Parabolic flight is the only ground-based condition in which weightlessness (0G) can be created long enough for safely testing changes in human perception and behavior. In addition to the 0G period, parabolic flight generates equal duration periods of 1.8G, which present another unique opportunity to test the same responses to hypergravity and back to 1G.

Spatial orientation perception is a critical subsystem that is used by the central nervous system in the control of vehicles and other complex systems in a high-level integrative function. Evidence from space flight research demonstrates that spatial orientation is altered by the transitions in gravito-inertial force levels (Clément 2011; Clément & Reschke 2008), transitions corresponding to mission phases particularly critical for crew safety and mission success. Accurate perception of self-in-space motion and self-motion relative to other objects is critical for successful operations that involve motor control e.g. doing an extra-vehicule activity or piloting the spacecraft. To date, there is only limited operational evidence that these alterations cause functional impacts on mission-critical operations and control capabilities. Immediately after space flight, most crewmembers have reported some degree of disorientation/perceptual illusion, often accompanied by nausea (or other symptoms of motion sickness), and frequently manifested by lack of coordination, particularly during locomotion The hypothesis is that alteration in sensorimotor performance induced by inverted vision is gravity depend: maximum alteration during hypergravity, intermediary alteration during normal gravity, minimal alteration during weightlessness.

Inclusion Criteria:

• Subjects will be staff member of the team or of other teams participating in the parabolic flight campaign
• Healthy volunteers (men or women)
• Aged from 21 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.

Exclusion Criteria:

• Person who took part in a previous biomedical research protocol, of which exclusion period is not terminated
• Person with medical history of oculomotor disorders
• Person with medical history of vestibular disorders
• Pregnant women