Showing papers in "Presence: Teleoperators & Virtual Environments in 2003"

Toward a more robust theory and measure of social presence: review and suggested criteria

Abstract: At a time of increased social usage of net and collaborative applications, a robust and detailed theory of social presence could contribute to our understanding of social behavior in mediated environments, allow researchers to predict and measure differences among media interfaces, and guide the design of new social environments and interfaces. A broader theory of social presence can guide more valid and reliable measures. The article reviews, classifies, and critiques existing theories and measures of social presence. A set of criteria and scope conditions is proposed to help remedy limitations in past theories and measures and to provide a contribution to a more robust theory and measure of social presence.

The effect of the agency and anthropomorphism of users' sense of telepresence, copresence, and social presence in virtual environments

Abstract: We report on an experiment that examined the influence of anthropomorphism and perceived agency on presence, copresence, and social presence in a virtual environment. The experiment varied the level of anthropomorphism of the image of interactants: high anthropomorphism, low anthropomorphism, or no mage. Perceived agency was manipulated by telling the participants that the image was either an avatar controlled by a human, or an agent controlled by a computer. The results support the prediction that people respond socially to both human and computer-controlled entities, and that the existence of a virtual image increases telepresence. Participants interacting with the less-anthropomorphic image reported more copresence and social presence than those interacting with partners represented by either no mage at all or by a highly anthropomorphic image of the other, indicating that the more anthropomorphic images set up higher expectations that lead to reduced presence when these expectations were not met.

Toward a taxonomy of copresence

Abstract: This paper contributes to the presence literature by explicating the meanings and subtypes of copresence. Copresence is defined here as consisting of two dimensions: copresence as mode of being with others, and copresence as sense of being with others. Mode of copresence refers to the physical conditions that structure human interaction. Six such conditions are delineated. Sense of copresence, on the other hand, refers to the subjective experience of being with others that an individual acquires in interaction. The main argument of this paper is that mode of copresence affects sense of copresence, and knowledge of now the former affects the latter will benefit copresence design.

A survey of surgical simulation: applications, technology, and education

Abstract: Surgical simulation for medical education is increasingly perceived as a valuable addition to traditional teaching methods. Simulators provide a structured learning experience, permitting practice without danger to patients, and simulators facilitate the teaching of rare or unusual cases. Simulators can also be used to provide an objective assessment of skills. This paper is a survey of current surgical simulator systems. The components of a simulator are described, current research directions are discussed, and key research questions are identified.

Social inhibition in immersive virtual environments

Abstract: We assessed the utility of using immersive virtual environment (IVE) technology for social psychological research by attempting to replicate two classic social influence effects. Specifically, we sought to replicate the classic social facilitation/inhibition effects wherein individuals' performance on a task is affected by the presence of others. Within an IVE, participants mastered one of two tasks and subsequently performed the mastered or nonmastered task either alone or in the presence of a virtual human audience whom they were led to believe were either computer-controlled agents or human-controlled avatars. Those performing in the presence of avatars demonstrated classic social inhibition performance impairment effects relative to those performing alone or in the presence of agents. We discuss important elements involved in the experience of social influence within immersive virtual environments.

Presence equation: an investigation into cognitive factors underlying presence

Abstract: The relationship between presence and cognitive factors such as absorption, creative imagination, empathy, and willingness to experience presence was investigated. Presence was defined, operationalized, and measured using a questionnaire that we devised. Absorption and creative imagination were measured using questionnaires developed in the area of hypnosis, and empathy was assessed through an interpersonal reactivity index. Results indicated significant correlations between presence and each cognitive factor. They showed that persons who are highly fantasy prone, more empathic, more absorbed, more creative, or more willing to be transported to the virtual world experienced a greater sense of presence. Regression analysis led to a presence equation, which could be used to predict presence based on the investigated cognitive factors. Findings are congruent with user characteristics presented by the presence iterature and support the position that individual differences are important for the study of presence.

Media psychology "is not yet there": introducing theories on media entertainment to the presence debate

Abstract: Contemporary theoretical explications of presence experiences can be advanced and completed by integrating theoretical frameworks from media psychology. This article briefly presents concepts related to media entertainment that have been elaborated and/or applied by media psychologists and that exhibit considerable overlaps with the explication of presence. Specifically, the concept of involvement (Vorderer, 1992), affective disposition theory (Zillmann, 1996), simulation theory (Oatley, 1994), and the psychological theory of play (Oerter, 1999) are introduced. For each framework connection points to the theoretical conceptualization of presence are pointed out. The article illuminates new opportunities for interdisciplinary cooperation in advancing our understanding of presence.

Virtual laboratories: comparability of real and virtual environments for environmental psychology

Abstract: Virtual environments have the potential to become important new research tools in environment behavior research, They could even become the future (virtual) laboratories, if reactions of people to virtual environments are similar to those in real environments. The present study is an exploration of the comparability of research findings in real and virtual environments. In the study, 101 participants explored an identical space, either in reality or in a computer-simulated environment, Additionally, the presence of plants in the space was manipulated, resulting in a 2 (environment) × 2 (plants) between-subjects design. Employing a broad set of measurements, we found mixed results. Performances on size estimations and a cognitive mapping task were significantly better in the real environment. Factor analyses of bipolar adjectives indicated that, although four dimensions were similar for both environments, a fifth dimension of environmental assessment--termed arousal--was absent in the virtual environment. In addition, we found significant differences on the scores of four of the scales. However, no significant interactions appeared between environment and plants. Experience of and behavior in virtual environments have similarities to that in real environments, but there are important differences as well, We conclude that this is not only a necessary, but also a very interesting research subject for environmental psychology.

Psychophysical characterization and testbed validation of a wearable vibrotactile glove for telemanipulation

Abstract: This paper describes and evaluates a high-fidelity, low-cost haptic interface for teleoperation. The interface is a wearable vibrotactile glove containing miniature voice coils that provides continuous, proportional force information to the user's fingertips. In psychophysical experiments, correlated variations in the frequency and amplitude of the stimulators extended the user's perceptual response range compared to varying amplitude or frequency alone. In an adaptive, force-limited, pick-and-place manipulation task, the interface allowed users to control the grip forces more effectively than no feedback or binary feedback, which produced equivalent performance. A sorting experiment established that proportional tactile feedback enhances the user's ability to discriminate the relative properties of objects, such as weight. We conclude that correlated amplitude and frequency signals, simulating force in a remote environment, substantially improve teleoperation.

Reflections on real presence by a virtual person

Abstract: I have lived in San Francisco while working as a full-time virtual faculty member for Michigan State University for nearly six years. Unlike most humans, I spend a larger proportion of every day as a virtual person than as a physical person. This article is adapted from a keynote speech I delivered at the Fourth International Workshop on Presence in Philadelphia in May of 2001. I use a personal narrative style to explore issues and to question some of the research community's prevailing assumptions about presence.Lombard and Ditton's (1997) frequently cited conceptualization defines presence as a "perceptual illusion of nonmediation" that occurs "when a person fails to perceive or acknowledge the existence of a medium in his/her communication environment and responds as he/she would if the medium were not there." The underlying assumption is that, in the absence of technology, everyone experiences continuous presence at a constant intensity throughout their lives.Instead, this article suggests that presence is not a constant of everyday nonmediated experience. Careful consideration of unmediated (real) presence might help the conceptualization and study of mediated presence.

Real handball goalkeeper vs. virtual handball thrower

Abstract: Virtual reality offers new tools for human motion understanding. Several applications have been widely used in teleoperation, military training, driving and flying simulators, and so forth. We propose to test if virtual reality is a valid training tool for the game of handball. We focused on the duel between a handball goalkeeper and a thrower. To this end, we defined a pilot experiment divided into two steps: an experiment with real subjects and another one with virtual throwers. The throwers' motions were captured in order to animate their avatar in a reality center. In this paper, we focused on the evaluation of presence when a goalkeeper is confronting these avatars. To this end, we compared the goalkeeper's gestures in the real and in the virtual experiment to determine if virtual reality engendered the same movements for the same throw. Our results show that gestures did not differ between the real and virtual environment. As a consequence, we can say that the virtual environment offered enough realism to initiate natural gestures. Moreover, as in real games, we observed the goalkeeper's anticipation to allow us to use virtual reality in future work as a way to understand the goalkeeper and thrower interactions. The main originality of this work was to measure presence in a sporting application with new evaluation methods based on motion capture.

Constructing a Gazebo: supporting teamwork in a tightly coupled, distributed task in virtual reality

Abstract: Many tasks require teamwork. Team members may work concurrently, but there must be some occasions of coming together. Collaborative virtual environments (CVEs) allow distributed teams to come together across distance to share a task. Studies of CVE systems have tended to focus on the sense of presence or copresence with other people. They have avoided studying close interaction between users, such as the shared manipulation of objects, because CVEs suffer from inherent network delays and often have cumbersome user interfaces, Little is known about the effectiveness of collaboration in tasks requiring various forms of object sharing and, in particular, the concurrent manipulation of objects.This paper investigates the effectiveness of supporting teamwork among a geographically distributed group in a task that requires the shared manipulation of objects. To complete the task, users must share objects through concurrent manipulation of both the same and distinct attributes. The effectiveness of teamwork is measured in terms of time taken to achieve each step, as well as the impression of users. The effect of interface is examined by comparing various combinations of walk-in cubic immersive projection technology (IPT) displays and desktop devices.

DIVERSE: A Framework for Building Extensible and Reconfigurable Device Independent Virtual Environments | NIST

Abstract: We present DIVERSE, a highly modular collection of complimentary software packages designed to facilitate the creation of device independent virtual environments. DIVERSE is free/open source software, containing both end-user programs and C++ APIs (Application Programming Interfaces). DgiPf is the DIVERSE graphics interface to OpenGL Performer/sup TM/. A program using DgiPf can run on platforms ranging from fully immersive systems such as CAVEs/sup TM/ to generic desktop workstations without modification. We describe DgiPf's design and present a specific example of how it is being used to aid researchers.

Systematic usability evaluation and design issues for collaborative virtual environments

Abstract: This paper presents results of the longitudinal usability and network trials that took place throughout the COVEN (COllaborative Virtual ENvironments) Project. To address the lack of understanding about usability design and evaluation for collaborative virtual environments (CVEs), a deductive analysis was used to systematically identify areas of inquiry. We present a summary of the analysis and the resulting framework through which various complementary methods were utilized during our studies. The objective of these studies was to gain a better understanding about design, usability, and utility for CVEs in a multidisciplinary setting.During the studies, which span four years, we undertook longitudinal studies of user behavior and computational demands during network trials, usability inspections of each iteration of the project demonstrators, consumer evaluations to assess social acceptability and utility of our demonstrators, and continuous preparations of design guidelines for future developers of CVEs.In this paper, we discuss the need for such activities, give an overview of our development of methods and adaptation of existing methods, give a number of explanatory examples, and review the future requirements in this area.

Effects of handling real objects and self-avatar fidelity on cognitive task performance and sense of presence in virtual environments

Abstract: Immersive virtual environments (VEs) provide participants with computer-generated environments filled with virtual objects to assist in learning, training, and practicing dangerous and/or expensive tasks. But does having every object being virtual inhibit the interactivity and level of immersion? If participants spend most of their time and cognitive load on learning and adapting to interacting with virtual objects, does this reduce the effectiveness of the VE?We conducted a study that investigated how handling real objects and self-avatar visual fidelity affects performance and sense of presence on a spatial cognitive manual task. We compared participants' performance of a block arrangement task in both a real-space environment and several virtual and hybrid environments. The results showed that manipulating real objects in a VE brings task performance closer to that of real space, compared to manipulating virtual objects. There was no significant difference in reported sense of presence, regardless of the self-avatar's visual fidelity or the presence of real objects.

Fidelity metrics for virtual environment simulations based on spatial memory awareness states

Abstract: This paper describes a methodology based on human judgments of memory awareness states for assessing the simulation fidelity of a virtual environment (VE) in relation to its real scene counterpart. To demonstrate the distinction between task performance-basec approaches and additional human evaluation of cognitive awareness states, a photorealistic VE was created. Resulting scenes displayed on a head-mounted display (HMD) with or without head tracking and desktop monitor were then compared to the real-world task situation they represented, investigating spatial memory after exposure. Participants described how they completed their spatial recollections by selecting one of four choices of awareness states after retrieval in an initial test and a retention test a week after exposure so the environment. These reflected the level of visual mental imagery involved during retrieval, the familiarity of the recollection and also included guesses, even if informed. Experimental results revealed variations in the distribution of participants' awareness states across conditions while, in certain cases, task performance failed to reveal any. Experimental conditions that incorporated head tracking were not associated with visually induced recollections. Generally, simulation of task performance does not necessarily lead so simulation of the awareness states involved when completing a memory task. The general premise of this research focuses on how tasks are achieved, rather than only on what is achieved. The extent to which judgments of human memory recall, memory awareness states, and presence in the physical and VE are similar provides a fidelity metric of the simulation in question.

Six-degree-of-freedom haptic rendering using incremental and localized computations

Abstract: We present a novel six-degree-of-freedom haptic rendering algorithm using incremental and localized contact computations. It uses an incremental approach for contact and force computations and takes advantage of spatial and temporal coherence between successive frames. As part of a preprocess, we decompose the surface of each polyhedron into convex pieces and construct bounding volume hierarchies to perform fast proximity queries. Once the objects have intersected, we compute the penetration depth (PD) in the neighborhood of the contact between each pair of decomposed convex pieces using a new incremental algorithm. Moreover, we cluster different contacts based on their spatial proximity to speed up the force computation. We have implemented this algorithm and applied it to complex contact scenarios consisting of multiple contacts. We demonstrate its effectiveness on electronic prototyping of complex mechanical structures and virtual exploration of a digestive system.

VELVET: an adaptive hybrid architecture for very large virtual environments

Abstract: Collaborative virtual environment (CVE) concepts have been used in many systems in the past few years. Applications of such technology range from military combat simulations to various civilian commercial applications. The architectures available today provide support for a number of users, but they fail if too many users are together in a small "space" in the virtual world. This paper introduces VELVET, an adaptive hybrid architecture that allows a greater number of users to interact through a CVE. This is accomplished through an adaptive filtering scheme based on multicasting. VELVET also supports small groups of users, but its use in large environments shows the greatest potential, better handling local concentrations of activity than region-, cell-, or locale-based approaches. VELVET introduces a novel adaptive area of interest management that supports heterogeneity amongst the various participants. This allows users in a supercomputer with high-speed networking to successfully collaborate with others in not-so-powerful systems behind a slow dial-up connection.

Amplifying head movements with head-mounted displays

Abstract: The head-mounted display (HMD) is a popular form of virtual display due to its ability to immerse users visually in virtual environments (VEs). Unfortunately, the user's virtual experience is compromised by the narrow field of view (FOV) it affords, which is less than half that of normal human vision. This paper explores a solution to some of the problems caused by the narrow FOV by amplifying the head movement made by the user when wearing an HMD, so that the view direction changes by a greater amount in the virtual world than it does in the real world. Tests conducted on the technique show a significant improvement in performance on a visual search task, and questionnaire data indicate that the altered visual parameters that the user receives may be preferable to those in the baseline condition in which amplification of movement was not implemented. The tests also show that the user cannot interact normally with the VE if corresponding body movements are not amplified to the same degree as head movements, which may limit the implementation's versatility, Although not suitable for every application, the technique shows promise, and alterations to aspects of the implementation could extend its use in the future.

In search of presence: a systematic evaluation of evolving VLEs

Abstract: In an attempt to understand better the unique characteristics of an increasing popular, prevalent form of sense-engaging and interactive multimedia learning experience often called the "virtual learning environment" (VLE), this study systematically evaluates and analyzes the findings of seventeen original research studies in terms of technologies, teaching strategies, presence, and learning.This evaluation identifies potentially significant relationships among these variables in VLEs with both low- and high-level learning objectives, from memorization and repetition to analysis and synthesis. The findings suggest, first, that, when technologies and teaching strategies are presented through a one-way immersion of the senses, learners most often respond with experiences of spatial presence; when technologies and teaching strategies are socially interactive in format, learners most often respond with experiences of social presence. This evaluation, importantly, suggests that levels of spatial presence may correlate with the achievement of lower-level learning objectives, that levels of social presence may correlate with the achievement of higher-level learning objectives, and that levels of spatial and social presence together may correlate most strongly with the achievement of higher-level learning objectives. The evaluation, finally, identifies a need and establishes a course for the consideration of presence in future VLE design and research.

Virtual reality serves as a support technology in cardiopulmonary exercise testing

Abstract: The purpose of this study was to develop a virtual cycling system and examine the influence of virtual reality (VR) on test performance during clinical exercise testing. We aimed to compare the physiological responses of the cardiovascular and ventilatory systems during incremental exercise testing with or without VR and to measure VR effects on the ratings of perceived exertion (RPE) and cycling duration throughout the test.Twelve healthy senior citizens (ten men and two women) with a mean age of 74.5 ± 4.7 years participated in the study. The codes of behavior for this study included a maximum graded exercise tolerance test, a submaximal endurance VR exercise, and a submaximal endurance non-VR exercise, A friction-braked cycle ergometer was used co conduct the exercise tests. For the subject's movement speed to create an appropriate environment flow on the display screen the bike was connected to a personal computer. The cardiorespiratory and hemodynamic parameters were evaluated at both peak and submaximal exertion.The results show that the VR versus non-VR programs did not differ on submaximal and peak exercise responses during the cycling test. However, significant differences were observed between the mean values for cycling duration, distance, and energy consumption. The difference between RPE curves for VR and non-VR protocols revealed promising results within 45 min. of cycling (Breslow test, p = .06); however, no statistical significance was achieved at the test termination (log rank test, p = .17).In conclusion, this study found that the maintenance of endurance the increase in target intensity, and total energy consumption in exercise programs may be assisted by introducing VR technology. In addition, the activities taking place in virtual environments can be performed in complete safety.

Presence as experience: film informing ways of staying there

Abstract: Experience and the activities that provide it are associated with the virtual places where they were encountered, and this may instill in our imagination an illusion of an environment other than where an interactive mediated environment (a virtual environment, virtual reality, or computer game) resides (home, work, or on the move). Appropriate and/or stimulating experience may encourage users to continue, or become engaged in, pursing activities in a mediated environment. The term staying there is used to describe this situation of engagement. Conversely, if experience from use does not match up or deliver on expectations or purpose, or it is dull, boring, or uninteresting, then it may not hold user's attention and can potentially shift attention from the mediated to the real world. This paper describes the background work towards the development of a framework of experience with the aim of informing analysis and design of interactive mediated environments (IMEs) to induce/evoke stimulating experience in users and to encourage them in "staying there." informed from filmmaking, three levels of experience are explored: voyeuristic ("joy of seeing the new and the wonderful"), visceral (thrill of spectacle and attractions), and vicarious (transfer of emotion through another person, being, or object). With varying degrees of emphasis, story is experienced by spectators through one or a combination of these three to provide meaning. Drawing a parallel between developments in film and IMEs, situations, circumstances, features, and elements of IME design are identified that can induce/evoke these experiences in users. As well as informing analysis and design of experience of IMEs, this may provide an alternative way to reason about engagement and presence.

Objective metrics for the evaluation of simple surgical skills in real and virtual domains

Abstract: Surgical skills are traditionally assessed through subjective evaluation with experienced surgeons observing and rating trainee activity. However, this process can be expensive, particularly in terms of the time required of expert surgeons. Subjective assessment may also suffer from problems of intersubject variation in the application of evaluation criteria. Computer-based training, in particular systems combining virtual reality interfaces with haptic displays, offers a means of providing both automated and objective assessment of performance. In this paper we propose that, prior to the development of such systems, there is a need to determine measures that can adequately differentiate levels of performance. The paper therefore discusses the evaluation of surgical technique using objective metrics. Two main questions are addressed. How can surgical technique be assessed? What metrics prove useful in defining and modifying surgical skills and techniques?

Designing for presence and performance: the case of the virtual fish tank

Abstract: Although much research work has focused on identifying different factors that affect presence, it is still not clear how to effectively combine these results to create a content with high presence with respect to a given hardware set-up and limited computing resources This paper proposes a concept of level of presence (LOP) in which we attempt to select a set of presence elements and their levels to maximize their "contribution" toward the overall presence subject to system resources Such an optimization scheme would require a reasonable characterization of the computational costs and a sufficient knowledge of the relative and collective merits of various presence elements We made an attempt to apply the LOP concept to VR system design for a particular application, a virtual fish tank The purpose of this study is to assess the usefulness of the LOP concept and introduce science into content creation We selected two important presence elements--the field of view (FOV) and the simulation level of detail (SLOD)--and quantified their costs in terms of the required computation time Next, we ran a simple experiment to quantify the relative benefits of those two presence factors For this application, it was found that providing more lifelike simulation, for instance, incurred needlessly expensive computations compared to the amount of increased benefits Based on the result, the virtual fish tank was configured with the appropriate FOV and SLOD for maximum presence under different conditions, such as the preferred frame rate and total number of objects We discuss the merits of such a presence-driven VR system development approach

Precision of exocentric distance judgments in desktop and cube presentation

Abstract: Accuracy of space perception and distance estimation in virtual environments is an important precondition for the reliable use of virtual techniques in the design of products, workplaces, architecture, and production systems. The present study compares the accuracy of exocentric distance estimations that a static perceiver achieves with two virtual presentation techniques: a desktop and an immersive cube presentation. Estimation accuracy in a physical mock-up is used as a point of reference. Subjects estimated exocentric distances in detailed models of a workplace previously unknown to them. All distances to be judged were located in the subjects' personal space (less than 1.5 m from the subject).Major differences between the two virtual presentation modes are that stereo information is available in the cube but not in desktop environment, and that, in the cube, cnanges in perspective are achieved by actually moving inside the cube instead of using a mouse. Furthermore, the cube provides a wider absolute field of view than the desktop environment.The experiment showed advantages of the cube over desktop presentation when estimating exocentric distances in "personal space" from a static position. The magnitude of distance estimation errors was significantly higher in the desktop than in the cube environment. However, estimation errors tended to be overestimations in the cube presentation, whereas over- and underestimation occurred with equal frequency in the desktop environment.In the discussion it is argued that the higher estimation accuracy in the cube environment may mainly be due to the availability of stereoscopic depth cues. According to Cutting (1997), these cues are especially relevant for spatial perception in "personal space."

Levels of control during a collaborative carrying task

Abstract: Three experiments investigated the effect of implementing low-level aspects of motor control for a collaborative carrying task within a VE interface, leaving participants free to devote their cognitive resources to the higher-level components of the task. In the task, participants collaborated with an autonomous virtual human in an immersive virtual environment (VE) to carry an object along a predefined path. In experimental, participants took up to three times longer to perform the task with a conventional VE interface, in which they had to explicitly coordinate their hand and body movements, than with an interface that controlled the low-level tasks of grasping and holding onto the virtual object. Experiments 2 and 3 extended the study to include the task of carrying an object along a path that contained obstacles to movement. By allowing participants' virtual arms to stretch slightly, the interface software was able to take over some aspects of obstacle avoidance (another low-level task), and this led to further significant reductions in the time that participants took to perform the carrying task. Improvements in performance also occurred when participants used a tethered viewpoint to control their movements because they could see their immediate surroundings in the VEs. This latter finding demonstrates the superiority of a tethered view perspective to a conventional, human's-eye perspective for this type of task.

Movement behavior for soldier agents on a virtual battlefield

Abstract: We have developed a movement behavior model for soldier agents who populate a virtual battlefield environment. Whereas many simulations have addressed human movement behavior before, none of them has comprehensively addressed realistic military movement at individual and unit levels. To design an appropriate movement behavior model, we found it necessary to • elaborate all of the requirements on movement from the military tasks of interest, • define a behavior architecture that encompasses all required movement tasks, • select appropriate movement planning and control approaches in light of the requirements, and • implement the planning and control algorithms with novel enhancements to achieve satisfactory results.The breadth of requirements in this problem domain makes simple behavior architectures inadequate and prevents any single planning approach from easily accomplishing all tasks. In our behavior architecture, a hierarchy of tasks is distributed over unit leaders and unit members. For movement planning, we use an A* search algorithm on a hybrid search space comprising a two-dimensional regular grid and a topological map; the plan produced is a series of waypoints annotated with posture and speed changes. Individuals control movement with reactive steering behaviors. The result is a system that can realistically plan and execute a variety of unit and individual agent movement tasks on a virtual battlefield.

Being and time: judged presence and duration as a function of media form

Abstract: We briefly describe a novel immersive environment--the interactive tent--and an artistic production within it, the Illusion of Being. In this production, immersants experience a vivid cycle of the elements in a way that depends on their bodily movements. This elemental "story" has four versions in all, with each created to have differential effects on sense of presence and of subjective duration, according to a theoretical model. The model proposes three orthogonal dimensions of experience: focus, the level of abstraction: locus, real versus virtual; and sensus, the overall level of attention of the observer. An experiment, conducted to assess the effects of the different versions, is reported. The results confirmed the model's prediction that rated presence is relatively high when experienced media is of a form that elicits predominantly concrete (perceptual) processing, and relatively low when the emphasis is on more-abstract (conceptual) processing. But the concrete-abstract dimension had no direct effect on judged duration, contrary to our predictions. However, some evidence suggests that judged presence and estimated duration were positively correlated for media categorized as virtual, but not for content captured from the real world.