play against other humans or humans and computers when playing VE games (see Heeter, 1992). This implies that there is a desire to experience social interaction in these environments. Personal presence is a measure of the extent to which, and the reasons why, one feels like they are "in" the VE. The degree to which individuals feel present in VEs varies tremendously and may never be fully understood or predictable without a comprehensive and accurate measure of presence. In order to accurately measure presence it is essential to determine the factors that influence it.
Variables That Influence Presence
Just as there are many forms of presence, from environmental to social to personal, there are multiple variables that influence these forms of presence. Both individual and system variables are thought to influence the level of presence experienced in a virtual environment (Stanney, et al., 1998). Some specific variables discussed include: 1) ease of interaction, 2) user-initiated control, 3) pictorial realism, 4) length of exposure, 5) social factors, and 6) system factors. Beyond these specific variables, Slater and Usoh (1993a) distinguish between internal and external factors that may contribute to a participants sense of presence.
Ease of interaction: VE users that experience difficulties navigating through or interacting with the environment, or while performing a task, will be more likely to perceive the VE as unnatural and may experience less presence in the environment. Weghorst and Billinghurst (1993) manipulated the design of VE systems, influencing the ease of interaction, and found those environmental designs which facilitated the "ease of interaction" increased the reported sense of presence in the VE.
User-initiated control: Witmer and Singer (1994) suggest that the greater the level of control a user has, regarding their actions in a VE, the higher the reported level of presence. Witmer and Singer explain that this control factor is driven by the immediacy of the systems response, the correspondence of user-initiated actions, and by the naturalness of the mode of control. Sheridan (1992) suggests that a users "control of the relation of sensors to the environment" (e.g. the ability to modify one's viewpoint) and their ability to modify the physical characteristics of the VE are two of the "principle determinants" of sense of presence. Welch, Blackmon, Liu, Mellers, and Stark (1996) found that subjects indicated that interactivity (i.e. being the driver versus the passenger) played a greater role than scene complexity in their judgements of relative presence.
Pictorial realism: Witmer and Singer (1994) suggest that presence should increase as a function of the pictorial realism of the environment. Pictorial realism, in this case, relates to the connectedness, continuity, consistency, and meaningfulness of the perceptual stimuli presented. Welch et al. (1996) found limited, but positive influences of pictorial realism on presence. Wilson, Nichols, and Haldane (1997) found that realistic visual depth cues were positively related to reported levels of presence.
Length of Exposure: The effect on presence based on the amount of time spent in a VE is currently unknown. However, extending the amount of time spent in a VE may increase presence because it enhances other factors thought to have an effect. These factors include practice with VE tasks, the extent of familiarity within the VE, and the level of sensory adaptation to the intersensory and sensorimotor discordances presented by the VE (Welch et al., 1996). If prolonged VE exposure results in increased simulator sickness symptoms presence could be negatively affected (Kennedy, Stanney, & Dunlap, in press). Witmer and Singer (1998) report that combining data from four experiments resulted in a correlation between simulator sickness and presence of 0.426, p<.001. Witmer and Singer (1998) suggest that symptoms accompanying simulator sickness draw attention away from the VE and focus that attention inward, decreasing involvement in the VE and thereby reducing the sense of presence. Similarly, in a recent study using a maze shaped VE and exposures up to one hour in length, subjective presence was found to be negatively correlated (r = -0.342, p<0.001) with sickness (Stanney, 1999). Of the factors that can impede sense of presence, cybersickness may be one of the most deleterious and thus exposure durations should be set such that they minimize such adverse effects.
Social factors: There is growing interest in the effects of social factors on presence (Steuer, 1992; Heeter, 1992). The premise of "social presence" is that if other people (i.e. representative avatars) reside in the VE there is more evidence that the VE exists. Correspondingly, if the other persons in the VE essentially acknowledge one's presence in the VE it offers further affirmation that one actually "exists" in that environment (Heeter, 1992). Social presence may result from communicating with others verbally or by gestures, interacting with others in the environment, or through confirmation that others recognize their existence in the environment.
Internal factors: Slater and Usoh (1993a) describe internal factors as the individual differences in how an individual cognitively processes the information provided by the VE experience. While these factors are difficult to influence, it is important to understand their influence on presence.
Slater and Usoh (1993a) used a technique known as Neurolinguistic Programming (NLP) to assess how internal factors affect virtual presence. The NLP model suggests that subjective experience is encoded in terms of three main representation systems: visual, auditory, and kinesthetic (VAK). Practitioners of NLP claim that people have a tendency to prefer one representation system over another in a given context. The visual system includes external images, as well as remembered or constructed internal mental images. The auditory system includes external sounds and remembered or contrived internal sounds. Also included in the auditory system is internal dialogue (i.e. a person talking to themselves on the inside). The kinesthetic system includes tactile sensations caused by external forces acting on the body and emotional responses (specific to internal tactile and haptic sensations).
The Slater and Usoh (1993a) study suggests that visually dominant people report greater levels of presence than individuals whose primary representational system is auditory or kinesthetic and that a person who tends to process information more from the first position (e.g. "I" or "my") is more likely to experience a sense of presence than those who process more from the second or third position. They also suggest that the higher the proportion of visual predicates and references used when describing the VE experience (e.g. "looking" or "seeing"), the greater the reported sense of presence, while the higher the proportion of auditory predicates and references the lower the reported sense of presence. For those individuals provided with a virtual body (VB) the greater the proportion of kinesthetic references and predicates the higher the reported level of presence. For those without a VB kinesthetic references were inversely related to presence. It should be cautioned that these results were derived from a VE that stimulated primarily the visual system, with only a small amount of associated sound and no haptic interface. The critical issue is that subjective experience is encoded in terms of different representation systems and that people may prefer one representation system over another. Thus, it is important to consider the types of individuals who will use a given VE system and their preferred representational system.
System factors: Slater and Usoh (1993a) describe system factors as external factors that relate to how well the system replicates the real world equivalent, how this information is presented to the user, and the how the user interacts with the VE. External factors are determined wholly by the VE hardware and the software that drives the display. Slater and Usoh suggest external factors that may influence reported levels of presence include high quality, high-resolution information being presented to the participants sensory organs in a manner that does not convey the existence of the devices or displays. The environment that is being presented to the participant should be consistent across all sensory information displays. The environment should be one in which the participant can interact with objects and other actors, and one that reacts to the user. They also suggest that the self-representation of the participant should include a virtual body (VB) that is similar in appearance to the participants own body, and responds appropriately to the participants movements.
In a study of system factors, Hendrix and Barfield (1996a) found that the addition of stereopsis positively influenced spatial realism during interaction within the VE and resulted in reports of greater presence. The same study also found that adding head-tracking and manipulating the geometric field of view (GFOV) influenced reported levels of presence, with head-tracking and larger GFOVs associated with higher levels of presence. Barfield and Hendrix (1995) found that presence was enhanced with increasing update rates but was approximately constant between 15Hz-20Hz. Welch et al. (1996) also encountered a negative influence on presence when a delay in visual feedback occurred.
Currently, most VEs focus primarily on visual and auditory stimulation. Hendrix and Barfield (1996b) found that spatialized sounds had a significant effect on presence when compared to non-spatialized or no sounds at all. It has also been suggested that as more sensory modalities are stimulated presence should increase (Sheridan, 1992). Sadowski (1999) reviewed olfactory stimulation in VEs and the potential of incorporating odors as a means of increasing presence and performance in VEs. The results of this review indicated that utilizing olfactory cues in VEs might serve to facilitate performance on tasks especially those demanding recall or recognition. The human olfactory system utilizes the sensation of odors for detection, recognition, discrimination, and differentiation/scaling (Barfield and Danas, 1996). Furthermore, neuroanatomically, in comparison to the visual and auditory systems, the olfactory system has many direct connections to the limbic system of the brain where emotions and affects are regulated (Kandel and Schwartz, 1985). There is strong evidence that odors can be effective in manipulating mood, increasing vigilance, decreasing stress and improving recall and retention of learned materials (Youngblut, Johnson, Nash, Wienclaw, and Will, 1996). Knasko and Gilbert (1990) found that even the suggestion of odor affects reported levels of pleasure and mood. Thus, the powerful influences of the olfactory system can be manipulated by incorporating odors in a VE to produce a more realistic experience, thereby, increasing levels of presence and enhancing performance on some tasks.
Another system factor to consider is the interplay of the ergonomic design of the VE hardware. Weghorst and Billinghurst (1993) found display comfort and quality to be predictive of reported presence. If the user is distracted by or must focus on the VE hardware because it is uncomfortable or burdensome the ability to simulate "being in" the VE may deteriorate (Slater and Usoh, 1993a).
From the review of factors that influence presence general guidelines can be provided that, if effectively implemented, should enhance users' presence in virtual environments (see Table 1).
Table 1. Guidelines for Supporting Presence
Ease of Interaction
|Provide seamless interaction such that users can readily orient in, traverse in, and interact with the virtual environment.||Poorly designed interaction takes focus away from the experience and places it instead on motion/mechanics.|
|Provide immediacy of system response, correspondence of user-initiated actions, and a natural mode of control.||Delays, discordance of users versus effectors actions, and unnatural control devices hinder engagement in the VE.|
|Provide continuity, consistency, connectedness & meaningfulness in presented stimuli.||Poorly designed visual interaction hinders engagement in the VE.|
Length of Exposure
|Provide sufficient exposure time to provide VE task proficiency, familiarity with the VE, and sensory adaptation.||Avoid unnecessarily prolonged exposures that could exacerbate cybersickness.|
|Provide opportunities to interact with and communicate with others verbally or by gestures. Provide confirmation that others recognize one's existence in the VE.||If one's presence in the VE is not acknowledged by others it may hinder the perception that they "exist" in that environment.|
|Identify the types of individuals who will use a VE system and their preferred representational system (i.e., visual, auditory, kinesthetic).||Individual differences can render VE systems differentially effective.|
|Providing stereopsis, head-tracking, a large field of view, increasing update rates, multi-modal interaction, and ergonomically sound sensors/ effectors facilitate presence.||Poorly designed systems can degrade the users' experience. Note: This does not suggest that the "ultimate" experience is required, but rather what is provided should be well designed and developed.|
Although the benefits of presence have been widely discussed and touted, few researchers have attempted to systematically measure this concept and relate it to possible contributing factors. It could be that sense of presence is simply an epiphenomenon of good VE design or potentially even a distraction (Ellis, 1996). Without a valid measure of presence, however, this issue cannot be resolved. Determining how to measure presence may provide a means to establish whether presence does indeed enhance VE system interaction and a greater understanding of the factors that drive this phenomenon may result.
A valid measure of presence should be; (a) Relevant have a direct connection with presence and its components; (b) Reliable have proven test-retest repeatability; (c) Sensitive have sensitivity to variations in the variables affecting presence; (d) Non-intrusive to avoid unintentional degradation of performance and/or sense of presence; and (e) Convenient portable, low cost, and easy to learn and administer (Jex, 1988; Hendrix and Barfield, 1996a).
Presence may be subjective or behavioral in nature. Subjective presence may be measured by response to questions regarding the extent to which the participant senses "being in" the VE. Many VE researchers have attempted to measure presence through subjective reports and/or subjective ratings (Slater, Usoh, & Steed, 1994; Prothero & Hoffman, 1995; Hendrix & Barfield, 1996; Welch, et al., 1996; Witmer & Singer, 1998). Behavioral presence relates to internally measurable or externally observable responses to the VE and the presented stimuli. Behavioral or physiological measures, typically more objective in nature, have also been used to measure presence in virtual environments (Wilson, Nichols & Haldane, 1997; Cohn, DiZio & Lackner, 1996).
Subjective Measures of Presence
Subjective measures of presence include such psychological measurement instruments as; (a) rating scales (e.g., "On a scale of 1-7 rate how natural did your interactions with the virtual environment seem?"); (b) subjective reports (e.g., "I really felt like I was in another place and forgot that I was actually in a laboratory."); (c) the method of paired-comparisons (e.g., "In which of the two virtual environments did you feel most present?"); (d) magnitude estimation ("If the naturalness of the real world is equal to 100, please rate this VE on a scale of 1-100 for naturalness."); and (e) cross-modality matching (e.g., "Make this music as loud as the strength of the presence you experienced in the VE with maximum music volume being equal to the highest possible presence.").
Rating Scales - Subjective rating scales have been used in several VE research experiments to evaluate the amount of presence experienced by participants (Slater, Usoh, & Steed, 1994; Prothero and Hoffman, 1995; Witmer and Sadowski, 1998). Witmer and Singer (1998) developed the Presence Questionnaire (PQ), which measures presence along three subscales: (a) involvement and control, (b) naturalness, and (c) interface quality. Witmer and Singer (1998) have data from several experiments that indicate that the PQ is a reliable and valid measure of presence (see Slater, in press; Singer & Witmer, in press). The PQ also has shown evidence of meaningful relations with learning, aftereffects, and performance.
Subjective Reports - Some VE experiments have also incorporated subjective reports as a means of obtaining information regarding presence (Slater and Usoh, 1993b; Hendrix and Barfield, 1996a). These studies used directed, but open-ended, questions to elicit participants reactions and impressions related to presence. Since these answers were formed in the participants own words it may serve to reduce any bias from question interpretation and Likert scale response bias.
Method of Paired-Comparisons - Schloerb (1995) proposed a paired-comparisons procedure in which the participants task is to distinguish between a real-world scene and a VE simulating the same scene. Hence, if participants are unable to distinguish between the two environments, one could reasonably suggest that their sense of presence in the VE should be as strong as in the real world. Given the present state of VE technology it is unlikely that any participants would not be able to distinguish the difference between a computer-generated VE and the real-world environment. Therefore, this method may be more effective in comparing VEs amongst each other to determine which aspects of each environment, and which environment as a whole, has the greatest influence on facilitating or degrading presence. Welch, et al. (1996) used the method of paired comparison to determine the influence of three variables on participants presence. Participants were presented with a pair of VEs that differed from each other in respect to; a) whether the participant had an interactive or passive exposure, b) whether the VE had high or low levels of pictorial realism, and c) whether there was a short (200msec) or long (1700msec) delay of visual feedback. After participants viewed each pair of VEs they reported which VE produced more presence and indicated this difference on a scale of 1-100. The results of Welch et al. (1996) are reported above. The paired comparisons method has the advantage that it does not require investigators to explain to participants what is meant by the concept of presence (Stanney, et. al., 1998). Unlike subjective reports and rating scales, which must often define or describe what is meant by terms, the method of paired comparisons requires simple comparisons among alternatives. The benefit is that the response bias created by defining terms is avoided. There is an issue with this method in that the size of the difference that is detectable (known as the "just noticeable difference") will be dependent on the aspects of the stimuli (i.e., the real scene versus the VE) that are compared. It is likely that individuals will be far more sensitive to differences in some dimensions (e.g., VE system lag versus real-time response from the real scene) as opposed to others (e.g., poor stereo sound in the VE).
Cross-Modality Matching (CMM) - The scaling of sensory experiences, or psychophysics, emerged in the late 19th century. Today sensory psychophysical scales are universally used and accepted in experimental psychology and tend to be reliable and stable (Stanney et al., 1998). The premise of CMM is that a person can monotonically represent the experiences of one sensory modality through another modality by producing a subjectively equal representation using a measure of the second sensory modality. This method is particularly effective when a concept does not readily lend it self to verbal scaling (such as when a definition of terms leads to response bias). Individual differences in representation of sensory modalities, however, can be problematic as it can lead to high response variability. For example, a person can characterize increasing or decreasing changes in a visual stimulus (e.g. light intensity), as they perceive them, by matching these increases or decreases with an auditory stimulus (e.g. auditory intensity). Hence, it seems reasonable that the CMM technique could be utilized to provide an indicator of the overall presence experienced in a VE or utilized to determine which portion(s) of a VE provided the most influence on presence.
Subjective measures of presence have the advantages of being generally easy to administer and interpret. However, the major drawback of subjective measures is the problem of inter-rater reliability. The participants must understand the concept of what presence "is" and interpret the questions uniformly. Psychometric developers must ensure that the measurement tool is measuring "presence" as a whole, and not only factors that contribute to it. As presence is still an emerging phenomenon there are many questions still to be answered regarding what this construct "is" and how to measure it with subjective measurement tools. More objective measures of presence, such as physiological and behavioral measures, may be helpful in determining which individual and system factors influence presence.
Objective Measures of Presence
Because people commonly experience physiological or behavioral responses to stimuli in the real world, it seems reasonable to conclude that stimuli in an immersive VE may also produce such responses. These responses may include reflexive motor acts and physiological indicators (physiometric and neurophysiological changes). These responses could be objectively measured without participant bias and used as a primary or secondary indicator of environmental influences on perceived presence in the VE.
Reflexive Motor Acts - First suggested by Held and Durlach (1987), measuring behaviors, such as "startle responses" (i.e. ducking or flinching), could provide indicators of presence in a VE. Wilson, Nichols, and Haldane (1997) used startle responses to an unexpected event and awareness of background music to assess presence. Other types of behaviors such as reaching for a virtual object, greeting virtual avatars, orienting responses, head positioning, or avoiding virtual hazards (i.e. visual cliffs) may suggest that participants "believe" they occupy the virtual space. Physiological and behavioral measures may be most useful when they are tailored to the experiences participants are expected to have in a VE. For example, Cohn, DiZio, and Lackner (1996) demonstrated that participants responded with an automatic motor response (used as a measure of presence) in a VE designed to induce a sense of body rotation.
Physiological Measures Physiological indicators including muscular tension, cardiovascular responses, and ocular behaviors have been suggested as presence measures (Barfield & Weghorst, 1993). Bioelectric information can be obtained by electromyography (EMG), electroencephalograms (EEGs), galvanic skin response (GSR) sensors, and measures of skin temperature. Measures of visual system behavior may provide a wealth of information regarding attention, alertness and arousal. Pupilometry, eye-trackers, and electrooculograms (EOGs) have the potential to be useful tools in the isolation of presence invoking stimuli. These visual indicators may serve to identify which elements of the VE capture attention or evoke physiological changes in the person immersed. This physiological information may provide information regarding the effects of specific environmental stimuli or events experienced in a VE. Strickland and Chartier (1997), although not directly investigating presence, have demonstrated the ability to utilize EEG measurements in a head mounted display. Measuring and interpreting the differences in cortical responses in real and virtual environments may lead to a better understanding of the effects of various software and hardware influences in a virtual environment.
The drawback of many behavioral and physiological measures of presence is that collecting the data can be intrusive, difficult to obtain, and they are frequently unreliable. An objective measure of presence that can provide quantifiable differences between baseline measures, or can be compared to real world situations, would be ideal. However, ensuring that the physiological or behavioral responses are "directly related" to the level of presence being experienced in the VE is difficult at best. Due to the inherent weaknesses in both types of measures, it would be preferable to utilize a combination of subjective and objective measures of presence to obtain a comprehensive understanding of the influences on presence in VEs.
Table 2 provides a summary of the currently available presence measures, their strengths and their weaknesses.
Table 2. Measures of Presence.
Type of Measure
Description of Measure
|Rate level of presence experienced in VE||Direct perception of user||Inter-rater reliability may be weak|
|Directed, open-ended questions of reactions and impressions related to presence||Direct perception of user||Interpreting results may be difficult due to response variability|
|Method of Paired Comparisons||
|Distinguish between a real world scene and a VE simulating that scene or between alternative VE systems||No bias due to description of definition of terms||The size of the just-noticeable is dependent on stimulus characteristic compared|
|Cross Modality Matching||
|Represent experience of one sensory modality through another modality||Can be used when verbal scaling is inappropriate or difficult to quantify||Interpreting results may be difficult due to response variability|
|Reflexive Motor Acts||
|Unintentional physical reactions or behaviors evoked by stimuli in, or events occurring in, the VE.||Directly influenced by the VE. No subjective bias.||May not reflect influences of the stimuli or events on total presence.|
|Physiological responses that occur when experiencing the VE stimuli or events occurring within it.||Can serve to isolate influences on presence and be objectively measured.||Internal or external "noise" may affect the measures. Intrusiveness and reliability problems.|
Relationship between Presence and Task Performance
Stanney et al. (1998, p. 164) suggest that while the necessity of presence to support performance in a VE is presently unclear, "the potential relation (1) has considerable face validity, (2) is suggested by perceptual and cognitive theories that indicate that positive transfer increases with the level of original learning as long as structurally similar stimuli and responses are available and required for both the training and transfer tasks (Schmidt & Young, 1987), and (3) is supported by early but limited empirical evidence (Bailey & Witmer, 1994; Witmer & Singer, 1994)." These issues provide the impetus to explore this relationship more fully. Performance on several VE tasks has been shown to be positively related to subjective presence, including tracking performance (Ellis, Dorighi, Menges, Adelstein, & Jacoby, 1997), search task performance (Pausch, Proffitt, and Williams, 1997), as well as performance on a sensorimotor tasks (Maida, Aldridge and Novak, 1997). Some studies have found psychomotor task performance to be positively related to subjective presence (Witmer & Singer, 1994), while others have not (Singer, Ehrlich, Cinq-Mars, & Papin, 1995). Similarly, spatial knowledge has been found to be positively related to presence in one study (Singer, Allen, McDonald & Gildea, 1997), but not in another (Bailey and Witmer, 1994).
In a recent study of performance on a battery of tasks modeled after the Virtual Environment Performance Assessment Battery (VEPAB, Lampton, Knerr, Goldberg, Bliss, Moshell, & Blau, 1994), subjective presence was found to be positively correlated with both task performance and the amount of movement (i.e., yaw and roll) experienced throughout the VE interaction (Stanney, 1999). Taken together, these studies provide early evidence that performance may indeed be positively related to presence. Greater study is needed, however, to fully characterize this relationship, with particular attention being warranted for the task specific influences of presence. While designers often aspire to create the ultimate in reality, VE systems should only be expressly designed to engender high levels of presence when the causal relationship between presence and a given VE task is empirically validated.
While there has been considerable discussion of the concept of presence, the utility of this construct has yet to be definitively determined (Stanney, et. al., 1998). There are even those who suggest that there is little utility to this construct and its relationship to performance. For some training tasks, presence may be desirable, but not necessary. For other training tasks, facilitating presence may be an asset by increasing realism and potentially aiding the positive transfer of training. It is clear that with the current short-coming of valid measures of presence, the fundamental research required to determine the inherent worth of this construct will be difficult to conduct properly. Stanney et. al. (1998) suggest that presence may be intimately related to certain VE attributes, such as interactivity and involvement, which seem to be vital components in the creation of believable if not "realistic" virtual worlds. Thus, for certain purposes, the challenge may be to determine how best to improve the effectiveness and quality of the VE experience, rather than striving for the ultimate in presence. However, in the entertainment industry the goal of increasing the sense of presence in VEs will undoubtedly continue to be a highly desirable feature to developers and consumer gamers. For all practical purposes, presence and immersion may be the most valuable benefits that VE offers the entertainment industry and its clients.
Bailey, J.H. and Witmer, B.G. (1994). Learning and transfer of spatial knowledge in a virtual environment. Proceedings of the Human Factors & Ergonomics Society 38th Annual Meeting (pp. 1158-1162). Santa Monica, CA: Human Factors & Ergonomics Society.
Barfield, W., & Danas, E. (1996). Comments on the use of olfactory displays for virtual environments. Presence: Teleoperators and Virtual Environments, 5(1), 109-121.
Barfield, W. & Hendrix, C. (1995). The effect of update rate on the sense of presence within virtual environments. Virtual Reality: The Journal of the Virtual Reality Society, 1(1), 3-16.
Barfield, W. & Weghorst, S. (1993). The sense of presence within virtual environments: A conceptual framework. In G. Salvendy & M. Smith (Eds.), Human-computer interaction: Software and hardware interfaces (pp. 699-704). Amsterdam: Elsevier.
Cohn, V., DiZio, P., & Lackner, J. (1996). Reaching movements during illusory self-rotation show compensation for expected Coriolis forces. Society for Neuroscience Abstracts, 22(1), 654.
Ellis, S.R., Dorighi, N.S., Menges, B.M., Adelstein, B.D., and Jacoby, R.H. (1997). In search of equivalence classes in subjective scales of reality. In M. Smith, G. Salvendy, and R. Koubek (Eds.), Design of computing systems: Social and ergonomic considerations (pp. 873-876). Amsterdam, Netherlands: Elsevier Science Publishers, San Francisco, CA, August 24-29.
Fontaine, G. (1992). Experience of a sense of presence in intercultural and international encounters. Presence: Teleoperators and Virtual Environments, 1(4), 482-490.
Held, R., & Durlach, N. (1987). Telepresence, time delay and adaptation. NASA Conference Publication 10032, chapter 28.
Held, R., & Durlach, N. (1992). Telepresence. Presence: Teleoperators and Virtual Environments, 1(1), 109-112.
Heeter, C. (1992) Being There: The subjective experience of presence. Presence: Teleoperators and Virtual Environments, 1(2), 262-271.
Hendrix, C., & Barfield, W. (1996a). Presence within virtual environments as a function of visual display parameters. Presence: Teleoperators and Virtual Environments, 5(3), 274-289.
Hendrix, C., & Barfield, W. (1996b). The sense of presence within auditory environments. Presence: Teleoperators and Virtual Environments, 5(3), 290-301.
Jex, H. (1988). Measuring mental workload: Problems, progress, and promises. In Hancock, P.A. & Meshkati, N. (Eds.) Human Mental Workload. Amsterdam, Netherlands: North-Holland.
Kandel, E., & Schwartz, J. (1985). Principles of Neural Science. New York: Elsevier.
Kennedy, R., Stanney, K., & Dunlap, W. (in press). Duration and exposure to virtual environments: Sickness curves during and across sessions. Presence: Teleoperators and Virtual Environments.
Knasko, S. & Gilbert, A. (1990). Emotional state, physical well-being, and performance in the presence of feigned ambient odor. Journal of Applied Social Psychology, 20(16), 1345-1357.
Lampton, D.R., Knerr, B.W., Goldberg, S.L., Bliss, J.P., Moshell, J.M., and Blau, B.S. (1994). The virtual environment performance assessment battery (VEPAB): Development and evaluation. Presence: Teleoperators and Virtual Environments, 3(2), 145-157.
Maida, J., Aldridge, A., and Novak, J. (1997). Effects of lighting on human performance in training. In M. Smith, G. Salvendy, and R. Koubek (Eds.), Design of computing systems: Social and ergonomic considerations (pp. 877-880). Amsterdam, Netherlands: Elsevier Science Publishers, San Francisco, CA, August 24-29.
Minsky, M. (1980). Telepresence. Omni, June, 45-51.
Nichols, S., Haldane, C., & Wilson, J. (1997) Measurement of presence and side effects in virtual environments (Rep. VIRART/97/148). Nottingham, England: University of Nottingham, Virtual Reality Applications Research Team.
Pausch, R., Proffitt, D., and Williams, G. (1997). Quantifying immersion in virtual reality. Computer Graphics Proceedings, Annual Conference Series/ ACM SIGGRAPH (pp. 13-18). Los Angeles, CA: ACM SIGGRAPH.
Prothero, J. & Hoffman, H. (1995). Widening the field-of-view increases the sense of presence within immersive virtual environments (Human Interface Technology Laboratory Tech. Rep. R-95-4). Seattle: University of Washington.
Sadowski Jr., W. (1999, May). Special Report: Utilization of olfactory stimulation in virtual environments. VR News, 8(4), 18-21.
Schmidt, R. and Young, D. (1987). Transfer of movement control in motor skill learning. In S.M. Cormier and J.D. Hagman (Eds.), Transfer of learning: Contemporary research and applications (pp. 47-79). San Diego: Academic Press.
Sheridan, T. (1992). Musings on telepresence and virtual presence. Presence: Teleoperators and Virtual Environments, 1(1), 120-125.
Singer, M.J., Allen, R.C., McDonald, D.P., and Gildea, J.P. (1997). Terrain appreciation in virtual environments: Spatial knowledge acquisition (Technical Report 1056). Alexandria, VA: U.S. Army Research Institute for the Behavioral and Social Science.
Singer, M.J., Ehrlich, J., Cinq-Mars, S., and Papin, J. (1995). Task performance in virtual environments: Stereoscopic vs. Monoscopic displays and head-coupling (Technical Report 1034). Alexandria, VA: U.S. Army Research Institute for the Behavioral and Social Science.
Singer, M.J. and Witmer, B.G. (1997). Presence; Where are we now? In M. Smith, G. Salvendy, and R. Koubek (Eds.), Design of computing systems: Social and ergonomic considerations (pp. 885-888). Amsterdam, Netherlands: Elsevier Science Publishers, San Francisco, CA, August 24-29.
Singer, M. & Witmer, B. (In Press). On selecting the right yardstick. Presence: Teleoperators and Virtual Environments.
Slater, M. (In Press). Measuring Presence: A response to the Witmer and Singer Presence Questionnaire. Presence: Teleoperators and Virtual Environments.
Slater, M. & Usoh, M. (1993a). Representations systems, perceptual position, and presence in Virtual Environments. Presence: Teleoperators and Virtual Environments, 2(3), 221-233.
Slater, M. and Usoh, M. (1993b) The influence of a virtual body on presence in immersive virtual environments. Virtual Reality International - Proceedings of the Third Annual Conference on Virtual Reality. London: Meckler.
Slater, M., Usoh, M. and Steed, A. (1994). Steps and ladders in virtual reality. ACM Proceedings of VRST '94 Virtual Reality Software and Technology. Singapore: World Scientific Publishing Company.
Slater, M. & Wilbur, S. (1997) A framework for immersive virtual environments (FIVE): Speculations on the role of presence in virtual environments. Presence: Teleoperators and Virtual Environments, 6(6), 603-616.
Stanney, K.M. (1999). Unpublished research data. University of Central Florida, Orlando, FL.
Stanney, K.M., Salvendy, G., Deisigner, J., DiZio, P., Ellis, S., Ellison, E., Fogleman, G., Gallimore, J., Hettinger, L., Kennedy, R., Lackner, J., Lawson, B., Maida, J., Mead, A., Mon-Williams, M., Newman, D., Piantanida, T., Reeves, L., Riedel, O., Singer, M., Stoffregen, T., Wann, J., Welch, R., Wilson, J., Witmer, B. (1998). Aftereffects and sense of presence in virtual environments: Formulation of a research and development agenda. Report sponsored by the Life Sciences Division at NASA Headquarters. International Journal of Human-Computer Interaction, 10(2), 135-187.
Steuer, J. (1992). Defining Virtual Reality: Dimensions determining telepresence. Journal of Communication, 42(2), 73-93.
Stevens, S. (1951). Mathematics, measurement and psychophysics. In S.S. Stevens (Ed.), Handbook of experimental psychology (pp. 1-49). New York: Wiley.
Strickland, D. & Chartier, D. (1997). EEG measurements in a virtual reality headset. Presence: Teleoperators and Virtual Environments, 6(5), 581-589.
Weghorst, S. & Billinghurst, M. (1993). Spatial perception of immersive virtual environments (HIT Lab Tech. Rep.). University of Washington, Seattle.
Welch, R., Blackmon, T., Liu, A., Mellers, B., & Stark, L. (1996). The effects of pictorial realism, delay of visual feedback, and observer interactivity on the subjective sense of presence. Presence: Teleoperators and Virtual Environments, 5(3), 263-273.
Wilson, J., Nichols, S. & Haldane, C. (1997). Presence and side effects: Complementary or contradictory? In M. Smith, G. Salvendy, & R. Koubek (Eds.), Design of computing systems: Social and ergonomic considerations (pp. 889-892). Amsterdam: Elsevier.
Witmer, B., & Sadowski Jr., W. (1998). Non-visually guided locomotion to a previously viewed target in real and virtual environments. Human Factors Special Section on Virtual Environments: Models, Methodology and Empirical Studies, 40(3), 478-488.
Witmer, B. & Singer, M. (1994). Measuring immersion in virtual environments (Tech. Rep. 1014) Alexandria, VA: U.S. Army Research Institute for the Behavioral and Social Sciences.
Witmer, B. & Singer, M. (1998). Measuring presence in virtual environments: A Presence Questionnaire. Presence: Teleoperators and Virtual Environments, 7(3), 225-240.
Youngblut, C., Johnson, R., Nash, S., Wienclaw, R., & Will, C. (1996). Review of virtual environment interface technology. Institute for Defense Analysis IDA Paper P-3186. Available: http://www.hitl.washington.edu/scivw/IDA.