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Grabbing and manipulating virtual objects is an important user interaction for immersive virtual environments. We present implementations and discussion of six techniques which allow manipulation of remote objects.A user study of these techniques was performed which revealed their characteristics and deficiencies, and led to the development of a new class of techniques.These hybrid techniques provide distinct advantages in terms of ease of use and efficiency because they consider the tasks of grabbing and manipulation separately.

We present a categorization of techniques for firstperson motion control, or travel, through

Three-dimensional user interface design is a critical component of any virtual environment (VE) application. In this paper, we present a broad overview of 3-D interaction and user interfaces. We discuss the effect of common VE hardware devices on user interaction, as well as interaction techniques for generic 3-D tasks and the use of traditional 2-D interaction styles in 3-D environments. We divide most userinteraction tasks into three categories: navigation, selection/manipulation, and system control. Throughout the paper, our focus is on presenting not only the available techniques but also practical guidelines for 3-D interaction design and widely held myths. Finally, we briefly discuss two approaches to 3-D interaction design and some example applications with complex 3-D interaction requirements. We also present an annotated online bibliography as a reference companion to this article. IntroductionUser interfaces (UIs) for computer applications are becoming more diverse. Mice, keyboards, windows, menus, and icons-the standard parts of traditional WIMP interfaces-are still prevalent, but nontraditional devices and interface components are proliferating rapidly. These include spatial input devices such as trackers, 3-D pointing devices, and whole-hand devices allowing gestural input. Three-dimensional, multisensory output technologies-such as stereoscopic projection displays, head-mounted displays (HMDs), spatial audio systems, and haptic devices-are also becoming more common.With this new technology, new problems have also been revealed. People often find it inherently difficult to understand 3-D spaces and to perform actions in free space (Herndon, van Dam, & Gleicher, 1994). Although we live and act in a 3-D world, the physical world contains many more cues for understanding and constraints and affordances for action that cannot currently be represented accurately in a computer simulation. Therefore, great care must go into the design of user interfaces and interaction techniques for 3-D applications. It is clear that simply adapting traditional WIMP interaction styles to three dimensions does not provide a complete solution to this problem. Rather, novel 3-D user interfaces, based on real-world interaction or some other metaphor, must be developed. This paper is a broad overview of the current state of the art in 3-D user interfaces and interaction. It summarizes some of the major components of tutorials and courses given by the authors at various conferences, including the 1999 Symposium on Virtual Reality Software and Technology. Our goals are

As immersive virtual environment (VE) applications become more complex, it is clear that we need a firm understanding of the principles of VE interaction. In particular, designers need guidance in choosing three-dimensional interaction techniques. In this paper, we present a systematic approach, testbed evaluation, for the assessment of interaction techniques for VEs. Testbed evaluation uses formal frameworks and formal experiments with multiple independent and dependent variables to obtain a wide range of performance data for VE interaction techniques. We present two testbed experiments, covering techniques for the common VE tasks of travel and object selection/manipulation. The results of these experiments allow us to form general guidelines for VE interaction and to provide an empirical basis for choosing interaction techniques in VE applications. Evaluation of a real-world VE system based on the testbed results indicates that this approach can produce substantial improvements in usability.

Virtual environments (VEs) are a relatively new type of human-computer interface in which users perceive and act in a three-dimensional world. The designers of such systems cannot rely solely on design guidelines for traditional two-dimensional interfaces, so usability evaluation is crucial for VEs. This paper presents an overview of VE usability evaluation to organize and critically analyze diverse work from this field. First, we discuss some of the issues that differentiate VE usability evaluation from evaluation of traditional user interfaces such as GUIs. We also present a review of some VE evaluation methods currently in use, and discuss a simple classification space for VE usability evaluation methods. This classification space provides a structured means for comparing evaluation methods according to three key characteristics: involvement of representative users, context of evaluation, and types of results produced. Finally, to illustrate these concepts, we compare two existing evaluation approaches: testbed evaluation (Bowman, Johnson, & Hodges, 1999) and sequential evaluation .

In recent years, consumers have witnessed a technological revolution that has delivered more-realistic experiences in their own homes through high-definition, stereoscopic televisions and natural, gesture-based video game consoles. Although these experiences are more realistic, offering higher levels of fidelity, it is not clear how the increased display and interaction aspects of fidelity impact the user experience. Since immersive virtual reality (VR) allows us to achieve very high levels of fidelity, we designed and conducted a study that used a six-sided CAVE to evaluate display fidelity and interaction fidelity independently, at extremely high and low levels, for a VR first-person shooter (FPS) game. Our goal was to gain a better understanding of the effects of fidelity on the user in a complex, performance-intensive context. The results of our study indicate that both display and interaction fidelity significantly affect strategy and performance, as well as subjective judgments of presence, engagement, and usability. In particular, performance results were strongly in favor of two conditions: low-display, low-interaction fidelity (representative of traditional FPS games) and high-display, high-interaction fidelity (similar to the real world).

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