It is suggested that a useful (if partial) measure for the quality of an interface is the degree to which it can induce presence. ``Presence'' refers to the sense of ``being in'' a computer-generated space. It is characteristic of virtual interfaces that they produce the sense that one is not simply looking at an image, but is instead inside of a space generated by the computer. Manipulations which increase the ease-of-use or intuitiveness of an interface also tend to increase the sense of presence. Conversely, a good measure for presence should tell us something about the quality of the interface.
There are certainly limitations to presence as a measure for the quality of an interface. It is a general and somewhat ambiguous measure: it does not replace task-specific performance measures. And higher presence is not always a good thing. For instance, if the task requires switching rapidly between two displays, high presence in either may impede a smooth transfer. Nevertheless, presence is an important variable to study in the search for interface goodness measures.
Both presence and simulator sickness deal with complex psychological issues. It is likely that a useful approach to these problems will have to be based on fundamental principles. The approach described in this dissertation is based on an emerging understanding of multisensory spatial perception. This dissertation summarizes a good deal of the literature on spatial perception through the ``rest frame construct'' (RFC). The RFC suggests that spatial judgments are made with respect to a ``rest frame'' (definition of what is stationary) which is not physically determined, but which is carefully maintained by the nervous system.
The most important applications of the RFC are to the measurement of presence based on spatial perception and to the reduction of simulator sickness. However, the RFC also predicts that foreground occlusions should affect presence and spatial perception. Research on all of these topics is described.