Coriolis effect

In psychophysical perception, the Coriolis effect is a form of orientational distress that can lead to nausea (also referred to as the Coriolis illusion). The Coriolis effect is a particular concern of pilots, where it can cause extreme discomfort and disorientation.

Vestibular system
The vestibular system of the ear senses balance, motion, and body position. The three semicircular canals observe angular acceleration in the three planes of motion: pitch (nod yes), yaw (twist your head no), and roll (pivot head from left to right shoulder without twisting). The otolith organs, that is, the utricle and the saccule detect linear acceleration and the tilt of the head.

The semicircular canals contain the endolymph, a fluid that shifts with angular acceleration, pressing unequally upon the two sides of a membrane, the cupula, when acceleration occurs, causing deflection of the cupula. The endolymph action lags the motion of the canal itself, due to its inertia. Under clockwise acceleration of the canal, the endolymph lags the canal, leading to a relative counterclockwise motion that is interpreted correctly as a clockwise acceleration.

If angular motion is held constant, a steady state is reached where the endolymph and the canal are moving at the same rate, the cupula no longer deflects, and the motion is not sensed. This situation is shown in the upper panel of the figure. If now the rotation abruptly stops, the canal stops rotating but the endolymph takes time to adapt, leading to a relative counterclockwise rotation of the endolymph. That counterclockwise relative rotation correctly indicates the acceleration, but leads to the false sensory interpretation of rotation in the opposite direction to what previously prevailed, even though actually all motion has stopped. The situation is shown in the bottom panel.

Mechanism
The mechanism behind the Coriolis effect is related to head motions that reorient the three semicircular canals while a person is rotating. If the head is vertical, and rotation is about the vertical axis, the semicircular canal in the horizontal plane registers the rotating motion. If rotation continues, a steady state is reached where the cupula is not deflected and the rotation is not sensed. If now the head is tilted (for simplicity) say by 90°, then the horizontal plane becomes vertical and this canal is no longer in rotation; its endolymph begins to slow down to match the motion of its canal. The subject then perceives this effect as counter-rotation about a horizontal axis, although actually no motion is occurring. At the same time, the semicircular canals previously in vertical planes are brought into a position where they must register the rotation, and their endolymphs accelerate. The combined effect of all three semicircular canals is to produce an apparent rotation in a direction unrelated to what is actually happening. It causes a sensation of rolling or pitching that is the Coriolis effect.