The illusion of rotation or movement in an entirely different axis caused by an abrupt head movement while in a prolonged constant‑rate turn that has ceased to stimulate the brain's motion sensing system is called what?

• A. Coriolis illusion
• B. Graveyard spiral
• C. Vestibular illusion
• D. False horizon

Answer: (A)

This is about a Coriolis illusion, a vestibular illusion that happens when you move your head abruptly during or after a prolonged constant-rate turn. In a steady turn your semicircular canals adapt to the constant rotation and stop signaling rotation. If you snap your head in a different plane, signals from one canal are stimulated while others remain adapted, causing the brain to perceive rotation about a different axis than the actual motion. The result is a sense of spinning or turning in an unexpected direction, which can lead to disorientation if you rely on it instead of your instruments.

This differs from a graveyard spiral, which is a descent caused by disorientation in a coordinated turn that leads to a loss of precise pitch and bank cues, not a sudden head-movement illusion. A general vestibular illusion or a false horizon involves misperceptions of visual or vestibular cues rather than the specific cross‑axis rotation sensation produced by abrupt head motion in a turn.

So the best answer is Coriolis illusion, because it uniquely describes the cross‑axis rotation sensation resulting from abrupt head movement after vestibular adaptation in a prolonged turn.