Tilt bed testing of the subjective horizontal
Author(s)Dewell, Elizabeth A. (Elizabeth Anderson), 1980-
Massachusetts Institute of Technology. Dept. of Mechanical Engineering.
Charles M. Oman.
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Mittelstaedt (1987) suggested that inversion illusions which caused space sickness in astronauts was associated with a net headward bias in the body's gravireceptor organs, which could be measured on Earth using a tilting bed. Mittelstaedt showed that when individual subjects were asked to repeatedly position themselves to the gravireceptive subjective horizontal, individuals showed a small (<5 deg.) but consistent head up or head down bias that remained stable when retested weeks, months or even years later. A correlation with inversion illusion was noted in a small number of astronauts. The purpose of the present project was 1) to construct a new bed of slightly different design and 2) to verify Mittelstaedt's findings using a different subject population. Nine subjects each lay on their left side with their head immbobilized using a bite bar. They positioned the bed (and themselves) at the subjective horizontal ten successive times starting from standardized initial tilt angles which ranged from +/- 10 degrees. Tests were then repeated on right side. Four subjects returned a day later for retesting. Results showed that subjects repeatedly positioned themselves at their own subjective gravitational horizontal, which differed from true horizontal by several degrees a head down direction. Results of tests on the left and right side had similar means for most of the nine subjects; however 4 were statistically different. Left and right sides were combined, noting the above error. Mean biases in the subjective horizontal varied from -3.26 to -0.82 degrees head down between subjects, with overall mean -1.65 and s.d. 0.80. There was a statistically significant difference between responses of some subjects. Data from four subjects tested on both days was compared. A statistically significant correlation was not found, perhaps due to the small subject retest population. The differences between Mittelstaedt's data and present results are discussed.
Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2002.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Includes bibliographical references (leaf 25).
DepartmentMassachusetts Institute of Technology. Dept. of Mechanical Engineering.
Massachusetts Institute of Technology