The purpose of the study is to investigate spatial orientation in weightlessness as it manifests not in perception but rather in motor performance by direction and reaction time of flip switch.

Hypotheses are that flip switch:

1. will be biased towards visual allocentric cues when those are available;
2. will be biased towards the egocentric reference when tactile cues are added;
3. will be dominated by egocentric cues when visual cues are not available;
4. will be delayed and more variable when confirmatory gravitational cues are absent;
5. will be faster and more reliable in absence of conflicting gravitational cues, and even more so when tactile cues are added;
6. The difference will be more pronounce when tested under Dual-task condition

Inclusion Criteria:

• Healthy volunteers (men or women)
• Aged from 20 to 65
• Affiliated to a Social Security system and, for non-French resident, holding a European Health Insurance Card (EHIC)
• Who accepted to take part in the study
• Who have given their written stated consent
• Who has passed a medical examination similar to a standard aviation medical examination for private pilot aptitude (JAR FCL3 Class 2 medical examination). There will be no additional test performed for subject selection.

Subjects will be staff member of the team or of other teams participating in the parabolic flight campaign

Exclusion Criteria:

• Person who took part in a previous biomedical research protocol, of which exclusion period is not terminated
• Person who has already participated in a parabolic flight
• Pregnant women