Vestibular sense

The vestibular mechanism is much less familiar. It is a structure of the inner ear that provides information about the state of motion and about the gravitational equilibrium of the body-or, more precisely, of the head.
The vestibular mechanism is responsive to acceleration rather than to states of regular linear motion. People adapt quickly to even the most rapid motion after acceleration has ceased and no longer experience motion through the vestibular sense. Most experimental work has been concerned with the accelerations and decelerations of rotary motion. The fairground is the traditional site of those kinetic experiences in which the vestibular sense is activated. Quite complex devices have been constructed to superimpose varieties of angular, rotatory and oscillating movement on the willing-and indeed paying-subject.
The mechanism consists principally of three fluid-filled semicircular canals set mutually at right angles and extending from a pair of central globular structures. Little is known about the central sacculus but the central utricle is responsive to gravitational force. It is a fluid-filled sac containing numerous calcified particles called otoliths that lie on top of hair-like endings. The orientation of the head in relation to the prevailing gravitational force is matched by shifts in the position of the otoliths and the degree of tilt of the head determines the rate of nervous discharge in the neurons [ 5 ] .
Each of the semicircular canals is maximally sensitive to acceleration in its own plane and it is speculated that movement in any particular plane determines a characteristic pattern of nervous discharge. There is evidence that the rate of discharge in the neurons of the semicircular canals increases when the head is rotated in one direction and diminishes on rotation in the opposite direction [61.]
It is interesting that there appear to be distinct eye movements associated with the vestibular mechanism. When motion begins, the eyes tend to drift in the direction of the motion. This drift is interspersed with rapid, automatic eye movements in the opposite direction. This state of affairs continues throughout the vestibular activity (that is to say, while acceleration is maintained) with the magnitude and frequency of the eye movements depending on the magnitude of the acceleration. When acceleration ceases, the eyes drift in the opposite direction. The common symptom of excessive vestibular stimulation, nausea, can be achieved without any movement of the subject, merely by rotating his visual field. Presumably the eye movements of true rotation are simulated.
Brook, D.,Ritchie, J. (1970) The Aesthetic Potential of the Sensory Modes, Leonardo, Vol. 3, No. 4., Oct., 1970, p. 418.