Virtual reality involves the creation of multisensory experience of an environment (its space and events) through artificial, electronic means; but that environment incorporates a sufficient number of features of the non-artificial world that it is experienced as “reality.” The cognitive issues of virtual reality are those that are involved in knowing and understanding about the virtual environment (cognitive: to perceive and to know). The knowledge we are concerned with in this chapter is both short term (Where am I in the environment? What do I see? Where do I go and how do I get there?), and long term (What can and do I learn about the environment as I see and explore it?). Given the recent interest in virtual reality as a concept (Rheingold, 1991; Wexelblat, 1993; Durlach and Mavor, 1994), it is important to consider that virtual reality is not, in fact, a unified thing, but can be broken down into a set of five features, any one of which can be present or absent to create a greater sense of reality. These features consist of the following five points. 1. Three-dimensional (perspective and/or stereoscopic) viewing vs. two-dimensional planar viewing. (Sedgwick, 1986; Wickens et al., 1989). Thus, the geography student who views a 3D representation of the environment has a more realistic view than one who views a 2D contour map. 2. Dynamic vs. static display. A video or movie is more real than a series of static images of the same material. 3. Closed-loop (interactive or learner-centered) vs. open-loop interaction. A more realistic closed-loop mode is one in which the learner has control over what aspect of the learning “world” is viewed or visited. That is, the learner is an active navigator as well as an observer. 4. Inside-out (ego-referenced) vs. outside-in (world-referenced) frame-of-reference. The more realistic inside-out frame-of-reference is one in which the image of the world on the display is viewed from the perspective of the point of ego-reference of the user (that point which is being manipulated by the control). This is often characterized as the property of “immersion.” Thus, the explorer of a virtual undersea environment will view that world from a perspective akin to that of a camera placed on the explorer’s head;
Closed loop analysis of the bottleneck buffer under adaptive window controlled transfer of http-like traffic