The function of the vestibular system can be simplified by remembering some basic terminology of classic mechanics. All bodies moving in three dimensions have six degrees of freedom; three of these are translational, and three are rotational. The translational components may be given in terms of movements along x-, y-, and z axes of the head, which form a right-handed coordinate system for the head. The otoliths detect acceleration along all three axes as well as tilts of the head relative to gravity. Rotation of the head about these axes activates the semicircular canals, which are responsible for sensing rotational or angular accelerations of the head. Rotations about around the x-, y-, and z -axes are commonly referred to as roll, pitch, and yaw, respectively. The positive direction of head rotation follows a right-hand rule—that is, if the fingers of the right hand are curled in the direction of the arrows, the thumb points in the positive direction of the axis.

Figure 1