Fig. 1.

A: diagram of the 6-degrees-of-freedom vestibular stimulator. Motor-A rotated about the earth-vertical (yaw) axis and motor-B rotated about an earth-horizontal (pitch/roll) axis. The motor shaft of motor-B was affixed to the center of linear tracks. Motor-C was coupled to a belt-pulley system that moved motor-A and the superstructure, including a magnetic field cube, a laser/galvanometers assembly and a primate chamber, along a pair of linear tracks. Motor-A and the superstructure were attached to the linear tracks via a coupling shaft that could be manually locked at 15° intervals, with respect to the long axis of the tracks (“hole-and-peg locking mechanism”). Depending on the gaze direction of the monkey controlled by motor-A, motor-B produced roll or pitch motions and motor-C produced translations along the interaural (IA) or nasooccipital (NO) axis when the track was oriented horizontally. Translations along the dorsoventral (DV) axis were generated by orienting the linear tracks vertically. The yaw motor and suprastructure were manually locked to the tracks so that the animal always remained upright. Yaw, pitch, and roll were produced with the track at either orientation. B: the coordinate frame used in this study. Leftward yaw, right ear down, and pitch nose up rotations were positive rotations. Positive translations were rightward, forward, and upward.