Human-Computer Interaction and Presence in Virtual Reality

Chapter 2
In a similar vein, the generalizability of a method is hard to prove outright and is also done
by argument alone.
2.2 Presence model
In order to design a system that is effective, we will need an understanding of the way in
which the HCI affects the effectiveness of the therapy. The simplest way to do this would be
to manipulate one HCI variable at a time and observe its effect in real therapy. However, this
would be extremely time-consuming and require many therapists and patients before
significant results are obtained. We therefore need to divide the problem into smaller
problems, using intermediary concepts such as presence and fear. This way we can determine
the overall effect of HCI on effectiveness by determining the relationships between these
intermediary concepts, which are much easier to investigate and at the same time provide us
with a more thorough understanding of the underlying process. We can furthermore make
use of the considerable amount of research that has already been performed in this area.
Review of this research and the formulation of such a model are described in detail in
chapter 4.
2.2.1 Evaluation
Since this will be the first of such a model attempting to explain the effectiveness of therapy
in terms of the HCI, it is irrelevant to ask whether it is an improvement. We will only have to
show that it works. This can be tested by showing that predictions made using this model
about the UI for VRET are correct. Here, the hypothetico-deductive method is appropriate:
we can deduce hypotheses from the model and test these hypotheses using empirical data.
These hypotheses should apply to the case of VRET.
The HCI in VR includes navigation and object selection and manipulation. The interaction
most generic for all phobias and other applications than VRET as well is navigation. We will
therefore focus on the patient navigation, which can be divided into wayfinding and
locomotion. Wayfinding is the cognitive process of determining a path, locomotion is the
control of the viewpoint. In this dissertation, wayfinding techniques will not be discussed,
since the virtual environments used are relatively simple, and we assume that wayfinding has
no therapeutic value. Thus, the key HCI issues concerning the patient interaction in VRET
are related to patient locomotion: should the therapist or the patient have control over the
locomotion of the patient through the VE? If the patient is allowed control over the
locomotion, which interaction technique provides the highest effectiveness?
The presence model that will be presented in chapter 4 suggests that presence is essential to
provide the patient with fear, and that fear is essential for effective therapy. We can test the
effect of the different choices related to patient locomotion with regard to presence and fear.
First of all, we can test the effect of the choice of patient control versus therapist control:
Hypothesis 1: Locomotion controlled by the patient will increase the patient’s sense of
presence.
Hypothesis 2: Locomotion controlled by the patient will increase the fear a phobic user can
experience.
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