For relating
Augmented Reality to Virtual Reality later on in this work, we have to gain an
understanding of the concept of presence, that is central for any form of VR.
Asking for a definition of presence yields in several answers coming out of
different theories. This section will summarise current results compiled from
(Schuemie et al. 2001) and will be rather short. For a more extensive survey of
recent research see there.
Six different explications of presence used in literature have been identified by (Lombard & Ditton). For immersive VR the concept of transportation is the most widely used to characterise presence: the sensation of being in a virtual world (“you are there”, or “it is here”). The sense of being together in a virtual world (“we are together”) is often termed co-presence or social presence and thought to be part of overall presence. Essential is that a high sense of presence in a VE requires a simultaneous low level of presence in the real world (Slater et al.) – presence is exclusive. (Sheridan) distinguishes presence, the sense of being in a computer generated world, and telepresence, the sense of being at a real remote location. (Schloerb) gives a completely empirical definition of presence, that is subjective presence, the likelihood that the person judges himself to be physically present in the virtual environment, and objective presence, the likelihood of successfully completing a task. The concept of objective presence is regarded as rather important if it comes to VR as work environment, whereas subjective presence is questioned in this context.
In VR research
another central term is immersion. It is characterised by (Slater & Wilbur)
as an objective description of aspects of the system such as field of view and
display resolution, in contrast to presence as subjective phenomenon such as
the sensation of being in a virtual environment. Most authors quoted in this
paper are less explicit; their definition or use of the term immersion closely
resembles the meaning of subjective presence as introduced before.
The role of
attention is acknowledged in most theories suggesting explanations of presence,
e.g. (Witmer & Singer) who think that both immersion and involvement, a
psychological state experienced as consequence of focusing one’s attention on a
coherent set of stimuli or related activities and events, are necessary for
experiencing presence. The ecological view claims that the successful support
of actions with responses similar to those in the real world (where our
perceptual system has evolved) yields in a sense of presence. The social/cultural
view agrees with this notion and extends the concept as Schuemie et al.
summarises: “Experiencing presence depends on whether the VE behaves and is
constructed according to our cultural expectations and whether the VE is
perceived and interpreted the same by others (O’Brian et al. 1998)”. This
approach to presence stresses that “action is essentially social” (Mantovani
& Riva 1999).
As final definition
we want to use the one stated by (Schuemie et al.): “Presence … is a
psychological state or subjective perception in which even though part of all
of an individual’s current experience is generated by and/or filtered through
human-made technology, part or all of the individual’s perception fails to
accurately acknowledge the role of the technology in the experience.” This
means that normally, i.e. except from the most extreme cases, the person can
indicate correctly that technology is used to produce the impressions. But “at
‘some level’ and to ‘some degree’ the individual’s perceptions overlook that
knowledge and objects, events, entities, and environments are perceived as if
the technology was not involved in the experience”. Although people always can
tell apart direct from mediated stimuli and know that the experience is
mediated, the illusion of non-mediation can be perceived at some level. The
given definition is not dependent on the subjective sensation of ‘being-there’
and may also apply to less immersive experiences or even memories of past
experiences. As (Slater et al.) put it, presence makes the individual
remembering the visited environment as place rather than as a set of pictures.
Based on the results
of current research, “much uncertainty remains as to the usefulness of presence”
(Schuemie et al.). The contribution of presence on task performance is controversial
and even with more empirical evidence in the field of emotional responses
and phobia treatment it is inconclusive. Part of the problem is that it is
still unclear, “whether higher measured presence causes stronger emotional
responses in a VE or the other way around” (Schuemie et al.). But researches
acknowledge that subjective sensation can be a goal for itself. Users of certain
applications like movies, games and entertainment would benefit from higher
presence within the VE.