Interaction of Semicircular Canals and Otoliths in the Processing Structure of the Subjective Zenith

In order to discriminate between translatory and gravitational linear acceleration as well as to locate the direction of "up " (the subjective zenith, SZ) during and after movements an interaction of otoliths (linear acceleration sensors) and canals (angular velocity sensors) for human spatial orientation is necessary. Three basic assumptions underlying the present model of interaction are confirmed by experiments in which subjects were asked to adjust dynamically a display to their subjective vertical (SV) during and after motion stimuli. 1. Since translatory and gravitational acceleration cannot be measured separately, the processing structure proposed here is based on the assumption first made by Mayne1, that in a low frequency range linear acceleration is interpreted as a change of gravitational acceleration. The slow increase of the subjective vertical (SV) in the "oculogravic illusion " experiment (see FIGURE 1 or, e.g., Reference 2) validates the assumption that estimation of gravitational acceleration uses the low pass filtered otolith afferents. 2. The function of the semicircular canals is to rotate the SZ contrary to the rotation