Abstract
Postural and visual motion aftereffects may be experienced after exposure to alternating periods of free fall and increased gravitoinertial force in parabolic flight. In an aftereffect, the body feels as if it is again undergoing periodic changes in force level because of motion of the substrate; strong apparent postural motion is also accompanied by visual motion of the surroundings. The aftereffects are discussed according to a) their character, b) their time course, c) secondary symptoms associated with them, d) conditions favoring their occurrence, e) their relation to the inducing frequency, f) fragments of the complete pattern, g) their duration, and h) the importance of contact cues.