A Simple Video-Based Technique for Measuring Latency in Virtual Reality or Teleoperation.

Designers of virtual reality (VR) systems are aware of the need to minimize delays between the user's tracked physical actions and the consequent displayed actions in the virtual environment. Such delays, also referred to as end-to-end latency, are known to degrade user performance and even cause simulator sickness. Though a wide variety of hardware and software design strategies have been used to reduce delays, techniques for measuring and minimizing latency continue to be needed since transmission and switching delays are likely to continue to introduce new sources of latency, especially in wireless mobile environments. This article describes a convenient low-cost technique for measuring end-to-end latencies using a human evaluator and an ordinary consumer camera (e.g., cell phone camera). Since the technique does not depend upon the use of specialized hardware and software, it differs from other methods in that it can easily be used to measure latencies of systems in the specific hardware and software configuration and the relevant performance environments. The achievable measurement accuracy was assessed in an experimental trial. Results indicate a measurement uncertainty below 10 ms. Some refinements to the technique are discussed, which may further reduce the measurement uncertainty to approximately 1 ms.

The Effect of Focal Distance, Age, and Brightness on Near-Field Augmented Reality Depth Matching.

Many augmented reality (AR) applications operate within near-field reaching distances, and require matching the depth of a virtual object with a real object. The accuracy of this matching was measured in three experiments, which examined the effect of focal distance, age, and brightness, within distances of 33.3 to 50 cm, using a custom-built AR haploscope. Experiment I examined the effect of focal demand, at the levels of collimated (infinite focal distance), consistent with other depth cues, and at the midpoint of reaching distance. Observers were too young to exhibit age-related reductions in accommodative ability. The depth matches of collimated targets were increasingly overestimated with increasing distance, consistent targets were slightly underestimated, and midpoint targets were accurately estimated. Experiment II replicated Experiment I, with older observers. Results were similar to Experiment I. Experiment III replicated Experiment I with dimmer targets, using young observers. Results were again consistent with Experiment I, except that both consistent and midpoint targets were accurately estimated. In all cases, collimated results were explained by a model, where the collimation biases the eyes' vergence angle outwards by a constant amount. Focal demand and brightness affect near-field AR depth matching, while age-related reductions in accommodative ability have no effect.

Effect of reduced stereoscopic camera separation on ring placement with a surgical telerobot.

BACKGROUND: A custom, stereoscopic video camera was built to study the impact of decreased camera separation on a stereoscopically viewed, visual-manual task resembling some aspects of surgery. MATERIALS AND METHODS: Twelve naïve subjects and one of the experimenters were first trained in a ring placement task using the stereo-laparoscope and subsequently switched to the stereo-camera, which was used with differing camera separations ranging from 100% of the laparoscope's separation to a biocular view corresponding to no separation (2D). RESULTS: The results suggest firstly, that stereopsis (i.e., use of 3D laparoscopes) improves surgical performance over conventional 2D laparoscopes, and secondly that camera separation may be reduced 20-35% without appreciably degrading user performance. Even a 50% reduction in separation resulted in stereoscopically supported performance far superior compared to the 2D condition. CONCLUSIONS: The results suggest that existing 3D laparoscopes which use 5-mm camera separation may well be significantly miniaturized without causing substantial performance degradation.

Demand characteristics in assessing motion sickness in a virtual environment: or does taking a motion sickness questionnaire make you sick?

The experience of motion sickness in a virtual environment may be measured through pre and postexperiment self-reported questionnaires such as the Simulator Sickness Questionnaire (SSQ). Although research provides converging evidence that users of virtual environments can experience motion sickness, there have been no controlled studies to determine to what extent the user's subjective response is a demand characteristic resulting from pre and posttest measures. In this study, subjects were given either SSQ's both pre and postvirtual environment immersion, or only postimmersion. This technique tested for contrast effects due to demand characteristics in which administration of the questionnaire itself suggested to the participant that the virtual environment may produce motion sickness. Results indicate that reports of motion sickness after immersion in a virtual environment are much greater when both pre and postquestionnaires are given than when only a posttest questionnaire is used. The implications for assessments of motion sickness in virtual environments are discussed.

Matching and reaching depth judgments with real and augmented reality targets.

Many compelling augmented reality (AR) applications require users to correctly perceive the location of virtual objects, some with accuracies as tight as 1 mm. However, measuring the perceived depth of AR objects at these accuracies has not yet been demonstrated. In this paper, we address this challenge by employing two different depth judgment methods, perceptual matching and blind reaching, in a series of three experiments, where observers judged the depth of real and AR target objects presented at reaching distances. Our experiments found that observers can accurately match the distance of a real target, but when viewing an AR target through collimating optics, their matches systematically overestimate the distance by 0.5 to 4.0 cm. However, these results can be explained by a model where the collimation causes the eyes' vergence angle to rotate outward by a constant angular amount. These findings give error bounds for using collimating AR displays at reaching distances, and suggest that for these applications, AR displays need to provide an adjustable focus. Our experiments further found that observers initially reach ∼4 cm too short, but reaching accuracy improves with both consistent proprioception and corrective visual feedback, and eventually becomes nearly as accurate as matching.

Kinesthetic compensation for sensorimotor rearrangements.

The authors report a new sensorimotor phenomenon in which participants use hand-sensed kinesthetic information to compensate for rotational sensorimotor rearrangements. This compensation benefits from conscious awareness and is related to hand posture. The technique can reduce control inefficiency with some misalignments by as much as 64%. The results support Y. Guiard's (1987) suggestion that in bimanual tasks one hand provides an operational frame of reference for the other hand as in a closed kinematic chain. Results with right-handed participants show that the right and left hands are equally effective at providing such a cue. A constant-angular-targeting-error model, similar to that used for hand movements by H. Cunningham and I. Vardi (1990) and for walking by S. K. Rushton, J. M. Harris, M. R. Lloyd, and J. P. Wann (1998), is used to model the trajectories of targeting hand movements demonstrating the phenomenon. The model provides a natural parameter of the error.