Experimental setup.

The patient is installed on a swinging bed with eyes blinded by a mask. An electronic device (A) detects the bed’s movements and emits a beep at the beginning of each oscillation period. The movement detector is composed of an infrared emitter (A), a deflector (B) and a cover (C) placed under the bed. The cover edge was also used to measure deviation from the equilibrium position in acceleration threshold measurements. The speaker emitting the beep was placed inside the emitter box approximately 1.5 meters away from the subject’s ears.