Which semicircular canals are roughly orthogonal for 3D rotation sensing?

• A. Horizontal, posterior, and superior canals.
• B. Anterior, posterior, and horizontal; all parallel.
• C. Only the horizontal canal is functional.
• D. There are four canals with no clear orthogonality.

Answer: (D)

The three semicircular canal planes form three roughly perpendicular (orthogonal) axes for sensing rotation in 3D. The horizontal (lateral) canal lies in a roughly horizontal plane, while the anterior (superior) and posterior canals lie in vertical planes that are oriented differently from the horizontal and from each other. Together on both ears, these three planes provide distinct angular acceleration signals for yaw, pitch, and roll. There are six canals in total (two per plane), not four, and they are not all parallel or limited to just the horizontal plane.