In our daily lives, the omnipresent force of gravity helps the perceptual system to integrate egocentric information arising in the eyes, head, and body into an exocentric frame of reference. With the otolith organs in our inner ear, we possess a sensory system that is specialized to detect gravity. The situations considered in this thesis make clear that the otolith system, or the vestibular system as a whole, usually operates as a silent partner. We normally don't have vestibular sensations, as we do with our visual and somatosensory system. Correspondingly, for our sense of spatial orientation to gravity we rely to a great extent on these additional "graviceptive" systems. No doubt this stems from the fact that the inputs from the orientation senses are normally cot. In certain circumstances the information provided by these sensory systems can be discordant. Two of such circumstances were investigated in this thesis. First, subjects were exposed to prolonged hypergravity in a human centrifuge, as to induce vestibular adaptation. It was assumed that the vestibular system, the otolith organs in particular, would be maladapted to normal gravity for some duration afterwards, thus providing conflicting information about the direction and magnitude of gravity. This view was based on previous observations that centrifugation causes postural imbalance and perceptual changes which may result in motion sickness, similar to the symptoms of the space adaptation syndrome seen during the first days of spaceflight. In the experiment presented in Chapter 2, the emphasis was on the otolith-induced ocular torsion (OT) response. To allow for reliable and automatic determination of OT, a new meic determination of OT, a new method for video-oculography was developed, as described in Chapter 1. In humans, the OT response is rather small. Hence, using OT in an attempt to relate the perceptual consequences of centrifugation to vestibular adaptation seemed like looking for a needle in a hay stack, while you are looking for the hay stack itself. Nevertheless, the OT measurements before and after a centrifuge run yielded evidence for otolith adaptation. Additional VOR measurements suggested that this affected canal-otolith interactions on a central level. The second situation of discordant information was created by rotating the visual surround-ings of an observer about an earth-horizontal axis. This induces the illusion of self-tilt and self-motion in the opposite direction, which is contradicted by the otolith inputs indicating a stationary body position. It was shown that the restraining influence of the otolith organs can be overridden completely by rotation of a highly polarized real visual environment (Chapter 4), resulting in compelling sensations of head-over-heels rotatiorotation, irrespective of the actual body orientation of a stationary observer. In Chapter 5 it was shown that sensations of self-tilt are temporarily enhanced by real body tilt, and that the effects do not persist after washout in which the body is returned to vertical. The former two situations were basically concerned with intersensory processes. Chapter 3, on the other hand, dealt with an intrasensory interaction within the vestibular system itself. It focused on the relative contribution of the semicircular canals and the otolith organs to the generation of the torsional VOR during sinusoidal body roll. The oculo-motor response clearly reflected an important functional difference between both vestibular subsystems: whereas the semicircular canals operate in head-centric coordinates, the otolith organs provide a link to exocentric coordinates by continuously registering the orientavity.