Bernard D. Adelstein

Perceptual decomposition of virtual haptic surfaces

The analysis and construction of virtual haptic surfaces are considered from a perceptual point of view rather than from the dynamics and controls approach of prior work. The authors developed a perceptual decomposition of surface contact sensation by examining three qualities associated with the different stages of interaction with a haptic wall simulation. These qualities are the crispness of initial contact, the hardness of surface rigidity, and the cleanness of final release from the virtual walls surface. These qualities, plus an overall rating of wall quality, were employed consistently by seven subjects to evaluate a set of six simple haptic wall simulations. Three of the wall models consisted of single linear springs; the remainder, single viscous dampers. Highest rankings of subjective hardness were associated with the spring models; damper models received the highest crispness rankings. Subjects favored the simple spring models as having, overall, the more wall-like perceptual character.<<ETX>>

Calculus of Nonrigid Surfaces for Geometry and Texture Manipulation

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 users subjective response is a demand characteristic resulting from pre and posttest measures. In this study, subjects were given either SSQs 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 discussedThe 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 users subjective response is a demand characteristic resulting from pre and posttest measures. In this study, subjects were given either SSQs 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 discussedThe 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 users subjective response is a demand characteristic resulting from pre and posttest measures. In this study, subjects were given either SSQs 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.

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 users subjective response is a demand characteristic resulting from pre and posttest measures. In this study, subjects were given either SSQs 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 discussedThe 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 users subjective response is a demand characteristic resulting from pre and posttest measures. In this study, subjects were given either SSQs 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 discussedThe 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 users subjective response is a demand characteristic resulting from pre and posttest measures. In this study, subjects were given either SSQs 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.

HEAD TRACKING LATENCY IN VIRTUAL ENVIRONMENTS: PSYCHOPHYSICS AND A MODEL

Quantification of perceptual sensitivity to latency in virtual environments (VEs) and elucidation of the mechanism by which latency is perceived is essential for development of countermeasures by VE designers. We test the hypothesis that observers use “image slip” (i.e., motion of the VE scene caused by system time lags) to detect the consequences of latency rather than explicitly detecting time delay. Our presumption is that forcing observers to change from constant rate to randomly paced head motion will disrupt their ability to discriminate latency based on perceived image slip. This study indicates that the disruption in motion pattern causes a shift in latency detection criteria and a minor degradation in discrimination ability. It is likely therefore that observers make at least some use of image slip in discriminating VE latency. It can also be inferred that when observers learn to discriminate latency, their Just Noticeable Difference (JND) remains below 17 ms.

Sensitivity to haptic-audio asynchrony

The natural role of sound in actions involving mechanical impact and vibration suggests the use of auditory display as an augmentation to virtual haptic interfaces. In order to budget available computational resources for sound simulation, the perceptually tolerable asynchrony between paired haptic-auditory sensations must be known. This paper describes a psychophysical study of detectable time delay between a voluntary hammer tap and its auditory consequence (a percussive sound of either 1, 50, or 200 ms duration). The results show Just Noticeable Differences (JNDs) for temporal asynchrony of 24 ms with insignificant response bias. The invariance of JND and response bias as a function of sound duration in this experiment indicates that observers cued on the initial attack of the auditory stimuli.

Generalizeability of Latency Detection in a Variety of Virtual Environments

User perceptual sensitivity to changes of system latency was tested in three simple virtual environments: one with only a foreground object, a second with only a background object, and a third that combined both of these elements. Prior psychophysical measurements of sensitivity, Just Noticeable Difference; and bias, Points of Subjective Equality, from our laboratory are confirmed with measurements in 13 subjects. Our measurements indicate that perceptual stability across a variety of virtual environments will require latencies less than 16 ms. We discount a possible explanation that the differences between our results and those from a study by Allison et al. could be related to a visual capture effect initially reported by L. Matin. Instead, the differences may be due to the type of psychophysical judgment rendered by the subjects and the degree to which subjects were instructed and practiced.

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.

Discriminability of Prediction Artifacts in a Time-Delayed Virtual Environment:

Overall latency remains an impediment to perceived image stability and consequently to human performance in virtual environment (VE) systems. Predictive compensators have been proposed as a means to mitigate these shortcomings, but they introduce rendering errors because of induced motion overshoot and heightened noise. Discriminability of these compensator artifacts was investigated by a protocol in which head tracked image stability for 35 ms baseline VE system latency was compared against artificially added (16.7 to 100 ms) latency compensated by a previously studied Kalman Filter (KF) predictor. A control study in which uncompensated 16.7 to 100 ms latencies were compared against the baseline was also performed. Results from 10 subjects in the main study and 8 in the control group indicate that predictive compensation artifacts are less discernible than the disruptions of uncompensated time delay for the shorter but not the longer added latencies. We propose that noise magnification and overshoot are contributory cues to the presence of predictive compensation.

A Frequency-Domain Analysis of Haptic Gratings

The detectability and discriminability of virtual haptic gratings were analyzed in the frequency domain. Detection (Exp. 1) and discrimination (Exp. 2) thresholds for virtual haptic gratings were estimated using a force-feedback device that simulated sinusoidal and square-wave gratings with spatial periods from 0.2 to 38.4 mm. The detection threshold results indicated that for spatial periods up to 6.4 mm (i.e., spatial frequencies >0.156 cycle/mm), the detectability of square-wave gratings could be predicted quantitatively from the detection thresholds of their corresponding fundamental components. The discrimination experiment confirmed that at higher spatial frequencies, the square-wave gratings were initially indistinguishable from the corresponding fundamental components until the third harmonics were detectable. At lower spatial frequencies, the third harmonic components of square-wave gratings had lower detection thresholds than the corresponding fundamental components. Therefore, the square-wave gratings were detectable as soon as the third harmonic components were detectable. Results from a third experiment where gratings consisting of two superimposed sinusoidal components were compared (Exp. 3) showed that people were insensitive to the relative phase between the two components. Our results have important implications for engineering applications, where complex haptic signals are transmitted at high update rates over networks with limited bandwidths.