Interaction of labyrinthine and somatoreceptor inputs as determinants of the subjective vertical

Summary Subjects were investigated in a bed rotatable about two axes. With the head erect and the body in a standing, semi-prone or prone position (= pitch) the subject was tilted to the right to one of eight positions between 0° and 150° of roll. During eight minutes the subject aligned a luminous line with the subjective vertical (SV). Differences in the SV between the pitch positions of body were significant for roll tilts above 90°. Individuals differed in the way the SV changed between 90° and 150°, in the scatter in the settings from repeated experiments, and in the degree of influence of pitch positions (= somatoreceptor stimulation). The SV exhibited a distinct time-dependence which was different at tilts below 70° and above. It is concluded that from the two determinants of the SV one (somatoreceptors) loses effectiveness in time because of adaptive processes, while the other (labyrinth) loses effectiveness with increasing deviation of head position from the normal upright; their relative weighting differs from individual to individual.