Engineering topics
Publications and source records attributed to Stoper, Arnold E..
This paper presents a final technical report on Gravitational and Optical effects on Perceived Location and Orientation. Included are abstracts of these studies.
Subjects judged eye level, defined in three distinct ways relative to three distinct reference planes: a gravitational horizontal, giving the gravitationally referenced eye level (GREL); a visible surface, giving the surface-referenced eye level (SREL); and a plane fixed with respect to the head, giving the head-referenced eye level (HREL). The information available for these judgements was varied by having the subjects view an illuminated target that could be placed in a box which: (1) was pitched at various angles, (2) was illuminated or kept in darkness, (3) was moved to different positions along the subject's head-to-foot body axis, and (4) was viewed with the subjects upright or reclining. The results showed: (1) judgements of GREL made in the dark were 2.5 deg lower than in the light, with a significantly greater variability; (2) judged GREL was shifted approximately half of the way toward SREL when these two eye levels did not coincide; (3) judged SREL was shifted about 12 percent of the way toward HREL when these two eye levels did not coincide, (4) judged HREL was shifted about half way toward SREL when these two eye level did not coincide and when the subject was upright (when the subject was reclining, HREL was shifted approx. 90 percent toward SREL); (5) the variability of the judged HREL in the dark was nearly twice as great with the subject reclining than with the subject upright. These results indicate that gravity is an important source of information for judgement of eye level. In the absence of information concerning the direction of gravity, the ability to judge HREL is extremely poor. A visible environment does not seem to afford precise information as to judgements of direction, but it probably does afford significant information as to the stability of these judgements.
Subjects judged eye level in the light and in the dark by raising and lowering themselves in a dental chair until a stationary target appeared to be at the level of their eyes. This method reduced the possibility of subjects' using visible landmarks as reference points for setting eye level during lighted trials, which may have contributed to artificially low estimates of the variability of this judgment in previous studies. Chair settings were 2.5 deg higher in the dark than in the light, and variability was approximately 66 percent greater in the dark than in the light. These results are discussed in terms of possible interactions of two separate systems, one sensitive to the orientations of visible surfaces and the other sensitive to bodily and gravitational information.