Your task: Read the summary of six conceptualizations of presence below (taken from Lombard and Ditton, 1997, and bring to class six examples from your own life that best demonstrate these conceptualizations in your opinion. For example, if you feel that talking to someone on a cell phone is an excellent example of social richness (conceptualization 1), write that down and be prepared to argue why you think so. Do this for each of the six conceptualizations (for number 3, it's enough to pick one sub-concept).

At the Heart of It All: The Concept of Presence

Matthew Lombard Theresa Ditton

Department of Broadcasting, Telecommunications, & Mass Media Temple University

  Table of Contents

• Abstract
• Introduction
• Concept Explication

o Conceptualizations in the Literature

            o Presence Explicated 
      * Causes and Effects of Presence
            o Causes of Presence as Invisible Medium
            o Causes of Presence as Transformed Medium
            o The Effects of Presence 
      * Future Presence Research
      * References
      * About the Authors 

  Abstract

  A number of emerging technologies including virtual reality, simulation rides, video conferencing, home theater, and high definition television are designed to provide media users with an illusion that a mediated experience is not mediated, a perception defined here as presence. Traditional media such as the telephone, radio, television, film, and many others offer a lesser degree of presence as well. This article examines the key concept of presence. It begins by noting practical and theoretical reasons for studying this concept. Six conceptualizations of presence found in a diverse set of literatures are identified and a detailed explication of the concept that incorporates these conceptualizations is presented. Existing research and speculation about the factors that encourage or discourage a sense of presence in media users as well as the physiological and psychological effects of presence are then outlined. Finally, suggestions concerning future systematic research about presence are presented.

  Introduction

  Virtual reality. Simulation rides. Home theater. 3-D IMAX films. State-of-the-art video conferencing. Computers that "talk." Although these emerging technologies are different in a number of ways, each of them (and many others) is designed to give the user a type of mediated experience that has never been possible before: one that seems truly "natural," "immediate," "direct," and "real," a mediated experience that seems very much like it is not mediated; a mediated experience that creates for the user a strong sense of presence. Meanwhile, traditional media including the telephone, radio, film, and television continue to offer us a lesser sense of presence as well. This paper is about the concept of presence: what it is, what is known about how it is generated and the effects it has on media users, and how it might be studied.

  Why examine the concept of presence? There are compelling practical and theoretical reasons. An enhanced sense of presence is central to the use, and therefore the usefulness and profitability, of the new technologies mentioned above and others such as the video telephone, high definition television (HDTV), home and arcade video games, the World Wide Web (WWW), and more. These technologies either are now changing or are expected soon to change many of the ways we work, play, and live. In the business world video conferencing has already begun to replace physical travel [(Muhlbach, Bocker, & Prussog, 1995)]. Related systems are used in telemedicine [(Crump & Pfiel, 1995; Hamit, 1995)] and telepsychiatry [(Abkarian, King, & Krappes, 1987; Dongier, Tempier, Lalinec-Michaud, & Meunier, 1986; Jerome, 1986)], in distance learning [(Chu & Schramm, 1967; Hackman & Walker, 1990)], and for legal testimony from remote locations [(Miller, 1991)]. Virtual reality may have begun with military training and flight simulators [(Karr, Reece, & Franceschini, 1997; Rheingold, 1991)], but it is now or soon will be used for everything from arcade games [(Cook, 1992; Martin, 1997; Robertson, 1994)] to architectural and interior design [Yan & Ouhyoung, 1994)] to new kinds of exercise equipment (e.g., the VRbike [(Tectrix, 1995)]), to virtual sex [(teledildonics (Harvey, 1995))] to underwater exploration [(Stoker, Barch, Hine, & Barry, 1995)] to the training and assessment of surgical skills [(Ota, Loftin, Saito, Lea, & Keller, 1995)] and much more [(see "Information Group," 1997)]. Developing technologies in cinematography and film presentation have transformed the movies, providing us with life-like encounters with "Jurassic Park" dinosaurs, extraterrestrial "Aliens," and terrifying "Twisters" (the film "brings screen fiction unnervingly close to virtual reality" [(Ryan, 1996)]). Simulator rides (or "motion-based movies") add hydraulic movement to sequences that typically feature rapid-point-of-view movement, so "viewers" can take a Sub Oceanic Shuttle from San Francisco to Tokyo [("Take undersea tube," 1992)] or move through the environment of a music video [(Moon, 1993)] [(see Mahoney, 1996)]. Future generations of human-computer interfaces, with "intelligent agents" that have their own personalities and follow users' bidding, will surely further transform our use of the modern computer [(see Coughlin, 1996)]. But despite what may be the beginning of a new trend in which companies add social scientists and other "interaction specialists" to their design teams [(Aldersey-Williams, 1996)], most design decisions concerning all of these technologies are made by trial and error, lore, and "seat of the pants" exploration [(see Huston-Stein & Wright, 1979)]. A better understanding of what presence is, what encourages and discourages it in users, and its effects, should save valuable time and money and improve the end-product in the design of new and the redesign of current media technologies.

  On the theoretical side, scholars in communication, psychology, and other fields want to better understand psychological and physiological processes as they occur in nonmediated settings; how humans organize and interpret information in their environment, store and retrieve memories, make decisions, etc. To accomplish this, researchers often use mediated stimuli as a substitute for the nonmediated stimuli of interest (for convenience as well as control) and assume that their findings will apply in both contexts. A few of many examples that could be cited are studies of person perception [(Ekman, 1982; Feshbach & Cohen, 1988; Kleck & Mendolia, 1990; Provine, 1989)], how people estimated time to collision in auto accidents [(Hoffmann & Mortimer, 1994; McLeod & Ross, 1983)], the causes and effects of motion sickness [(Alexander & Barrett, 1975; Parker, 1964, 1971)], and the treatment of phobias [(McNally, 1987)]. Our current understanding of these processes is based on studies in which it has been assumed that mediated (i.e., presence-inducing) stimuli are exactly the same as nonmediated stimuli; if that assumption is wrong, we need to know (work by [Gale, Golledge, Pellegrino, and Doherty (1990)] suggests it may be wrong, at least in some learning contexts). So a better understanding of presence will allow us to refine and improve our psychological theories.

  Media scholars are interested in particular in how people are influenced by media presentations; an understanding of presence can enhance our theories here too. For example, [Shapiro and Lang (1991)] used a model of memory developed by [Johnson (1983)] to explain how people incorporate information from television into their judgments about the "real" world. They suggest that mediated experiences that closely mimic nonmediated ones cause difficulties for the reality-monitoring process so that when memories are retrieved, mediated and nonmediated experiences are confused. [Ditton (1997)] found tentative empirical support for this idea. Media scholars have begun to consider the role of presence in theories concerning the negative impact of violent portrayals, the positive impact of prosocial portrayals, the perceived credibility of news and information, the persuasiveness of advertising, and more.

  Beyond these reasons for examining presence, the fact that there is so much intense popular as well as academic interest in technology that creates a sense of presence beckons study. Why do we want these experiences that (at least in some sense) aren't "real"? What does presence offer us? Aside from its practical uses, what needs does it fulfill? How do these gratifications compare to those offered by the other media and nonmedia activities?

  Despite the centrality and importance of presence, it has not yet been carefully explicated, operationalized, or studied. The work that has been done is fragmentary and unsystematic, in part because the people interested in presence come from many different academic fields (including communication, psychology, cognitive science, computer science, engineering, philosophy, and the arts). Further, research conducted for or by private industry and government has typically remained proprietary. This article provides a unifying explication of the presence concept and brings together much of what is known or has been suggested about presence in the hope that it can serve as a starting point for systematic research and theory on this topic.

  In the remainder of this paper we (a) review several conceptualizations of presence in the literature and provide a unifying explication of the concept, (b) review some of what is known about the causes and effects of presence, and (c) recommend attributes of a program of research concerning this concept.

  Concept Explication

  Conceptualizations in the Literature

  As suggested above, a diverse group of people are interested in presence, how to create it, how to use it effectively, and how it mediates or generates a variety of responses. A review of several relevant literatures finds six interrelated but distinct conceptualizations of presence. Each of these conceptualizations, and where possible corresponding operational definitions, is presented here; this is followed by a detailed explication that encompasses all six conceptualizations.

  1. Presence as social richness

  To some scholars, primarily those who study communication in organizations, presence is the extent to which a medium is perceived as sociable, warm, sensitive, personal or intimate when it is used to interact with other people. Social presence theory [(Short, Williams, & Christie, 1976)] and media richness theory [(Rice, 1992)] were developed to better match communication media and organizational tasks to maximize efficiency and satisfaction. This is necessary because communication media are said to differ in the extent to which they "(a) can overcome various communication constraints of time, location permanence, distribution, and distance, (b) transmit the social, symbolic, and nonverbal cues of human communication; and (c) convey equivocal information" [(Rice, 1992, p. 452)].

  To measure social presence subjects perform various tasks with different media and evaluate each medium via a series of bipolar, seven-point semantic differential items including impersonal-personal, unsociable-sociable, insensitive-sensitive, and cold-warm [(Perse, Buton, Kovner, Lears, & Sen, 1992; Short, Williams, & Christie, 1976)]. The social presence ranking thus depends on the interaction of the medium and the task at hand and is based on the subjective judgment of the user. Media richness or information richness is measured less subjectively by examining a medium's "capacity for immediate feedback, the number of senses involved, personalization and language variety" [(Rice, 1992, p. 4)].

  Presence as social richness is related to two important concepts originally applied to nonmediated interpersonal communication: intimacy and immediacy. [Argyle and Dean (1965)] suggested that interactants vary physical proximity, eye-contact, intimacy of conversation topic, amount of smiling, and other behaviors to establish an equilibrium between conflicting approach and avoidance forces and thereby optimize an overall level of intimacy. Other scholars have expanded the list of intimacy behaviors to include posture and arm position, trunk and body orientation, gestures, facial expressions, body relaxation, touching, laughter, speech duration, voice quality, laughter, olfactory cues, and others [(Cappella, 1981; Hall, 1966; Mehrabian, 1969; Patterson, 1973)]. A medium high in presence as social richness allows interactants to adjust more of these variables and therefore more precisely adjust the overall level of intimacy.

  [Weiner and Mehrabian (1968)] outlined how choices of language can help create a sense of psychological closeness or immediacy. Others have suggested that intimacy behaviors [(e.g., Hackman & Walker, 1990)] and even the choice of a medium for interaction [(e.g., Heilbronn & Libby, 1973)] also influence this sense of immediacy. Although language and therefore immediacy can be varied within any medium that can transmit language, it seems logical to expect immediacy and presence as social richness to be correlated [(see Short, Williams, & Christie, 1976)].

  2. Presence as realism

  A second conceptualization of presence concerns the degree to which a medium can produce seemingly accurate representations of objects, events, and people -- representations that look, sound, and/or feel like the "real" thing. This conceptualization is typically used by human factors engineers to assess consumers' responses to variations in the characteristics of a medium. For example, in a study of television, [Hatada, Sakata, and Kusaka (1980)] manipulated viewing angle, display area, viewing distance, and other variables and then asked subjects to report their subjective evaluation of the "sensation of reality" they experienced. [Neuman (1990)] varied the resolution and screen size of high definition television systems and measured viewers' evaluation of a "sensation of realism effect." Heeter (1995) asked users of consumer virtual reality entertainment systems, "How real did the overall experience feel?" This conceptualization of presence is often used in a vague manner that fails to distinguish between two key types of "realism," which are here termed "social realism" and "perceptual realism." Social realism is the extent to which a media portrayal is plausible or "true to life" in that it reflects events that do or could occur in the nonmediated world (this is analogous to what [Potter (1988)] labels the semantic component of the "magic window" dimension of perceived reality). While presence as realism may include this type of social realism it also includes a perceptual element that is separate: a scene from a science fiction program may be low in social realism but high in perceptual realism because although the events portrayed are unlikely, the objects and people in the program look and sound as one would expect if they did in fact exist. On the other hand, the people and events in an animated presentation may be high in social realism but because they are not "photorealistic," they are low in perceptual realism.

  3. Presence as transportation

  Another conceptual definition of presence involves the idea of transportation. Three distinct types of transportation can be identified: "You are there," in which the user is transported to another place; "It is here," in which another place and the objects within it are transported to the user; and "We are together," in which two (or more) communicators are transported together to a place that they share.

    "You are There"

  This is perhaps the oldest version of presence. The oral tradition of early humans involved the telling of tales that transported each generation of listeners to a different time and place where the events occurred [(Biocca & Levy, 1995)]. Written narrative can have the same effect [(Gerrig, 1993; Radway, 1991)]. Recent AT&T advertisements told us that the telephone was "the next best thing to being there." Borrowing from the [1976 Jerzy Kozinski novel] and 1979 film, [Reeves (1991)] used the term "Being There" to describe how viewers experience the environment they encounter on television. Again with regard to television, [Kim (1996)] defines presence as a "feeling of being a part of the phenomenal environment created by television and not being a part of the physical environment surrounding the viewer and the television set" (p. 27). (The phrase often spoken by television hosts following a commercial break, "Welcome back," is consistent with the idea that viewers are "transported" during viewing.) The "you are there" concept is often used in discussions of virtual reality, which takes users to a virtual environment and leads to the "suspension of dis-belief that they are in a world other than where their real bodies are located" [(Slater & Usoh, 1993, p. 222)]. [Sheridan (1992)] discusses teleoperation (human manipulation of elements of a remote environment) and, following [Minsky (1980)], defines telepresence as "feeling like you are actually 'there' at the remote site of operation," while virtual presence is "feeling like you are present in the environment generated by the computer" (p. 120). (See also [Rheingold, 1991], who calls telepresence a "form of out-of-the-body experience" (p. 256), and [(Biocca & Levy, 1995; Heeter, 1992; Held & Durlach 1992; and Steuer, 1995)] for similar definitions). The concept of transporting users to remote physical places can also be found in "virtual tours" of art exhibits, museums, and tourist destinations on the world wide web [(WWW Virtual Tours, 1997)].

  A number of closed-ended questionnaire items have been used to measure this type of presence. After watching television, subjects in a study by [Kim (1996)] were asked to report how often they had had the following perceptions: "I felt I was in the world the television created," "the television-generated world seemed to me to be more like 'somewhere that I visited' rather than 'something that I saw'," and "my body was in this room, but my mind was inside the world created by the television." Following [Gerrig (1993)], Kim tentatively identified two factors that emerged in subject responses as "departure" (from the nonmediated environment) and "arrival" (in the mediated environment). In another study of responses to television, [Ditton (1997)] asked subjects, "How much of a sense of participation in the scene did you feel?" and "How much of a sense of involvement in the scene did you feel?". [Slater and Usoh (1993)] asked virtual reality users, "To what extent did you experience a sense of being 'really there' inside the virtual environment?" (p. 227). In a study of consumer responses to a second person virtual reality entertainment system (one in which users stay in front of a camera and watch a television monitor that displays images of themselves acting inside a virtual environment), [Heeter (1995)] asked subjects, "Which felt like the real you -- the being on the screen or the one the camera was pointed at?" All of these measures assess the degree to which media users are transported into a distinct mediated environment.

    "It is Here"

  Instead of transporting the user to a different place, a sense of presence may bring the objects and people from another place to the media user's environment. According to [Millerson (1969)], "Watching a television programme, we feel not so much that we are being taken out into the world, as that the world is being brought to us" (pp. 201-202). Extending this idea, [Flavell, Flavell, Green, and Korfmacher (1990)] examined whether 3 and 4 year old children believed that "an object seen on videotape could be touched or could come out if the top of the set were removed, whether it would spill out of the open container it was in if the set were turned upside down, and whether a person seen on videotape could see, hear, and know about the experimenter's ongoing actions" (p. 402). The youngest children seemed to fail to make what the authors termed this image-referent distinction.

  [Reeves (1991)] suggested that even though adults don't express the beliefs that young children do, they may also fail to distinguish fully between images and referents (adults' sophistication may be the result of experience rather than development: for example, some theater-goers at the beginning of the film era are said to have panicked and run for the exits when a black and white film of an oncoming locomotive was shown [(Schoen, 1976)]). [Lombard (1995)] argued that when media users fail to distinguish between image and referent, they respond directly to what they see and hear in a mediated experience, as if what they see and hear was physically present in their viewing environment, rather than respond indirectly by decoding something they perceive only as a symbolic or representational message. A general measure of these direct responses used by [Lombard, Reich, Grabe, Campanella, and Ditton (1995)] was, "How much did you feel like it was happening to you?"

    "We are Together" (Shared Space)

  A third form of presence as transportation is found in literature concerning video conferencing as well as virtual reality. For example, in a study of video conferencing [Muhlbach, Bocker, and Prussog (1995) defined "telepresence in video communications" as "the degree to which participants of a telemeeting get the impression of sharing space with interlocutors who are at a remote physical site" (p. 301). This was measured by asking participants to report the degree to which they agreed or disagreed with statements such as "[It felt] as if we were all in the same room" and "[It felt] like a real face-to-face meeting" (p. 301). Some of the pioneers of virtual reality have suggested that its greatest potential is as a virtual gathering place in which people from around the block or around the world will be able to gather in a shared virtual space that is different from any of the individuals' "real" environments [(Lanier & Biocca, 1992)]. Precursors of these Distributed Virtual Environments (DVEs) include the popular "chat rooms" of today's Internet [(see Braham & Comerford, 1997; Rockwell, 1997; and Waters & Barrus, 1997 for detailed discussions)].

  4. Presence as immersion

  A fourth conceptualization of presence emphasizes the idea of perceptual and psychological immersion. [Biocca and Levy (1995)] note that in the most compelling virtual reality experiences, the senses are immersed in the virtual world; the body is entrusted to a reality engine. The eyes are covered by a head-mounted display; the real world is invisible. The ears are covered by headphones; ambient sound is muffled. The hands are covered by gloves or props: 'touch only the virtual bodies.' Virtual reality may share common elements with reading a book in a quiet corner, but this book has stretched in all directions and wrapped itself around the senses of the reader -- the reader is swallowed by the story. (p. 135)

  Perceptual immersion, "the degree to which a virtual environment submerges the perceptual system of the user" [(Biocca & Delaney, 1995, p. 57)], can be objectively measured by counting the number of the users' senses that are provided with input and the degree to which inputs from the physical environment are "shut out" (see [Kim, 1996]). Not only immersive virtual reality systems but also simulation rides, IMAX theaters, and even standard movie theaters can be said to immerse the senses of media users.

  Presence as immersion also includes a psychological component. When users feel immersive presence they are involved [(Palmer, 1995)], absorbed [(Quarrick, 1989)], engaged, engrossed. This psychological state typically is best measured via subject self-report (although observation of involved media users might also be a useful indicator). For example, a factor analysis of responses to items used by [Heeter (1995)] in a study of user reactions to consumer virtual reality systems resulted in an "involvement" factor containing the items "intense," "fun," "competitive," "addictive," and "exciting"; scores on this factor were the highest of all factors (8.7 out of 10).

  5. Presence as social actor within medium

  In a classic 1956 article, [Horton and Wohl] suggested that even though the relationship between a television personality and a television viewer is one-sided, with no possibility of real time interaction, skilled personalities use direct address camera views (in which the personality seems to be looking at the viewer), informal speech patterns, sincerity, and simplicity to generate a "simulacrum of conversational give and take [that] may be called para-social interaction" (p. 215). In a parasocial interaction media users respond to social cues presented by persons they encounter within a medium even though it is illogical and even inappropriate to do so. Studies have shown that people respond to interpersonal distance cues in [(Lombard, 1995), and even talk to [(Lemish, 1982)], the pictures of people on the television screen. The mediated nature of the "interaction" is ignored and the media personality is incorrectly perceived as a social actor.

  This illogical treatment of mediated entities as social actors is not limited to television. "Virtual actors" are created with digitized data from sensors attached to a real person and computer voice synthesis; the data give a computer character human gestures, facial movements, and voice (e.g., Mario, a sports mascot seen on stadium screens [(Takiff, 1993)] or "Dev," the computerized bartender/news anchor on MSNBC's "The Site"). The Microsoft personal computer software product titled "Bob" features 14 on-screen characters that guide the novice user through his or her computer's functions; Cliff Nass and Byron Reeves of Stanford University call it a "social interface" [(see Coughlin, 1996)]. Intelligent computer agents of the future will have avatars (an incarnation in human form) with which users interact [(Boyd, 1996)], making the interaction more like interacting with another human. In the software product Dogz: Your Computer Pet [(Dogz, 1995)], users adopt one of several puppies which they then teach tricks, play games with, feed, groom, pet, and discipline as their "desktop companion" grows from puppy to adult dog (a version for cats is available as well). "The Tamagotchi" ("cute little bird") is a "cyber pet" that appears on a three-quarter-inch computer screen attached to a key chain and needs constant "food, exercise, play, medicine, etc."; it is hugely popular in Japan, the Far East, and now America [(Boccella, 1997)]. And in a software product popular in Japan called Princess Maker, the user controls a female animated character:

  She's your little princess. You name her, wring your hands when she's sick, fret over her schooling. Like any caring dad you keep steady watch over her hobbies, clothes and manners. But if after all your lavish attention, she becomes a bar hostess strutting around in fishnet stockings or a club-swinging street tough -- no problem. Just reboot your computer and start again. [(Coleman, 1996, p. D3)]

  The virtual characters in similar games have their own fan clubs in Japan; a magazine, Virtual Idol, "deals not with game-playing strategy but with the hobbies, life experiences and physical measurements of [these] people who do not exist" [(Pollack, 1996)].

  In all of these examples users' perceptions and the resulting psychological processes lead them to illogically overlook the mediated or even artificial nature of an entity within a medium and attempt to interact with it; this phenomenon represents a fifth type of presence.

  6. Presence as medium as social actor

  The final conceptualization of presence involves social responses of media users not to entities (people or computer characters) within a medium, but to cues provided by the medium itself. Debate about the potential of modern computers to mimic humans officially began in 1950 with [Alan Turing's] "Turing Test" and continues today. While computers, robots, and androids in science-fiction often evoke social responses from other characters (and many audience members) because they seem so "human" (e.g., Data in Star Trek, C3P0 and R2D2 in Star Wars, Hal in 2001: A Space Odyssey, the Terminator in the Terminator films, the Replicants in Blade Runner, etc.), the phenomenon seems to exist even with today's less sophisticated computers. Nass and his colleagues at the Center for the Study of Language and Information at Stanford University have demonstrated in a series of studies [(Nass, Lombard, Henriksen, & Steuer, 1995; Nass & Moon, 1996a, 1996b; Nass, Moon, Fogg, Reeves, & Dryer, 1995; Nass & Steuer, 1994; Nass, Steuer, Henriksen, & Dryer, 1994; Nass, Steuer, Tauber, & Reeder, 1993)] that because computers use natural language, interact in real time, and fill traditionally social roles (e.g., bank teller and teacher), even experienced computer users tend to respond to them as social entities. In most of these studies a social psychology finding concerning human-human interaction is replicated in the context of human-computer interaction. For example, in human-human interaction we follow the rule "praise from others is more valid than praise from self" [(Jones, 1990; Joshi & Rai, 1987; Meyer, Mittag, & Engler, 1986; Wilson & Chambers, 1989)]. In a study by [Nass, Steuer, Henriksen, and Dryer (1994)] subjects evaluated a computer's performance in a tutoring task more favorably when the tutor computer was praised by a different computer than when it praised its own performance. These results were found despite the fact that the subjects consistently said that such responses to computers are illogical and inappropriate. Computer users also follow social rules concerning politeness and gender stereotypes. [Nass and Moon (1996a) demonstrated that these social responses are to the entity of the computer and not the person who programmed the computer.

  [Nass, Reeves, and Leshner (1996)] found an even more surprising social response to a communication technology: just as individuals consider the work of specialists in a field to be of higher quality than the work of generalists, subjects in an experiment reported that the quality of the news or entertainment programs presented on different ("specialist") television sets was higher than when the same programs were presented on just one ("generalist") set. Another example of social responses to television comes from [Lemish (1982)], who observed people watching television in public places:

  Certain viewer mannerisms suggested that television [not the people on television] was perceived as a communicative partner and not merely as a physical object. For example, viewers would rarely leave the viewing area in the middle of a segment. While it could be argued simply that viewers were involved in the program or that they were showing respect for other viewers, this observer could not avoid the impression that viewers acted as if leaving in the middle was rude and inconsiderate. (pp. 755-756)

  In these social responses to computers and televisions users again ignore, in a counter-logical way, the mediated nature of a communication experience. Basic social cues exhibited by the medium lead users to treat the medium as a social entity.

  Presence Explicated

  Although the conceptualizations discussed above vary considerably, they share a central idea. Each represents one or more aspects of what we define here formally as presence: the perceptual illusion of nonmediation. The term "perceptual" indicates that this phenomenon involves continuous (real time) responses of the human sensory, cognitive, and affective processing systems to objects and entities in a person's environment. An "illusion of nonmediation" 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. Although in one sense all of our experiences are mediated by our intrapersonal sensory and perceptual systems, "nonmediated" here is defined as experienced without human-made technology (note that under this definition even hearing aids and eyeglasses are media that "come between" our environment and our perceptual system).

  The illusion of nonmediation can occur in two distinct ways: (a) the medium can appear to be invisible or transparent and function as would a large open window, with the medium user and the medium content (objects and entities) sharing the same physical environment; and (b) the medium can appear to be transformed into something other than a medium, a social entity.

  Presence in this view can not occur unless a person is using a medium. It does not occur in degrees but either does or does not occur at any instant during media use; the subjective feeling that a medium or media-use experience produces a greater or lesser sense of presence is attributable to there being a greater or lesser number of instants during the experience in which the illusion of nonmediation occurs.

  It should be noted that this illusion does not represent a perceptual or psychological malfunction or psychosis, in which the mediated experience is consciously confused with what is nonmediated or "real." Clearly when asked, users of any current or likely future medium can accurately report that they are using a medium (the "holodeck" in the "Star Trek" television series and films is a exception; see in particular the episode of "Star Trek: The Next Generation" titled "Ship in a Bottle").

  This definition of presence can be applied to any medium and encompasses each of the six conceptualizations discussed above. A medium that becomes invisible and produces a perceptual illusion of nonmediation analogous to an open window can provide rich verbal and nonverbal information for social interaction (presence as social richness); objects and entities in such a medium should appear perceptually (if not socially) vivid and real (presence as realism); the illusion that there is no medium at work means there is no border between "this side" and "the other side" of the medium, so users can perceive that they have moved to the other side, that objects/entities from the other side have entered their immediate environment, or that they and other users are sharing a real or artificial environment (presence as transportation); the illusion of nonmediation will be more complete if the medium is perceptually and psychologically immersive (presence as immersion); and if we encounter people or entities within such a medium, even if there is no possibility of true social interaction with them, we are encouraged to respond to social cues they provide just as we would in nonmediated communication (presence as social actor within medium). Finally, when the medium itself presents us with social cues normally reserved for human-human interaction we are likely to perceive it not as a medium but as an independent social entity, a tranformed medium (presence as medium as social actor).

  Because it is a perceptual illusion, presence is a property of a person. However it results from an interaction among formal and content characteristics of a medium and characteristics of the media user, and therefore it can and does vary across individuals and across time for the same individual. We turn next to the limited evidence, as well as the speculation, concerning which of these characteristics encourage and discourage a sense of presence in media users, and the effects of presence.