Tilt bed testing of the subjective horizontal

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.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Mechanical Engineering.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2002

Author dc:creator

• Dewell, Elizabeth A. (Elizabeth Anderson), 1980-

Advisor dc:contributor.advisor

• Charles M. Oman.

• Mechanical Engineering.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/69235

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/69235