Perception of depth in microgravity during parabolic flight

This investigation examined depth and distance perception of 3-D objects presented in stereoscopic vision. The results obtained in normal gravity and microgravity in parabolic flight were compared. This experiment was performed during an ESA campaign of parabolic flight on the Airbus A300 Zero-G on six free-floating subjects. The subjects were first presented with a 3-D cube and were instructed to adjust one dimension (width, length, or height) of the cube so that all three dimensions had the same perceived length. The subjects perceived a normal cube to be taller, thinner, and shallower in microgravity compared to normal gravity. Consequently, when they adjusted its dimension so that it looked “normal” to them, they made it shorter, wider, and deeper. A simple distance perception test confirmed that the subjects underestimated the distance of objects in the depth plane in microgravity. These results confirm a role of the gravitational reference in the 3-D perception of the objects and the environment.