Psychophysical Determination of the Phase Characteristic of the Vestibular System of Man for Sinusoidal Oscillation in Yaw

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Abstract
The phase characteristic of the vestibular system of man was determined for sinusoidal oscillation in yaw in the frequency range from 0.0025 to 0.4 Hz. Three different sets of experimental conditions were used: (1) a dark room with a fixation light; stimulus: sinusoidal rotation; (2) a dark room without a fixation light; stimulus: sinusoidal rotation + noise, and (3) a dark room without a fixation light; stimulus: sinusoidal rotation. Results: the sensation leads the velocity by about 90° at 0.005 Hz. The phase lead decreases for higher frequencies becoming nearly zero at 0.05 Hz and remaining constant in the frequency range 0.05 to 0.4 Hz. A phase lag was not found. At very low frequencies ( < 0.005 Hz), the phase lead was more than 90°. The results can be described in terms of a second-order model with time constants τ1·= 20 sec and τ2 = 0.013 sec and an adaptation term with a time constant of τa = 0.40 sec.