F Elements of a Multiuser 3-d Virtual Environment

as ICQ [1] has been used as a means of multiuser interaction. As higher bandwidth is available, multipoint videoconferencing systems such as NetMeeting [2] or CUseeMe [3] that allow people from different geographical locations to see and talk to each other are becoming popular. However, these videoconferencing systems lack the sense of immersion because each participant sees other participants in separate windows, and it is often difficult to tell who is talking to whom. Based on user study, Argyle and Dean [4] suggested that during face-to-face communication people vary physical proximity, eye contact, and other behaviors to optimize an overall level of intimacy. In addition, Tang and Isaacs [5] found that gaze awareness is important because participants can use the visual cue to determine when another participant is paying attention to them. These studies suggest that a more immersive way of multiuser communication is to connect the users in a three-dimensional (3-D) virtual environment so that users feel that they are communicating face to face. Moving from a text-based chat room environment to a 3-D environment creates new challenges in several areas such as computer animation, signal processing, and computer vision. In this article, we introduce immersive interactive technologies used in multiuser 3-D virtual environments. We also survey existing systems, some of which are detailed in other articles in this special issue.