This paper presents a reusable, highly configurable application framework that seamlessly integrates SSVEP stimuli within a desktop-based virtual environment (VE) on standard PC equipment. Steady-state visual evoked potentials (SSVEPs) are brain signals that offer excellent information transfer rates (ITR) within brain–computer interface (BCI) systems while requiring only minimal training. Generating SSVEP stimuli in a VE allows for an easier implementation of motivating training paradigms and more realistic simulations of real-world applications. EEG measurements on seven healthy subjects within three scenarios (Button, Slalom, and Apartment) showed that moving and static software generated SSVEP stimuli flickering at frequencies of up to 29 Hz proved suitable to elicit SSVEPs. This research direction could lead to vastly improved immersive VEs that allow both disabled and healthy users to seamlessly communicate or interact through an intuitive, natural, and friendly interface.

Previous paradigms for presence research were primarily established in the context of virtual reality (VR). The objective of this paper is to introduce a new agenda for research on presence suitable for the domain of mixed reality (MR). While established assumptions and methods of presence research from VR are applicable to MR experiences, we argue that they are not necessarily meaningful or informative. Specifically, a shift of attention is needed away from psycho-physiological studies coming from a laboratory experiment tradition, toward an ecological-cultural approach that is applicable in real world situations and relies on ethnographic rather than fully controlled methods. We give a series of examples taken from the work on the European integrated research project IPCity, and discuss the implications of our findings.

This paper focuses on the distributed architecture of the collaborative threedimensional user interface management system, Studierstube. The system allows multiple users to experience a shared 3D workspace populated by multiple applications using see-through head-mounted displays or other presentation media such as projection systems. Building large, ubiquitous, or mobile workspaces requires distribution of applications over several hosts in varying and dynamic configurations. The system design is based on a distributed shared scene graph that alleviates the application programmer from explicitly considering distribution and that avoids a separation of graphical and application data. The idea of unifying all system data in the scene graph is taken to its logical consequence by implementing application instances as nodes in the scene graph. Through the distributed shared scene graph mechanism, consistency of scene graph replicas and the contained application nodes is assured. Dynamic configuration management is based on application migration between participating hosts and a spatial model of locales allowing dynamic workgroup management. We describe a number of experimental workspaces that demonstrate the use of these configuration management techniques.

Our starting point for developing the Studierstube system was the belief that augmented reality, the less obtrusive cousin of virtual reality, has a better chance of becoming a viable user interface for applications requiring manipulation of complex three-dimensional information as a daily routine. In essence, we are searching for a 3-D user interface metaphor as powerful as the desktop metaphor for 2-D. At the heart of the Studierstube system, collaborative augmented reality is used to embed computer-generated images into the real work environment. In the first part of this paper, we review the user interface of the initial Studierstube system, in particular the implementation of collaborative augmented reality, and the Personal Interaction Panel, a two-handed interface for interaction with the system. In the second part, an extended Studierstube system based on a heterogeneous distributed architecture is presented. This system allows the user to combine multiple approaches— augmented reality, projection displays, and ubiquitous computing—to the interface as needed. The environment is controlled by the Personal Interaction Panel, a twohanded, pen-and-pad interface that has versatile uses for interacting with the virtual environment. Studierstube also borrows elements from the desktop, such as multitasking and multi-windowing. The resulting software architecture is a user interface management system for complex augmented reality applications. The presentation is complemented by selected application examples.

This paper introduces the Spatially Extended Anchoring Mechanism (SEAM) as a 3-D user-interface metaphor to connect virtual worlds and manage scalability in distributed virtual environments. SEAMs provide a visual and navigable connection between worlds to manage both the complexity of rendering and network communication typically occurring in such environments. In the context of augmented reality, SEAMs can be applied as a 3-D window interface. A rendering algorithm is described which performs well on the graphics accelerators of standard personal computers.