Between the extremes of real life and Virtual Reality lies the spectrum of Mixed Reality, in which views of the real world are combined in some proportion with views of a virtual environment. Combining direct view, stereoscopic video, and stereoscopic graphics, Augmented Reality describes that class of displays that consists primarily of a real environment, with graphic enhancements or augmentations. Augmented Virtuality describes that class of displays that enhance the virtual experience by adding elements of the real environment. All Mixed Reality systems are limited in their capability of accurately displaying and controlled all relevant depth cues, and as a result, perceptual biases can interfere with task performance. In this paper we identify and discuss eighteen issues that pertain to Mixed Reality in general, and Augmented Reality in particular. Keywords: stereoscopic displays, augmented reality, virtual reality, depth perception, human factors Introduction The principal obj...

We compare two technological approaches to augmented reality for 3-D medical visualization: optical and video see-through devices. We provide a context to discuss the technology by reviewing several medical applications of augmented-reality research efforts driven by real needs in the medical �eld, both in the United States and in Europe. We then discuss the issues for each approach, optical versus video, from both a technology and human-factor point of view. Finally, we point to potentially promising future developments of such devices including eye tracking and multifocus planes capabilities, as well as hybrid optical/video technology. 1

With the fast advance of real-time computer graphics, head-mounted displays (HMDs) have become popular tools for 3D visualization. One of the most promising and challenging future uses of HMDs, however, is in applications where virtual environments enhance rather then replace real environments. The difficulty comes from the fact that the relative registration of real and virtual environments is a difficult task to perform from both a computational and a perceptual point of view, those being tightly correlated. Given a computational model for stereoscopic viewing, a better understanding of depth and size perception in virtual environments is called for, as well as the relationships between perceived depths and sizes of real and virtual objects sharing a common visual space. This paper first discusses the important parameters within the model that need to be carefully evaluated and set for accurate calibration of the system. We then describe the experimental paradigm used for assessing d...

Two experiments explored four factors that may influence people's judgments of exocentric (interobject) distances in virtual environments. Participants freely navigated in a simple virtual environment and repeatedly made magnitude estimations of exocentric distances. Distances were generally overestimated. An exponential model (Steven's power law) fit the data and exponent estimates were generally less than unity. Geometric field of view and the presence of feedback were found to have the strongest effect on accuracy. Display type (head-mounted vs. desktop) and the presence of additional perspective cues were less influential. Distance perception in VE's 3 . 1. Introduction In the last few years, major claims have been made about the potential efficacy of virtual environments (VE's) for training knowledge and skills (see Seidel & Chatelier, 1997; Winn, 1998). These applications generally require trainees to learn the spatial characteristics of a computer-generated environment and the...

Exploratory Studies on the Sense of Presence as a Function of Visual and Auditory Display Parameters in Virtual Environments by Claudia Mary Hendrix Chairperson of the Supervisory Committee: Professor Woodrow Barfield Department of Industrial Engineering The focus of this research was to develop subjective measures of presence in order to relate the amount of presence experienced within a virtual environment to visual and auditory display parameters. Furthermore, the research examined the relationship between presence and performance in spatial judgments. To accomplish this goal three experiments were performed; the first two experiments investigated virtual presence as a function of auditory and visual display parameters used to design virtual environments while the third study investigated presence as a function of performance measures and visual display parameters. The first experiment investigated the sense of presence within virtual environments as a function of visual display parameters while the second investigated the effect of auditory display parameters. The variables for the first experiment included the presence or absence of head tracking, the presence or absence of stereoscopic cues, and the geometric field of view (GFOV) used to design the visual display. The variables for the second experiment included the presence or absence of spatialized sound to a stereoscopic virtual environment display and the addition of spatialized versus non-spatialized sound to a stereoscopic virtual environment display. Subjects were required to navigate a virtual environment and to complete a questionnaire designed to ascertain the level of presence experienced by the participant within the virtual world. The results indicated that the reported level of presence was significa...

In this paper I describe experiments I have done using three-dimensional computer generated environments (a.k.a. "virtual worlds technology") for the tasks of process plant management and computer network monitoring. I attempt to discuss drawbacks and advantages of these, as compared to twodimensional graphic displays. In addition, I point out that verisimilitude is not always a necessary goal for "virtual realities" and that in fact, very stylised and abstract representations may be advantageous.

How the eye measures reality and virtual reality We, as a species, seem to have been fascinated with pictures throughout our history. The paintings at Niaux, Altamira, and Lascaux (Clottes, 1995; Ruspoli, 1986), for example, are known to be about 14,000 years old, but with the recently discovered paintings in the Grotte Chauvet, the origin of representational art appears to have been pushed back even further (Chauvet, Brunel Deschamps, & Hillaire, 1995; Clottes, 1996), to 20,000 years ago if not longer. 1 Thus, these paintings date from about the time at which homo sapiens sapiens first appeared in Europe (Nougier, 1969). We should remember these paintings in the context of virtual reality; our fascination with pictures is by no means recent. My intent is threefold: first, to discuss our perception of the cluttered layout, or space, that we normally find around us; second, to discuss the development of representational art up to our current appreciation of it; and third, to apply this knowledge to virtual reality systems. The first discussion focuses on the use of multiple sources of information specifying ordinal depth relations, within the theoretical framework that I have called directed perception

Head-mounted displays (HMDs) in use today have fairly limited resolution, but the extents to which this low resolution may be detrimental to various tasks is not well known. We have studied the effect of low resolution on distance perception by letting experimental subjects estimate distances to objects in computer-generated 3D scenes. The images have been presented at varying resolutions both binocularly and biocularly on a workstation screen viewed through a Cyberscope stereoscopic device and biocularly in a Flight Helmet HMD.

This study explored the impact of physically touching a virtual object on how realistic the VE seems to the user. Subjects in a "no touch" group picked up a 3-D virtual image of a kitchen plate in a VE, using a traditional 3-D wand. "See and touch" subjects physically picked up a virtual plate possessing solidity and weight, using a mixed-reality force feedback technique. Afterwards, subjects made predictions about the properties of other virtual objects they saw but did not interact with in the VE. "See and touch" subjects predicted these objects would be more solid, heavier, and more likely to obey gravity than the "no touch" group. Results provide converging evidence for the value of adding physical qualities to virtual objects. This study is the first to empirically demonstrate the effectiveness of mixed reality as a simple, safe, inexpensive technique for adding physical texture and force feedback cues to virtual objects with large freedom of motion. Examples of practical applications are discussed. Keywords: virtual reality, tactile feedback, force feedback, calibration, realism

In this licentiate thesis I study if and how computer-supported cooperative work can benefit from three-dimensional user interfaces--virtual environments. The thesis