We examined the effects of human 3D tracking performance of several common defects of immersing virtual environments: spatial sensor distortion, visual latency and low update rates. Results show: removal of relatively small static distortion had minor effects on tracking accuracy; an adapted Cooper-Harper controllability scale proved the most sensitive subjective indicator of simulation degradation; and RMS tracking error and subjective impressions were more influenced by changing visual latency than by update rate.

Subjects immersed in a virtual room tracked an irregularly moving cube with a cursor that was controlled by their hand position. The response latency and frame rate of the system was varied. Objective tracking accuracy was compared with subjective estimates of controllability, realism, pain and disorientation. Results show that latency had a stronger effect on performance than frame rate and that the more systematically defined subjective reports, especially an adapted Cooper-Harper scale, more closely correlated with tracking performance.

Human subjects localized a monocularly viewed, space-stabilized virtual object presented on a head-mounted, see-through display. They either kept their head stationary or rocked it laterally to produce motion parallax. Their distance estimates had less variability in a head moving condition than in a head stationary condition, but in general were much less precise and much less accurate than comparable stereo-based localizations.

A see-through head-mounted visual display was used to present computer generated, space-stabilized, nearby wire-like virtual objects to 14 subjects. The visual requirements of their experimental tasks were similar to those needed for visually-guided manual assembly of aircraft wire harnesses. An experiment examined the precision with which operators can manually move ring-shaped virtual objects over virtual paths as a function of required precision (Figure 1), path complexity, and system response latency. Tasks with placement precision better than 1.8 cm will require system latency of less than 50 msec for asymptotic performance.

Excessive end-to-end latency and insufficient update rate continue to be major limitations of virtual environment (VE) system performance. Beginning from a typical baseline VE in which a spatial tracker is polled to deliver data via an RS-232 interface at each update of a single application program, we examined a series of hardware and software reconfigurations with the aim of reducing end-to-end latency and increasing update rate. These reconfigurations included: (1) multiple asynchronous UNIX processes communicating via shared memory; (2) continuous streaming rather than polled tracker operation; (3) multiple rather than single tracker instruments; and (4) higher bandwidth IEEE-488 parallel communication between tracker and computer. Starting from an average latency of 65 msec and an update rate of 20 Hz for a standard 1000 polygon test VE, our most successful implementation to date runs at 60 Hz (the maximum achievable with our graphics display hardware) with approximately 30 msec average latency. Because our equipment and architecture is based on widely available hardware (i.e., SGI computer, Polhemus Fastrak) and software (i.e., Sense8 WorldToolKit), our techniques and results are broadly applicable and easily transferable to other VE systems.

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.