This paper gives HRTF magnitude data in numerical form for 43 frequencies between 0.2---12 kHz, the average of 12 studies representing 100 different subjects. However, no phase data is included in the tables; group delay simulation would need to be included in order to account for ITD. In 3-D sound applications intended for many users, we want might want to use HRTFs that represent the common features of a number of individuals. But another approach might be to use the features of a person who has desirable HRTFs, based on some criteria. (One can sense a future 3-D sound system where the pinnae of various famous musicians are simulated.) A set of HRTFs from a good localizer (discussed in Chapter 2) could be used if the criterion were localization performance. If the localization ability of the person is relatively accurate or more accurate than average, it might be reasonable to use these HRTF measurements for other individuals. The Convolvotron 3-D audio system (Wenzel, Wightman, and Foster, 1988) has used such sets particularly because elevation accuracy is affected negatively when listening through a bad localizers ears (see Wenzel, et al., 1988). It is best when any single nonindividualized HRTF set is psychoacoustically validated using a 113 statistical sample of the intended user population, as shown in Chapter 2. Otherwise, the use of one HRTF set over another is a purely subjective judgment based on criteria other than localization performance. The technique used by Wightman and Kistler (1989a) exemplifies a laboratory-based HRTF measurement procedure where accuracy and replicability of results were deemed crucial. A comparison of their techniques with those described in Blauert (1983), Shaw (1974), Mehrgardt and Mellert (1977), Middlebrooks, Makous, and Gree...

"Fish tank virtual reality" refers to the use of a standard graphics workstation to achieve real-time display of three-dimensional scenes using stereopsis and dynamic head-coupled perspective. Fish tank VR has a number of advantages over head-mounted immersion VR which make it more practical for many applications. After discussing the characteristics of fish tank VR, we describe a set of three experiments conducted to study the benefits of fish tank VR over a traditional workstation graphics display. These experiments tested user performance under two conditions: (a) whether or not stereoscopic display was used and (b) whether or not the perspective display was coupled dynamically to the positions of a user's eyes. Subjects using a comparison protocol consistently preferred headcoupling without stereo over stereo without head-coupling. Error rates in a tree tracing task similar to one used by Sollenberger and Milgram showed an order of magnitude improvement for headcoupled stereo over ...

The Virtual Reality (VR) user interface style allows natural hand and body motions to manipulate virtual objects in 3D environments using one or more 3D input devices. This style is best suited to application areas where traditional two-dimensional styles fall short, such as scienti c visualization, architectural visualization, and remote manipulation. Currently, the programming e ort required to produce a VR application is too large, and many pitfalls must be avoided in the creation of successful VR programs. In this paper we describe the Decoupled Simulation Model for creating successful VR applications, and a software system that embodies this model. The MR Toolkit simpli es the development of VR applications by providing standard facilities required by a wide range of VR user interfaces. These facilities include support for distributed computing, head-mounted displays, room geometry management, performance monitoring, hand input devices, and sound feedback. The MR Toolkit encourages programmers to structure their applications to take advantage of the distributed computing capabilities of workstation networks improving the application's performance. In this paper, the motivations and the architecture of the toolkit are outlined, the programmer's view is described, and a simple application is brie y described.

In a virtual world viewed with a head-mounted display, the user may wish to perform certain actions under the control of a manual input device. The most important of these actions are flying through the world, scaling the world, and grabbing objects. This paper shows how these actions can be precisely specified with Frame-to-frame invariants, and how the code to implement the actions can be derived from the invariants by algebraic manipulation.

A multi-user Virtual World has been implemented combining a flexible-object simulator with a multisensory user interface, including hand motion and gestures, speech input and output, sound output, and 3-D stereoscopic graphics with head-motion parallax. The implementation is based on a distributed client/server architecture with a centralized Dialogue Manager. The simulator is inserted into the Virtual World as a server. A discipline for writing interaction dialogues provides a clear conceptual hierarchy and the encapsulation of state. This hierarchy facilitates the creation of alternative interaction scenarios and shared multiuser environments.

"Well then, what about the actual getting of wisdom? Is the body in the way or not...? I mean, for example, is there any truth for men in their sight and hearing? Or as poets are forever dinning into our

Virtual environment interfaces to computer programs in several diverse application areas are currently being developed. The users of virtual environments will require many different methods to interact with the environments and the objects in them. This paper reports on our use of virtual menus as a method of interacting with virtual environments. Several aspects of virtual environments make menu interactions different from interactions with conventional menus. We review the relevant aspects of conventional menus and virtual environments, in order to provide a frame of reference for the design of virtual menus. We discuss the features and interaction methodologies of two different versions of virtual menus which have been developed and used in our lab. We also examine the problems associated with our original version, and the enhancements incorporated into our current version. 1.

this paper is funded by the U.K. Science and Engineering Research Council (SERC), and Department of Trade and Industry, through grant CTA/2 of the London Parallel Applications Centre. Thanks to Anthony Steed for his continued help with the experiments described in this paper. The Virtual Treadmill is the subject of a patent application in the UK and other countries. References

This paper reports empirical results from a study into the use of 2D widgets in 3D immersive virtual environments. Several researchers have proposed the use of 2D interaction techniques in 3D environments, however little empirical work has been done to test the usability of such approaches. We present the results of two experiments conducted on low-level 2D manipulation tasks within an immersive virtual environment. We empirically show that the addition of passive-haptic feedback for use in precise UI manipulation tasks can significantly increase user performance. Furthermore, users prefer interfaces that provide a physical surface, and that allow them to work with interface widgets in the same visual field of view as the objects they are modifying.

The study of human-computer interaction within immersive virtual environments requires us to balance what we have learned from the design and use of desktop interfaces with novel approaches to allow us to work effectively in three dimensions. While some researchers have called for revolutionary interfaces for these new environments, devoid of two-dimensional (2D) desktop widgets, others have taken a more evolutionary approach. Windowing within immersive virtual environments is an attempt to apply 2D interface techniques to three-dimensional (3D) worlds. 2D techniques are attractive because of their proven acceptance and widespread use on the desktop. With current methods of performing 2D interaction in immersive virtual environments, however, it is difficult for users of 3D worlds to perform precise manipulations, such as dragging sliders, or precisely positioning or orienting objects. We have developed a testbed designed to take advantage of bimanual interaction, proprioception, and p...