Designing Virtual Reality Systems (PDF)

computational resources required by the nature of the given task are not usually immediately available and ‘‘satisificing’’ (satisfy þ sacrifice) solutions must be often made (e.g., high efficiency but low sense of presence or vice versa). Structured Approach to the Interaction / Interface Design In discussing 3D multimodal interaction, we first make an important distinction between two terminologies: interaction and interface. Interaction is an abstract model that describes how a user accomplishes some tasks. Interface is a specialized choice of hardware and software through which a user communicates with the computer system (a particular implementation of the interaction model; see Figure 8.1).

The key to a good interaction design is to carefully model the given task, and propose a set of interfaces that satisfice the multidimensional criteria of presence, naturalness, and efficiency. As with any design, interaction design also goes through the iterative phases of synthesis/modification and evaluation, for the lack of established design methodology (compared to the maturity for the 2D interface counterpart). This is partly because the sensor and display technologies (and their cost) are continually changing and the goals of interaction design are often conflicting. Moreover, the evaluation criteria are often loosely defined.

Although for interaction efficiency, quantitative measures of task performance such as the completion time and error rate can be used, presence, user preference, and naturalness are quite subjective, and correct evaluation of interaction design with respect to these subjective criteria would ideally require a usability experiment with a large number of subjects. This is often practically an impossible thing to do in an iterative design process. There is no complete established methodology in 3D multimodal interaction design, however, a few guidelines from prior and ongoing research do exist [Bow05] and they can be applied effectively to reduce the trial-and-error cycles and overcome the dependence on sole experience.