Over the last 20 years research has been done on the question of how egocentric distances, i.e., the subjectively reported distance from a human observer to an object, are perceived in virtual environments. This review surveys the existing literature on empirical user studies on this topic. In summary, there is a mean estimation of egocentric distances in virtual environments of about 74% of the modeled distances. Many factors possibly influencing distance estimates were reported in the literature. We arranged these factors into four groups, namely measurement methods, technical factors, compositional factors, and human factors. The research on these factors is summarized, conclusions are drawn, and promising areas for future research are outlined.

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Saccadic peak velocity is affected by variations in mental workload during ecologically valid tasks. We conclude that saccadic peak velocity could be a useful diagnostic index for the assessment of operators' mental workload and attentional state in hazardous environments.

Driver fatigue is a common cause of car accidents. Thus, the objective detection of driver fatigue is a first step toward the effective management of fatigue-related traffic accidents. Here, we investigated the effects of driving time, a common inducer of driver fatigue, on the dynamics of fixational eye movements. Participants drove for 2 h in a virtual driving environment while we recorded their eye movements. Microsaccade velocities decreased with driving time, suggesting a potential effect of fatigue on microsaccades during driving.

In virtual environments, perceived distances are frequently reported to be shorter than intended. One important parameter for spatial perception in a stereoscopic virtual environment is the stereo base-that is, the distance between the two viewing cameras. We systematically varied the stereo base relative to the interpupillary distance (IPD) and examined influences on distance and size perception. Furthermore, we tested whether an individual adjustment of the stereo base through an alignment task would reduce the errors in distance estimation. Participants performed reaching movements toward a virtual tennis ball either with closed eyes (blind reaches) or open eyes (sighted reaches). Using the participants' individual IPD, the stereo base was set to (a) the IPD, (b) proportionally smaller, (c) proportionally larger, or (d) adjusted according to the individual performance in an alignment task that was conducted beforehand. Overall, consistent with previous research, distances were underestimated. As expected, with a smaller stereo base, the virtual object was perceived as being farther away and bigger, in contrast to a larger stereo base, where the virtual object was perceived to be nearer and smaller. However, the manipulation of the stereo base influenced blind reaching estimates to a smaller extent than expected, which might be due to a combination of binocular disparity and pictorial depth cues. In sighted reaching, when visual feedback was available, presumably the use of disparity matching led to a larger effect of the stereo base. The use of an individually adjusted stereo base diminished the average underestimation but did not reduce interindividual variance. Interindividual differences were task specific and could not be explained through differences in stereo acuity or fixation disparity.