A connectionist explanation of presence in virtual environments
Presence has various definitions, but can be understood as the sensation that a virtual environment is a real place, that the user is actually in the virtual environment rather than at the display terminal, or that the medium used to display the environment has disappeared leaving only the environment itself. We present an attempt to unite various presence approaches by reducing each to what we believe is a common basis – the psychology of behaviour selection and control – and re-conceptualizing presence in these terms by defining cognitive presence – the mental state where the VE rather than the real environment is acting as the basis for behaviour selection. The bulk of this work represents the construction of a three-layer connectionist model to explain and predict this concept of cognitive presence. This model takes input from two major sources: the perceptual modalities of the user (bottom-up processes), and the mental state of the user (top-down processes). These two basic sources of input competitively spread activation to a central layer which competitively determines which behaviour script will be applied to regulate behaviour. We demonstrate the ability of the model to cope with current notions of presence by using it to successfully predict two published findings: one (Hendrix & Barfield, 1995) showing that presence increases with an increase in the geometric field of view of the graphical display, and another (Salln?s, 1999), which demonstrates the positive relationship between presence and the stimulation of more than one sensory modality. Apart from this theoretical analysis, we also perform two experiments to test the central tenets of our model. The first experiment aimed to show that presence is affected by both perceptual inputs (bottom-up processes), conceptual inputs (top-down processes), and the interaction of these. We collected 103 observations from a 2x2 factorial design with stimulus quality (2 levels) and conceptual priming (2 levels) as independent variables, and as dependent variable we used three measures of presence (Slater, Usoh & Steed's scale (1995), Witmer & Singer's (1998) Presence Questionnaire and our own cognitive presence measure) for the dependent variable. We found a significant main effect for stimulus quality and a significant interaction, which created a striking effect: priming the subject with material related in theme to the content of the VE increased the mean presence score for those viewing the high quality display, but decreased the mean of those viewing the low quality display. For those not primed with material related to the VE, no mean presence difference was discernible between those using high and low quality displays. The results from this study suggest that both top-down and bottom-up activation should be taken into account when explaining the causality of presence. Our second study aimed to show that presence comes about as a result not of raw sensory information, but rather due to partly-processed perceptual information. To do this we created a simple three group comparative design, with 78 observations. Each one of the three groups viewed the same VE under three display conditions: high-quality graphical, low-quality graphical, and text-only. Using the model, we predicted that the text and low-quality graphics displays would produce the same presence levels, while the high-quality display would outperform them both. The results were mixed, with the Slater, Usoh & Steed scale showing the predicted pattern, but the Presence Questionnaire showing each condition producing a significantly different presence score (in the increasing order: text, low-quality graphics, high-quality graphics). We conclude from our studies that the model shows the correct basic structure, but that it requires some refinement with regards to its dealings with non-immersive displays. We examined the performance our presence measure, which was found to not perform satisfactorily. We conclude by proposing some points relevant to the methodology of presence research, and by suggesting some avenues for future expansion of our model.
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