Richard H. Jacoby

Factors influencing operator interaction with virtual objects viewed via head-mounted see-through displays: viewing conditions and rendering latency

A head mounted visual display was used in a see through format 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. In the first experiment subjects visually traced wire paths with a head referenced cursor, subjectively rated aspects of viewing, and had their vision tested before and after monocular, biocular, or stereo viewing. Only the viewing difficulty with the biocular display was adversely effected by the visual task. This viewing difficulty is likely due to conflict between looming and stereo disparity cues. A second experiment examined the precision with which operators could manually move ring shaped virtual objects over virtual paths without collision. Accuracy of performance was studied as a function of required precision, path complexity, and system response latency. Results show that high precision tracing is most sensitive to increasing latency. Ring placement with less than 1.8 cm precision will require system latency less than 50 msec before asymptotic performance is found.

Sensor spatial distortion, visual latency, and update rate effects on 3D tracking in virtual environments

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.

Simulation Fidelity of a Virtual Environment Display

We assessed the degree to which a virtual environment system produced a faithful simulation of three-dimensional space by investigating the influence of a pitched optic array on the perception of gravity-referenced eye level (GREL). We compared the results with those obtained in a physical environment. In a within-subjects factorial design, 12 subjects indicated GREL while viewing virtual threedimensional arrays at different static orientations. A physical array biased GREL more than did a geometrically identical virtual pitched array. However, addition of two sets of orthogonal parallel lines (a grid) to the virtual pitched array resulted in as large a bias as that obtained with the physical pitched array. The increased bias was caused by the longitudinal, but not the transverse, components of the grid. We discuss implications of our results for spatial orientation models and for designs of virtual displays.

Improved temporal response in virtual environments through system hardware and software reorganization

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.

Human factors engineering of a virtual laboratory for students with physical disabilities

Medical advances, new legislation, and changing social attitudes have encouraged more students with disabilities to enter college. Educational systems consequently must continue to respond to the unique needs of these Individuals by developing adaptive educational tools. Laboratory courses requiring hands-on experience, such as physics and biology, are challenging to students with physical limitations. One promising and innovative way to provide access is through virtual environment technology, which can provide a unique tool for students with physical disabilities by offering opportunities for mobility and manipulative exploration without requiring physical access, dexterity, and strength. We are developing a virtual physics laboratory that should benefit students with physical disabilities by providing them greater control over their environment and more educational opportunities. These benefits also will be realized by nondisabled students. We discuss some of the issues and technologies employed to design the laboratory, including user needs analyses, task analyses, and assessment of current technologies.

Using virtual menus in a virtual environment

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.

Influence of Head Motion on the Judged Distance of Monocularly Presented Virtual Objects

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.