The human sense of the head’s polarity is influenced by changes in the magnitude of gravity

The present investigation concerns the integrity of a primary mental function, the egocentric frame of reference and the sense of polarity of one’s own head. The visually perceived eye level (VPEL) and the subjective antero-posterior axis of the head were measured by means of a visual indicator in darkness during two stimulus conditions: static pitch (sagittal-plane) tilting in the 1-g environment and gondola centrifugation (2G). It is demonstrated that an increase in the magnitude of the gravitoinertial (G) force, acting in the direction of the head and body long (z) axis, causes a substantial change not only in the VPEL but also in the perceived direction of the antero-posterior axis of the head.