Visually induced vertical self-motion sensation is altered in microgravity adaptation.

Vertical vection is a phenomenon of self-motion perception in immobile subjects, which is conventionally perceived in the opposite direction of the upward or downward moving visual stimulus. The Austrian scientific cosmonaut experienced reversed vertical vection from sinusoidal stimulation on third and sixth day of space flight as well as immediately postflight. The occurrence of short periods of reversed vection from constant velocity stimulation six months postflight can be interpreted as a reactivation of an "alternative" visual processing mode. This may indicate that microgravity modulations of the neuronal pathways which process visual information for dynamic orientation are not completely extinguished in the processes involved in readaptation to 1-G.