Immersion and Coherence: Research Agenda and Early Results.

Presence has been studied in the context of virtual environments for nearly thirty years, but the field has yet to reach consensus on even basic issues of definition and measurement, and there are many open research questions. We gather many of these open research questions and systematically group them according to what we believe are five key constructs that inform user experience in virtual environments: immersion, coherence, Place Illusion, Plausibility Illusion, and presence. We also report on the design and results of a study that investigated the effects of immersion and coherence on user experience in a stressful virtual visual cliff environment. In this article, each participant experienced a given VE in one of four conditions chosen from a 2x2 design: high or low levels of immersion and high or low levels of coherence. We collected both questionnaire-based and physiological metrics. Several existing presence questionnaires could not reliably distinguish the effects of immersion from those of coherence. They did, however, indicate that high levels of both together result in higher presence, compared any of the other three conditions. This suggests that "breaks in PI" and "breaks in Psi" belong to a broader category of "breaks in experience," any of which result in a degraded user experience. Participants' heart rates responded markedly differently in the two coherence conditions; no such difference was observed across the immersion conditions. This indicates that a VE that exhibits unusual or confusing behavior can cause stress in a user that affects physiological responses, and that one must take care to eliminate such confusing behaviors if one is using physiological measurement as a proxy for subjective experience in a VE.