Initial moments of adaptation to microgravity of human orientation behavior, in parabolic flight conditions.

The first ethological studies of astronauts' adaptation to microgravity dealt with the behavioral strategies observed during short-term space missions. No attempts had however been made to consider the initial moments of adaptation dynamics, when the subject is first submitted to conditions allowing body orientations in the full three dimensions of space. The present experimental approach was both longitudinal and transversal. It consisted of analysing, during a goal-directed orientation task in parabolic flight, the orientation behavior of 12 subjects with a past experience of 0, 30 or more than 300 parabolas. During each microgravity phase, the subjects were asked to orientate their bodies and touch, with the dominant hand, four coloured targets arranged inside the aircraft. Results showed that for inexperienced subjects, the time between two target contacts was longer than experienced subjects. They often failed to reach all targets in the series during the first parabolas. They showed right-left confusion and a preference for the "up-down" vertical body orientation. Their performance, described by the efficiency of orientation in all three dimensions, improved over time and according to the level of experience. The results are discussed for the spontaneous, preliminary and integrative stages of adaptation, emphasizing new relationships between the body references and those of the surroundings. Such experiences lead the subject to develop a new mental representation of space.