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We investigated optic and somesthetic contributions to perceived body orientation in the pitch dimension. In a within-subject factorial design, each of 12 subjects attempted to set his/her body erect or 45°back from erect while restrained in a movable bed surrounded by an adjustable box. The box provided a visual environment consisting of either a grid pattern, two luminous lines, or complete darkness. Both the grid pattern and the luminous lines were effective at biasing settings of body position when the box was pitched; the pitched grid was more effective than the pitched lines. Although the pitch of the box influenced orientation to both goals, the effect was greater for the diagonal goal than for the erect goal. We present a model of postural orientation in the median plane that involves vestibular, somatosensory, and visual inputs.

A case study is presented of a fatal incident in which a man poured denatured alcohol on the wick of an alcohol stove with the intention of later lighting the wick, failed to first notice the wick had already been lit, and was engulfed in flames after the wick's flame followed the stream of fuel into the can, and caused an explosion that spewed flaming fuel onto his torso. A survey was conducted to examine common knowledge about the invisible flame of burning denatured alcohol, and showed that none of the participants were aware that denatured alcohol burned with an invisible flame before the survey, and that a small percentage recognized it as a hazard after reading the product label. The incident is evaluated from the perspective of the manufacturer's failure to guard users from the hazard of the invisible flame and their failure to warn users of the hazard.

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.