The goal of this study is to objectively determine the perceived direction of the right-front by the subjects in weightlessness. The direction of the right-front has not been investigated to date with the measurements of the position of the eyes. The investigators will compare the intersection of the horizontal and vertical saccadic trajectories (jerky) with the apparent direction of the right-front indicated by the subjects when they look right front in the dark (LOOK) and that they indicate when they determine whether a visual target through the right-front apparent (PERCEPTION). Then, the investigators will compare these measurements between normal gravity and microgravity hypergravity during parabolic flight.

Inclusion Criteria:

• Healthy volunteers (men or women)
• Aged between 20-65 years
• Affiliates to a social security system
• Who are willing to take part in the study,
• Who gave written informed consent,
• Declared fit after a similar visit to a medical aeronautical medical fitness for the non-professional cabin crew in civil aviation. There will be no other aptitude tests for the selection of subjects.

Exclusion Criteria:

• People who participated in a biomedical research protocol for which the exclusion period is complete,
• pregnant women.