John A. Waterworth
Eva L. Waterworth

Tools for Creativity
The Interactive Institute
SE-907 19 Umea


The Core of Presence:
Presence as Perceptual Illusion



Progress in understanding presence is inhibited by the fact that we are unable to agree what it is we are talking about. What one researcher means by presence is not the same as what another means, and from this stems confusion about how to evaluate models of presence, how to measure it, and how it relates to other psychological phenomena such as mental imagery, attention and emotional engagement. If presence is a phenomenon worthy of investigation, it has at least to be characterised in a way that differentiates it from other phenomena already under long-term investigation (such as those listed above). And this characterisation should lead to ways of measurement that can, in the best case, cleanly discriminate between changes in presence and changes in other phenomena. Over the two decades of increasingly active presence research, several definitions of what characterises presence have been put forward. We suggest that, of these, there is one that meets the needs of future progress in the field: electronically mediated presence is the perceptual illusion of being in an external environment. The key word here is perceptual, not least because of the implications it carries for measurement. We know how to measure the effectiveness of perceptual illusions objectively, and we can expect to be able to distinguish presence defined in this way from other psychological phenomena.

1 Introduction: Is there a standard view of presence?

In a recent presentation, Biocca (May, 2003) made the claim that presence researchers have been limited to a one-dimensional view of presence, whereby mediated presence (in virtual environments) competes with non-mediated presence (in the physical world) and that level of reported presence reflects the frequency of switches between the two. Although Biocca suggested that this is the standard model of presence, it has to our knowledge only been given prominence as an explicit position relatively recently (e.g. Slater et al., 2000). Be that as it may, views of presence have definitely not been confined to a single dimension. We ourselves first presented a two-dimensional model of presence at the Third International Workshop on Presence in Delft in 2000 (Waterworth, E.L. and Waterworth, J.A. 2000).


By our account, presence is primarily determined by the balance between processing internal (conceptual) information and external (perceptual) information, and it can be experienced in response to both the physical (external real) and a virtual (externally modelled) environments. In several later publications (e.g. Waterworth and Waterworth, 2001) we expanded on this two-dimensional model and extended it to include a third dimension. What we called the Focus dimension related to internal (conceptual) versus external (perceptual) modelling; what we called the Locus dimension related to presence in the physical versus a virtual world; and what we called Sensus related to the level of conscious attention, ranging from unconscious to fully alert.


Biocca’s latest position is actually quite close in some ways to the one we have proposed for several years, but there are important differences. Biocca proposes a two-dimension model, where the dimensions are spatial updating and spatial attention. The first of these ranges from virtual space to physical space, which is our Locus dimension (Waterworth and Waterworth, 2000). The second discriminates between internal, mental imagery space and external, perceptual space, which is our Focus dimension! One key difference between Biocca’s new and our own longstanding position is this: we insist that presence is primarily a perceptual phenomenon.


Biocca (May, 2003) identifies three poles at which presence may be maximised  – in the real world, in a virtual world, and in an internal mental world. The problem is that, by this account, we would always feel presence when conscious. Presence seems to have become just another word for conscious attention. In trying to solve the so-called book and dream-state problems the baby of presence has been thrown out with the bathwater of conscious attention: there is nothing left for the concept of presence to do. For us, presence is about the present, the here and now in the physical or a virtual world. The feeling one gets from absorption in an internal world (a novel, a fantasy, or whatever) is quite different, which is why healthy people almost never confuse the two (see Waterworth and Waterworth, February 2003; Riva and Waterworth, April 2003; and below). Imagined worlds are often not related to real time; a book can be put down, a line of thought can be suspended until later. We suggest that presence must be tied to the present, here and now, real time world – that is, the perceived world of the body and its surroundings – or else we had better stop calling it presence!


Our perspective is as follows. First, the book problem is not a problem! It is a confusion between sense of presence and emotional and/or intellectual engagement in internal, imagined space (Waterworth and Waterworth, February 2003). Presence has often been confused with engagement because of the prevalent use of questionnaires (we discuss measurement further in section 3 below). In these cases, metaphorical expression is mistaken for literal. When I say I can smell the sea and feel the wind when I read Moby Dick, I do not mean that literally. I do not perceive the sea or the wind, through any sense modality. The text is so engaging, the expression so vivid, that it is almost as if I do. My intellect and my emotions are engaged as if I were perceiving it, as if I were present, but I am not present and I do not feel presence.


Second, dream states are not like other cases of internal modelling. We do not normally know, at the time, that the environment we seem to be experiencing while dreaming is not real. In fact, it is so real to us that our motor systems are immobilised while we dream, otherwise we might damage ourselves and those around us In the rare cases that this defence fails, the results are shocking: we may wake up in a state of paralysis (failure to turn the defence mechanism off, or we may act out deeds totally against our normal waking nature (failure to turn the defence mechanism on); see for example, Ohayon et al. (1999). This is not the case when we imagine a situation, whether while reading a book or not. When awake, we do not confuse what we conceive in imagination with what we perceive as the external world. It is our sense of presence that supports the making of this distinction.


Both of these “problems” for a unified view of presence, and their solution, relate to the evolutionary role of presence. Looking to evolution is a key step in making further progress in the field, as we have suggested in recent publications (Waterworth and Waterworth, February 2003; Riva and Waterworth, April 2003).

2 An evolutionary view of presence

In its earliest evolutionary form presence was the sense that something was happening outside the organism in the here and now, something that could affect the organism, as opposed to being part of the organism. Initially, this may have been based in sensation (in proto consciousness) of something acting on the organism’s boundary with the environment (Humphrey, 1992). Later on in evolutionary (and neurological) terms, sensation led to perception, and presence emerged as the feeling (in core consciousness) of being in an external, perceptible world in which things happen in relation to the organism. Later still, internal modelling (in extended consciousness) allowed attention to be directed towards non-present, imagined worlds, experienced as being inside the organism (specifically, in the head: Velmans, 2000). To be useful in assessing possible scenarios, presumably their main evolutionary purpose, these imagined events evoke similar emotional responses as external events would, but not the same feeling of presence.


Once we could imagine situations and events, it then became advantageous to discriminate imagined, internal, hypothetical worlds from perceived events in the physical, external world – a discrimination that we suggest is based on the evolved form of presence. It is interesting to note that there may have been an intermediate period when this discrimination was not reliably made in this way (Jaynes, 1976, 1990), and when internal thoughts were perceived as the commands of Gods. But as consciousness extended to encompass both the outside world and an evolving internal, conceptual world, the survival advantages for organisms still reliably able to make this discrimination are obvious, and presence emerged in its current, evolved form. By this evolutionary view, presence does not discriminate between the real and the virtual, but between the internal and the external.


Clearly, evolution could not have equipped us to feel the difference between what is really present externally and what we perceive as present because of technological mediation. We can mostly tell the difference with existing virtual environments because of technical, or formal, limitations in the way the environment is coupled to the organism. But still, virtual realities do attempt to engage the organism in the same ways that the real world does, and they are more or less successful in this. The extent to which they evoke presence is to a large degree the extent to which they succeed. But this is not only a matter of emotional or intellectual engagement – which can also be stimulated by imagined situations. We may come to confuse a virtual experience with a real one because they are, in principle and as far as the organism is concerned, the same. They both evoke presence, the perception of a world surrounding the organism. And this is why virtual reality is more effective in psychotherapy than purely imaginal techniques, at least for certain conditions.


Our three-layer, evolutionary model of presence (Riva and Waterworth, 2003) suggests that maximal presence arises when proto consciousness, core consciousness and extended consciousness are focused on the same external situation or activity. As hinted at above, proto consciousness deals mostly with bodily orientation in the world (Damasio, 1999); in a VR the proto-presence layer is mostly addressed through body tracking and sensori-motor coupling. Core consciousness deals with the perceptual world of the here and now (Damasio, 1999); in a VR the core-presence layer is addressed mostly through the vividness of the various displays. Extended consciousness, as Damasio puts it (1999, page 195), “goes beyond the here and now of core consciousness, both backward and forward”. In a VR, the extended-presence layer is addressed through the content. When the other layers are integrated with core consciousness, intense presence is experienced. But when they are not integrated, presence is less strong (“unfocused”). This will happen if, for example, the body tracking (proto layer) has significant deficiencies, such as lag, or if the semantic content (extended layer) directs attention away from the display, towards the internal world of the imagination (cf. the “book problem”).


When we imagine a past situation, a possible future situation, or a fictional situation portrayed in a book, we experience some of the same emotional reactions as if we were really in the situation, by what Damasio calls the “as-if body route”. According to Damasio, this is a key aspect of our evaluations of hypothetical situations. But, this is not, for us, presence, since we never normally confuse the feeling of being in an external situation with the “as if” feeling of imagining a situation. But when extended consciousness is focused on the present, external environment, presence is enhanced. Taken together, this accounts for the fact that in a VR content may enhance or detract from the feeling of presence.


Some researchers suggest that presence is a purely formal matter, a product of the level of immersion provided by the technology of virtual reality. Slater (2003) recently made this claim most clearly, suggesting that this is a way to resolve the terminological confusion surrounding presence. We obviously sympathise with this aim, and with Slater’s position that reading a book cannot evoke a significant degree of presence. For Slater, as for us, presence is a product of perceiving and interacting with an external environment, whether real or virtual. But presence arises from attending to an external world. Even if the form of a VR is such that high presence could be experienced, by our view it will not be if the immersant is not attending to that world, if her mind is elsewhere – perhaps reliving a vivid experience in her imagination. Form is necessary but not sufficient for presence.


For us, maximal presence arises from an optimal combination of form and content. The form must provide the means for a convincing perceptual illusion, but the content should be integrated with (and so attract attention to) the form for the illusion to happen convincingly. Unlike Biocca, we do not think we always feel presence when attending to something, internal or external, nor that the internal and external are always competitive in producing presence. On the contrary, as we said earlier, the internal, “imaginal” content may either enhance or detract from the overall sense of presence. An example of enhancement is a typical computer game, where game designers strive to ensure that content and form are well integrated. Unlike Slater (2003), we do not think that we necessarily feel presence if the right form for a convincing perceptual illusion exists irrespective of content.


We find some experimental support for the views presented here in findings that presence sometimes varies with emotional content, and sometimes with form (Olsson et al., in preparation; Waterworth and Waterworth, in press). But this is an area where further research is needed (and is being conducted in, for example, the EMMA project; Alcaņiz et al., 2002). Clarifying the relation between presence and emotion is, however, complicated by the question of how we measure presence, to which we turn in the next section.

3 Measuring presence: more than questionnaires?

We can measure a psychological phenomenon in a variety of ways according to our view of what it is and what drives it, and this is reflected in the varied ways in which presence measurement has been approached. Measurement may be based on technological adequacy, subjective reports of a phenomenon, objective tests that depend on the existence of the phenomenon, or physical measures of the phenomenon happening, amongst others.


If we accept the idea that presence is a perceptual phenomenon, how do we measure it? From the perspective of experimental psychology, it does not seem adequate merely to ask an observer whether an illusion was experienced. Rather, we should look for a way of testing whether features of the display materials were reported in a way that is consistent with actually perceiving the illusion, not just imagining it (“as if”). Familiar examples include reports that indicate that equal stimuli are seen as unequal, that motion is perceived in stationary displays, that ever-rising pitch is heard in continuous patterns of sound, or that objectively straight lines are really seen as bent. It is not that the observer can imagine these things, but that the observer actually perceives things that way. In other words, we should not ask for an opinion or judgement about whether an illusion is experienced, but rather for a report that depends on the illusion being experienced.


There is an interesting parallel here with the psychological phenomenon of synaesthesia, where a stimulus in one modality produces a consistent sensation in that and another modality. Everyone can probably carry out a thought experiment, where they imagine the days of the week, say on a calendar, each having its own colour. Or, we could all do the same with a few numbers. For example, you might imagine 1 as yellow, 2 as red, 3 as brown, 4 as blue, 5 as green, and so on, and you might do this fairly consistently on different occasions (if you have a good memory). If you were shown a number by an experimenter, you could name a colour, and if you were asked if you experienced the colour, you might say that you do (in a sense, you do, because imagining colour is an experience). But, of course, unless you really are a natural synaesthete of the right variety, you do not really perceive the number as coloured! This is an analogous distinction to the one between an imagined scene and a (real or virtual) perceived scene. A true synaesthete does not imagine colours in letters or the days of the week, she really perceives them. So it is with all perceptual illusions and so, we suggest, it is with presence. Imagined presence is not presence.


The problem with questionnaires becomes clearer if we imagine questioning people about synaesthetic experiences. It is well known that many people who are not true synaesthetes claim to have such experiences (Cytowik, 1989). When asked if they associate the days of the week (or musical notes, or whatever) with colours, they will claim, not entirely falsely, that they do. But this association is not perceptual, it is imaginary or metaphorical. Such questions cannot distinguish between synaesthesia and metaphorical thinking. To report such experiences of mental imagery is simply to report “the literary mind” (Turner, 1996) in operation. In the same way, questions about presence cannot distinguish between metaphor and perception, a distinction we believe to be crucial to progress in the field.


The analogy between presence and synaesthesia can be taken further, to suggest objective tests of presence. Ramachandran and Hubbard (2001) devised several procedures to distinguish true synaesthesia from imagined (metaphorical) number colouring. In one example, a visual display showed an array of many black “5”s, with a shape (say, a triangle) of equal-sized black “2”s embedded in it. If you are not synaesthetic it will take you a long time to identify what and where the shape is. For a number-colour synaesthete, the shape perception is instantaneous, because a triangle (formed by the “2”s, seen as, say, red) will “pop out” against a background of “5”s (seen as, say, green). It is not possible to fake synaesthesia with this test, and there is no danger of its being confused with the results of a vivid imagination!


A similar test for presence as perceptual illusion might go like this. An identical room, as far as possible, might be described in text and created in a virtual reality. When the items in the room were “viewed”, in imagination or in the VR, from a certain perspective they would form a “hidden” shape of some kind. In the case of the written text, finding the hidden shape would be a slow and mentally demanding process (if possible at all, which is doubtful). In the VR, the shape would “pop out” automatically if the observer is attending to the environment. This test obviously depends on the difference between conceiving in the imagination and perceiving in the environment, between being there and imagining you are there.


If presence is, as we suggest, the feeling of involvement with the here and now of the present environment, then an obvious problem with questionnaire administration is its retrospective nature. Observers may not remember the ongoing experience accurately. By their nature and the time of administration, the questions must tap the contents of extended consciousness, what is recalled from the experience, not the core experience itself. We know that memory is affected by emotion in complex ways; remembered experiences may not be accurate reflections of the experience at the time it occurred. As far as possible, we should measure experiences through behaviour as it occurs, which is what we are trying to achieve with some sort of “perceptual pop-out” test.


From the perspective of neuro-psychology, and thus taking a non-dualistic stance on the nature of subjective experiences, we would expect that if presence really is different from other psychological phenomena it should be possible, at least in principle, to observe a specific type of brain activity that is reliably associated with other observations and subjective reports that suggest that the phenomenon is taking place. For neuro-psychology, if the phenomenon cannot be revealed in brain images, at least in principle, it does not really exist. We suggest that it should be possible, through functional brain imaging, to distinguish between imagining a textually described scene and experiencing a perception of a real or VR scene, in line with our suggestion that the former is not a case of presence, while the latter two both are.


On the other hand, we do not think it likely that the difference between presence in a virtual environment and presence in the physical one would be revealed through functional brain imaging. Since they are both cases of the same thing: perceptual attention directed to a world outside the organism. In our terms, they are both cases of presence, and so should not be distinguishable in this way. Attempts to detect shifts between the real and the virtual are in our view doomed to failure, although non-specific discontinuities of perceptual attention might be revealed.

4 Conclusions

If presence is worth researching, it must have measurable effects not wholly explainable in other terms. If presence is a distinctive psychological state, it will have a distinctive profile in terms of brain activity; a profile which can be detected through brain scanning – at least in principle. We should also be able to devise objective psychological tests of presence that do not relying on subjective opinions.


We suggest that, of the various ways of viewing presence that have been discussed, only one fits the bill. At its core, presence is the feeling we get from attending perceptually to the present world (in both time and space) outside ourselves. Mediated presence is primarily the perceptual illusion of being in an external, sharable world. It is not an internal, imaginary “thought experiment”. As our three-layer model of presence makes clear (Riva and Waterworth, April 2003), presence is often more than just perception, and mediated presence more than just a perceptual illusion. Unlike the classical, visual illusions found in psychology textbooks, contributions from other layers of consciousness can either contribute to, or detract from, the strength of the illusion of being present.


At its core, presence – in physical or virtual environments – is perceptual. The perception of an environment  is not the same thing as imagining the environment. If we could have the same experience in an imagined a room as in a VR or a real room - if they are all equally cases of presence - why should we spend money on expensive and still imperfect VR equipment? Why not just employ a good writer? Why would we be researching presence? And why would virtual reality be more effective in psychotherapy than purely imaginal techniques? It is sometimes said that VR works because the world is virtual. In some sense, this is true, but it tends to lead to the non sequitur that the imagined is the same as the virtual. We are all interested in presence not because reality is virtual, but because – for the organism if not the intellect – VR is real, in a way that mental imagery is not.


As a research community, we need to agree on a characterisation of presence that supports progress in the field. Presence is still a vague concept; researchers in the area agree that there is something important conveyed by the term, but differ widely on exactly what that something is. The main area of contention, we suggest, is how inclusive or exclusive the definition should be. As a community, we can characterise presence however we like, but a view that does not distinguish presence from other psychological phenomena, such as emotional engagement, imagination, attention, or consciousness in general will not do the job – it is too inclusive to be useful. For our current project EMMA (Alcaņiz at al., 2002) we have adopted the following definition as a basis for research on the relationship between mediated presence and emotion, in the context of mental health interventions: Presence is the subjective sensation of being there in a mediated environment yielding a perceptual illusion of non-mediation.


The shared, social aspect of perceptual worlds is, we suggest, a feature of presence that follows from this definition, and which is also compatible with our evolutionary account of its origins. As suggested earlier, it is slow and laborious to extract details from purely mental spaces, they only have one direct observer, and they are idiosyncratic to the person concerned. My experience of a novel, or any imagined space, is not the same as yours. Presence, as we have characterised it, is something that can be shared, by two or more observers perceiving the same external world (although, of course, their experiences will not be identical). This supports co-operation in coordinated action in the world. This is not the case with internal visualisations, which must be externalised in some form to be shared. The more concrete, the more directly perceptual, the form, the more similar will be the experience.


This paper has attempted to illustrate why viewing presence as primarily a perceptual phenomenon will support progress in developing both useful models and necessary tests of the experience of presence. Our view is that it is better to have a definition of presence that excludes internal, conceptual representations – such as those underlying the experience of mental imagery – since otherwise presence becomes synonymous with conscious attention. If we wish to understand how technological features, emotional engagement, and other factors influence mediated presence, we obviously need to characterise presence in a way that is neither synonymous with other factors, nor excludes them from presence research.

5 References

Alcaņiz, M, Baņos, R, Botella, C, Cottone, P, Freeman, J, Gaggioli, G, Keogh, E, Mantovani, F, Mantovani, G, Montesa, J, Perpiņá, C, Rey, B, Riva, G and Waterworth, J A (2002). The EMMA project: engaging media for mental health applications. Presented at Presence 2002. Porto, Portugal, October.

Biocca, F (2003). Can we resolve the book, the physical reality, and the dream state problems? Presentation at EU Presence Research Conference. Venice, Italy. May 7, 2003.

Csikszentmihalyi, M. (1990). Flow: The psychology of optimal experience. New York: HarperCollins

Cytowik, R (1989). Synaesthesia. Heidelberg: Springer Verlag.

Humphrey, N (1992). A History of the Mind. New York: Simon and Shuster.

Jaynes J (1976, 1990). The Origin of Consciousness in the Breakdown of the Bicameral Mind.

Lakoff, G., & Johnson, M. (1999). Philosophy In The Flesh: The Embodied Mind and Its Challenge to Western Thought. New York: Basic Books.

Olsson, S, Waterworth, E L and Waterworth, J A (in preparation). Separating Presence and Emotion. Tools for Creativity Studio, The Interactive Institute, Umeå, Sweden.

Ohayon, M M, Zulley, J, Guilleminault, C and Smirne, S, (1999) Prevalence and pathologic associations of sleep paralysis in the general population. Neurology 52: 1194

Ramachandran, V S and Hubbard, E M (2001). Synaesthesia – A Window Into Perception, Thought and Language. Journal of Consciousness Studies, 8 (12), 3-34.

Riva, G and Waterworth, J A (2003).Presence and the Self: a cognitive neuroscience approach. Presence-Connect, 3 (3), posted 07-04-2003.

Slater, M (2003). A Note on Presence Terminology. Presence-Connect, 3 (3).

Slater, M., & Steed, A. (2000). A Virtual Presence counter. Presence: Teleoperators, and Virtual Environments, 9(5), 413-434.

Turner, M (1996). The Literary Mind: the origins of thought and language. Oxford University Press.

Velmans, M (2000). Understanding Consciousness. London: Routledge

Waterworth, E L and Waterworth J A (2000) 'Using a Telescope in a Cave: Presence and Absence in Educational VR'. Presented at Presence2000: Third International Workshop on Presence, Delft, Holland, March.

Waterworth, E L and Waterworth J A (2001). Focus, Locus and Sensus: the 3 Dimensions of Virtual Experience. Cyberpsychology and Behavior, 4 (2) 203-214.

Waterworth, J A (2000) Technology in Support of Returning - From Conscious Doing to Consciously Being. Chapter based on 1998 workshop presentation at University of Lisbon. In Amoroso at al. (eds.) Science and the Primacy of Consciousness. Orinda, California, USA: The Noetic Press.

Waterworth, J. A. and Waterworth, E L (2000) Presence and Absence in Educational VR: The Role of Perceptual Seduction in Conceptual Learning, Themes in Education, 1 (1), 2000, 7-38

Waterworth, J A and Waterworth, E L (2003). The Meaning of Presence. Presence-Connect, 3 (3), posted 13-02-2003.

Waterworth, J A and Waterworth, E L (in press). Being and Time: Judged Presence and Duration as a Function of Media Form. Presence: Teleoperators and Virtual Environments (forthcoming, October 2003).