FIG. 9.

A: position of the left labyrinth of a monkey relative to its head. The coordinate frame of the head has been taken as the stereotaxic frame. It is the coordinate frame in which pitch (vertical), roll (torsion), and yaw (horizontal) eye movements are measured. X: pitch axis. Y: roll axis. Z: yaw axis. B: representation of the relative orientation of the coordinate axes of the stereotaxic frame (X, Y, Z) and the coordinate axes determined by the normals to the semicircular canal planes. The positive direction of these normals is determined by using a right-hand rule for the rotation direction that excites an individual canal. X_c: positive direction for the anterior canal. Y_c: positive direction for the posterior canal. Z_c: positive direction for the lateral canal. Θ₁ is the angle between the stereotaxic vertical axis (Z) and the average direction of the lateral canal axis (Z_c). Θ_υ is the angle between Z and the normal to the plane determined by X_c and Y_c. The X_c and Y_c axes are orthogonal to each other and rotated relative to the head frame about an axis normal their plane (dashed axis) by an angle ψ_v. The difference between Θ_υ and Θ₁, represents the nonorthogonality of the canal system coordinate frame.