The Psychology of Virtual Presence: Research Ideas
January 24, 2002
NOTE: this is a set of research ideas that I developed a few years ago, but did not have a chance to follow-up.
If anyone is interested in conducting research like this, please contact me at (firstname.lastname@example.org)
A growing number of products are attempting to create a sense of presence where users feel that remote objects are actually nearby, or synthetically created objects actually exist. Creating a sense of presence is often a goal for training simulators and thrill rides as well as virtual reality (VR) systems, home theatres, IMAX films, HDTV, and video arcade games. Remote communications, such as those enabled by videoconferencing systems, also attempt to create a sense that distant users are physically present, or at least can be treated that way during conversations. Creating a sense of presence is felt to be important because it makes products appear more natural, immediate, direct, and real (Lombard & Ditton, 1997). This research project is a scientific examination of this sense of presence and the role it plays in creating satisfying and successful products and systems.
In discussions on the topic of presence, important terms have not always been used consistently. Since presence is a phenomenon that is subject to personal interpretation, developing a consistent language for discussing the topic is important. In this section, definitions are provided for the important concepts in presence research.
The term "presence" is defined as "the fact or condition of being present" or "something… felt or believed to be present" (Webster's New Collegiate Dictionary, 1981). Thus, "presence" may indicate a true condition when an object is actually present in the physical world (the first definition). The term "presence" may also connote a personal perception of the real world, embodied in a feeling or belief (the second definition). This perception may be wrong at times when a perception of presence occurs when an object is not present in the real world. This case we will call the "illusion of presence" (Heeter, 1992), and our interest is in how products can create the illusion of presence and use it for positive outcomes.
Like most perceptual illusions, the illusion of presence is not abnormal but instead is a function of the normal operations of our perceptual and social systems. For the illusion of presence, it is likely that the human perceptual system has evolved a safety mechanism for rapidly reacting to threats that assumes that all stimuli are real until further information is available. This may be a very valuable strategy at certain times (i.e., during periods of sleep or daydreaming), but a by-product is an illusion of presence where objects can appear to be present when they are not (Lombard & Ditton, 1997). By examining illusions in detail, we can often learn a great deal about the underlying perceptual processes.
A related term in this area of research is "telepresence", which can be defined as an illusion of presence that occurs over a distance that is mediated by telecommunications technologies. In telepresence, the mediating technology may become invisible to the users so that remote people or objects appear to be locally present, or at least can be treated that way during the course of communications. Creating telepresence is often an explicit goal of videoconferencing systems (e.g., Bocker & Muhlbach, 1993; Muhlbach, et al., 1995).
"Virtual presence" can be defined as an illusion of presence that is created by artificial devices, such as computer displays, headphones, etc. Virtual presence is often associated with "Virtual Reality" (VR) or "Virtual Environment" (VE) systems, where computers are used to generate objects and environments that are presented to users through a number of senses (i.e., vision, hearing, touch). (Since the term "virtual reality" is an oxymoron, the more informative term "virtual environment" (VE) will be used here.) In many virtual environment systems, immersive input devices (e.g., vivid head-mounted displays, stereophonic headphones) are used to stimulate the senses and people experience a compelling illusion of being somewhere they are not (Slater & Wilbur, 1997). Virtual presence can be considered as a special case of telepresence where the remote environment is artificially created (Schloerb, 1995). This phenomenon of virtual presence is the topic of interest for this research project.
It should be noted that an illusion of presence is not new to computer systems and immersive virtual environments. "Literary presence" can be defined as an illusion of presence that is created by story telling. This illusion is a common artistic goal for such traditional communication technologies as books, theatre, television, and film (Lombard & Ditton, 1997). Through the written word, the spoken voice, and images on film, people can be made to believe, at least at a shallow level, that they are somewhere they are not, or in the presence of people and objects that do not actually exist. The strength of the illusion is related to a willingness in the audience to suspend disbelief. New computer technologies have simply made it possible to create more compelling illusions, and forced storytellers to be more conscious of the illusions of presence they can create. A good example of this is the illusion of presence that can be created by text-based virtual environments (e.g., MUDs and MOOs; Roberts et al., 1996; Towell & Towell, 1997).
"Psychology" is the science of behaviour and mental processes. It is the study of how and why people (and other organisms) do what they do (Gleitman, 1986). Within Psychology, there is a sub-field of "human-computer interaction" (HCI) that is concerned with the behaviour and mental processes involved when people interact with and through computers (and technology in general). HCI research can be motivated by discovery, where researchers attempt to determine the important phenomena and principles involved when humans and computers interact. HCI can also be a science of design, where researchers attempt to support the interaction of people and technology through the development of new technologies (Carroll, 1997). In practice, HCI research tends to be a blend of discovery and development.
With these definitions in place, we can now define the topic of this research project: "The Psychology of Virtual Presence". This research is an attempt to understand the mental processes associated with the illusion of artificial objects being present when they are not, the behaviour this illusion can cause, and the implications that it has for the design of technology.
Importance to Industry
We are seeing increasing interest in the use of virtual environment technologies for a number of applications. Virtual environment systems are being developed for a variety of training situations, including automobile driving, pilot training, equipment maintenance, medical procedures, military combat tactics, astronauts, and fire-fighters (to mention only a few). VE systems are also being used for numerous design tasks, such as architecture and automobile designs. Virtual environment technologies are finding their way into games and entertainment systems, where we are seeing interactive 3D graphics and low-cost head-mounted displays. More recently, VE systems have proven to be a successful tool for the treatment of phobias. It is clear that interest in virtual environments will continue to grow for the foreseeable future.
One research area that is receiving a lot of attention lately is distributed virtual environments (DVEs), where people work together in a virtual environment even if they are physically separated by thousands of miles. DVEs might be used to collaborate on design projects, so architects can "walk through" virtual designs together regardless of where they are located physically. DVEs might also be valuable for distance education, where students and teachers could interact with each other and synthetic objects in the virtual environment. The military has a keen interest in developing distributed simulations where multiple users could be trained in large, worldwide battle simulations (Waters & Barrus, 1997).
For all of these applications, we need a better understanding of what presence is, what causes it, and what are the positive and negative effects of using VE technologies (Lombard & Ditton, 1997). There is some suggestion that an illusion of presence is valuable because it increases motivation and leads to better learning and a more engaging experience (but see Ellis, 1996, for a contrary opinion). Systematic research on these effects has been lacking, however.
An understanding of presence is also needed to support the design of new VE systems. We need to know the role an illusion of presence plays in these systems, and we must determine the factors that are most important for creating an illusion of presence. For example, we need to know how important such factors as visual display fidelity, response time, and interactivity are for developing VE systems.
There are also a number of important research issues for DVE systems related to the communications networks used to connect remote users. What data bandwidth is required to maintain an illusion of presence? How fast must the systems communicate, and what level of interactivity is required?
Key Research Issues
A review of the literature has suggested a number of important issues for research on virtual presence, and a clear starting point for new research. (Interested readers should see Biocca & Levy, 1995, and Lombard & Ditton, 1997, for recent reviews.)
Causes, Control, and Manipulation of Virtual Presence
When designing VE systems, a developer needs to know how to induce an illusion of presence and how this illusion can be controlled. For example, some research has suggested that the most important cause of the illusion is the number of senses receiving input. Systems that present data to more of the visual, auditory, tactile, and kinetic senses will produce more of an illusion than systems that involve fewer of the senses. Virtual technologies that involve and saturate more of the senses are said to be more "immersive" than other systems. Research has also suggested that it is the consistency of the data across the senses that is most important, so an illusion of presence occurs when the visual, auditory, and other channels are all working together.
Other research has examined the characteristics of the visual display used in virtual environments. Factors that appear to be important include the image size, usually expressed as the portion of the visual field involved by the display. The image quality is also thought to be important, and this includes using stereoscopic technologies to present 3D images (e.g., Barfield & Weghorst, 1993; Hendrix & Barfield, 1996a; Welch et al., 1996). The rendering techniques are also important, with the use of close-ups, point-of-view angles (e.g., automobile bumper cameras), and subjective viewpoints all considered important for creating the illusion of presence. The obtrusiveness of the technology is also thought to be important, with a stronger illusion being possible if the medium does not draw attention (e.g., the edges of a visual display are not visible).
The aural channel has also received attention. The quality of the audio signal and the dimensionality induced by multiple channels are thought to be important in this research (e.g., Hendrix & Barfield, 1996b). Other senses have also been examined, most notably the kinetic sense involved in detecting body movements. This sense is commonly exploited in simulator rides that use tilting and bumping movements to create the illusion of forward motion. The tactile sense has also been used in systems that present force feedback and textures to the users. Some VE entertainment systems have even attempted to involve the sense of smell, even if it is just using scratch-and-sniff cards in movie theatres.
Another important factor in creating an illusion of presence is the amount of interactivity between the user and the virtual environment. The illusion is said to be stronger when the user has multiple methods to enter input, is able to control the environment and manipulate objects in a natural fashion (e.g., grasping), and receives rapid responses and feedback (e.g., Welch et al., 1996; Zeltzer, 1992).
There are also a number of social factors that are thought to be important for creating an illusion of presence. Environments are said to create more presence if there are a number of other people involved, if the interactions appear to be "live", and if the characters and stories are realistic.
Finally, user characteristics are also important. A willingness to suspend disbelief may be an important user characteristic when attempting to induce an illusion of presence. In addition, users' prior experience and level of expertise with the technology may be important, with more experienced users being less likely to experience an illusion of presence. There has also been some speculation that personality types and cognitive styles are important for determining personal reactions to virtual environments.
In all of these cases, there has been an abundance of discussion of the causes of presence, but very little systematic research. Few studies have carefully manipulated these variables and measured the effects on users.
The Effects of Virtual Presence
Another important area of research is the effect of virtual presence. What are the positive and negative consequences of creating an illusion of presence, and what does this mean for system design? Are all the effects of virtual environments positive, or can it be too intense for some applications and users?
There can be a number of physiological effects of experiencing virtual environments. Some researchers have suggested that an illusion of presence creates higher levels of arousal. There have also been demonstrations of various automatic responses to the virtual stimuli, such as ducking when looming objects are presented. The most notable physiological effects, however, are "vection", an illusion of self-motion, and sickness (Prothero et al., 1995). "Simulator sickness" is a common occurrence that appears to be related to a mismatch of sensory inputs that occurs with some virtual environments. One simplistic theory suggests that simulator sickness is caused by a mismatch of the kinetic and visual senses. When the motion and visual sensations do not match the body assumes that it has been poisoned, since poisons produce similar symptoms, and takes the most appropriate action (vomiting). This suggests that high-quality systems that ensure a good correlation between the kinetic and visual senses should be less prone to sickness problems. Simulator sickness is a serious problem that must be solved before immersive technologies can be widely adopted.
There are also psychological effects of virtual environments. VEs are said to produce more enjoyment and involvement than other media types. Material viewed using virtual technology is supposed to be more memorable and more persuasive (Kim & Biocca, 1997). In addition, working in virtual environments is thought to lead to better task performance, and better skills training. A psychological effect of particular interest is desensitisation to the stimuli experienced in a virtual environment. This is being exploited in research on the treatment of phobias, where people are better able to deal with the phobic stimuli (e.g., snakes or spiders) after they are experienced in an immersive virtual environment.
Measurement of Virtual Presence
The most important research issue is the measurement of virtual presence. How can we measure the illusion of presence in systematic and quantifiable ways? Without reliable, quantitative measures, it is impossible to answer the important questions in this field of research (Prothero et al., 1995; Schloerb, 1995).
The most common approach to measuring the illusion of presence is the problematic method of self-report questionnaires. Users who experience virtual environments are often asked to rate their agreement with such statements as:
The VE came to me and created a new world for me.
I felt I was in the world the VE created.
I forgot that I was in the middle of an experiment.
My body was in the room, but my mind was inside the world created by the technology.
The virtual world was more real or present for me compared to the "real world." (adapted from Kim & Biocca, 1997)
Although such questionnaires have been useful for developing the concept of presence, self-report measures have a number of problems. Users may use different meanings for the terms in the questions, resulting in different ratings for equivalent experiences. It is also not clear what dimensions of experience should be addressed in the questions. Kim and Biocca (1997) propose that there are two dimensions of presence that must be covered: a departure from the real world and an arrival in a virtual world. Sheridan (1996) suggests that three orthogonal dimensions are important for the illusion of presence: the information content of the stimulus (e.g., "The virtual image is compelling. Difficult to discriminate the virtual from the real based on given image."), the ability to modify the viewpoint in the VE (e.g., "Viewpoint with respect to the virtual environment can be changed easily…"), and the ability to modify and manipulate the VE (e.g., "Able to modify environment freely as easily as one would with bare hands or tools in a real environment."). Thus, it is not clear what self-report questionnaires should be asking about.
Given the inherent problems with subjective reports, some researchers have sought more objective measures of presence. Measuring the physiological effects of virtual environments is a likely alternative. One could measure changes in pupil size, skin conductance, blood pressure, and heart rate while users experience various VEs and attempt to correlate the features of the stimuli with the physical responses (Barfield & Weghorst, 1993). Strickland and Chartier (1997) went so far as to measure changes in EEG patterns during exposure to real and virtual environments and found systematic differences in brain activity. Held and Durlach (1991) suggest measuring the startle responses (e.g., blinking or ducking) to unexpected or looming stimuli, since this should indicate the extent that users are interpreting the environment as real. Unfortunately, it is not clear if such physical measures correlate with the illusion of presence experienced by users of virtual environments. Sheridan (1992) has argued that virtual presence is a subjective sensation that does not correspond with physiological definitions and measurements (much like mental workload), but there is little evidence on this issue.
Sheridan (1992, 1996) has suggested a psychophysical approach to measuring presence that may be interesting to pursue. The users' task would be to discriminate, using standard psychophysical techniques, between real and virtual environments. Given the poor quality of today's virtual environments, this discrimination will be easy. However, if perceptual "noise", created by filters or transformations, is added to the stimuli (both real and virtual) the discrimination will become harder and harder, until eventually the real and virtual environments are no longer distinguishable. The measure of presence becomes the amount of noise that is needed to make the real and virtual environments indistinguishable. Higher levels of virtual presence would be indicated by less noise required. The types of "noise" that could be manipulated in such experiments include resolution, frame rate, and colour for visual stimuli, and others could be developed for the other sensory modalities.
Another approach to developing objective measures of presence is being pursued in the Human Interface Technology (HIT) Laboratory at the University of Washington, one of the leading centres for virtual environment research. Similar to the psychophysical techniques proposed by Sheridan, the HIT lab is comparing real and virtual stimuli directly (Prothero et al., 1995). Real and virtual stimuli are presented at the same time and arranged in conflict. Presence is indicated when the virtual stimuli dominate over the real stimuli. For example, in one experimental procedure, subjects are placed in a chair perched on a rotating platform and the chair is oscillated back and forth with some frequency (much like the motion of a washing machine agitator). At the same time, the subjects are immersed in a virtual environment using a stereoscopic 3D, head-mounted display. The visual display also oscillates in a similar manner to the real environment. The subjects' task is to adjust the visual display to minimise any perception of motion (vection). Presence is indicated when the visual display is able to dominate and nullify the sensations created by the real motion. The results of such experiments have not been published, but this looks like a promising approach to developing objective measures of presence.
Researchers at the HIT Lab have another interesting approach to the measurement problem. Borrowing on research in human memory, it is proposed that presence can be measured by the amount of confusion between memories of real and virtual events (see Hoffman et al., 1994; Hullfish, 1995). A "source monitoring" paradigm is used where subjects are asked to remember the source of certain memories. In the classic memory research it was shown that under certain conditions people could have difficulty distinguishing between real and imagined events (e.g., Johnson et al., 1981). For example, people can fail to remember whether an experimenter read a word to them or they generated the word themselves from some semantic cues. The theoretical explanation is that there are a number of memory characteristics (or qualities) associated with the memory for events, specifically sensory, contextual, semantic, emotional and operational characteristics (Johnson et al., 1993). Memories from different sources have different memory characteristics. For example, memories from viewing a movie would have different visual and contextual characteristics than memories from real events. Normally, the different memory characteristics make it easy to identify the source of memories, but source confusions can occur when there is high similarity between the memory characteristics.
Since virtual presence is defined as the illusion of something being physically present when it is not, it follows that confusions between memories for actual and virtual events can provide a measure of presence. This was demonstrated in research done by Keith Hullfish for an Engineering MSc thesis at the HIT Lab. Hullfish (1996) conducted an experiment where people were asked to memorise spatial displays of objects presented in a pattern (i.e., a collection of boxes on the floor). The objects were presented in three environments: a real environment that included actual boxes arranged on the floor of a room, a virtual environment that presented the boxes in a stereoscopic head-mounted display, and an imagined environment where subjects were instructed to imagine the boxes arranged in the room. The dependent variable was the memory for the source of the displays during a later recognition test that included new patterns not seen in any of the display environments.
Hullfish found that people did confuse the memories for real and virtual displays. On 34% of the questions, people remembered the virtual patterns as being real. In fact, people only remembered the virtual displays as being virtual 28% of the time. In addition, the people in this study were more confident of their memories when they remembered the virtual displays as being real than when they correctly remembered them as virtual. These findings suggest that memories for real and virtual events can share similar memory characteristics, and this may be a very useful measure of virtual presence. Presence would be indicated by the amount of memory confusions between real and virtual events.
The research that I have planned will address the issue of the measurement of virtual presence. The overall goal is to develop an understanding of the psychology of virtual presence. This will be done by examining some approaches to the measurement of virtual presence and conducting a systematic examination of the factors that contribute to an illusion of presence. Another desired outcome is findings that will be useful when making design decisions for virtual environment technologies.
My initial experimentation will be based on the work done at the HIT Lab on source memory for virtual events. I will use the source monitoring paradigm to determine if there are differences in the memories for virtual events that are manipulated in ways thought to be important for creating an illusion of presence. For example, the visual fidelity of virtual displays will be modified and the effects on source monitoring errors will be examined. It is hypothesised that higher quality displays will lead to more of an illusion of presence, and more confusion with memories for real events. I also plan to evaluate the quantitative relationship between environment manipulations and the resulting memory variables.
In future studies it may be possible to adopt some of the ideas proposed by Sheridan and manipulate the noise of the real and virtual displays until they are indistinguishable in later memory tests. The amount of noise that is needed to make the memories indistinguishable would provide a measure of presence created by the virtual environment.
I have discussed this research with Hunter Hoffman, one of the lead researchers on virtual presence at the HIT Lab. His reactions were: "Great research program you have in mind. Please keep me posted on developments. …the area is almost completely unexplored."
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Appendix: A Possible First Experiment
If there is a lack of virtual environment equipment, the first experiments can be rather simple. For example, chess game displays could be used for the experimental stimuli. Positions consisting of six pawns, appearing one-at-a-time under user control and arranged in a geometric pattern, could be used for the memory tests. Subjects would be instructed to memorise the patterns for a later recognition test. The independent variable would be type of environment used for the displays, and this would include four conditions:
real: a real chessboard and real pawns
video: a video recording of a chessboard and pawns shown on a large-screen television set
VRML: a chessboard and pawns rendered in the Virtual Reality Mark-up Language (VRML) and displayed on a computer screen. Users would be encouraged to use the VRML viewer program to control their viewpoint during study. (Other experiments could also include a 3D VRML condition using LCD shutter glasses to produce a 3D experience.)
computer game: a chessboard and pawns displayed by a computer program that uses a perspective view (i.e., from a player's viewpoint behind one side of the board)
Subjects would study displays under the four conditions on different trials. The memory test would use a simple 2D paper display of chess positions that showed an overhead board view. These test displays would be very different from any of the study conditions. The subjects' task during the memory test would be to discriminate between old (studied) board patterns and new patterns not seen during the study phase. The subjects would indicate whether each test display was seen in a "real", "video", "game", or "VRML" environment, or not seen before. Subjects would also be asked to rate their confidence in their memory judgements. Finally, in order to be complete the subjects will also be asked for self-reports about the nature of any illusion of presence created in the various environments. For this measurement, I will use some of the questionnaire items that have been used in other presence research.
The experimental hypotheses are:
· subjects will be fairly accurate in remembering old versus new displays
· it will be difficult for subjects to remember the source of the displays
· subjects will often confuse real and virtual displays
· the amount of confusion between real and virtual displays will vary depending on the quality of the virtual environment, perhaps in the order of "video", "VRML" and "game".
· confidence ratings will also reflect the quality of the virtual environments
· the subjective reports of an illusion of presence will be correlated with the amount of memory confusions