The frequency response of the human vestibulo-ocular reflex (VOR) system was investigated by determining its amplitude and phase characteristics. The angular head velocity and the resulting angular eye velocity were measured in 7 healthy subjects using a rotation room. Rotations about a vertical axis were carried out at frequencies ranging from 0.0025 to 0.1 Hz; peak head velocity was 50°/s. From the experimental data, the gain and the phase relationship were calculated. The results appear to be in agreement with the frequency response of the theoretical transfer function which represents the VOR system. This is based on a second order differential equation for cupular behaviour, modified by an adaptation term. According to the experimental phase characteristic the cupular restoration time constant T1 was 16.6 s, and the adaptation time constant was 114 s. Linearity of the VOR system, both for amplitude and phase, was demonstrated at frequencies of 0.05 and 0.005 Hz.
The response of the vestibulo-ocular reflex (VOR) system was measured after a start or stop in angular velocity around the vertical axis. All determinations were carried out six times for 5 subjects. In a previous study, the mean value of the response T1 was calculated from the slope of the decay of the slow phase eye velocity (method a) and found to be 13.2 ± (SD) 1.4 s for CW stimulation, and 12.8 ± 1.7 s for CCW stimulation. Using the cupulometric method (b) with a fixed threshold for the slow phase eye velocity, these values are 12.1 ± 2.0 and 11.2 ± 1.4 s, respectively. The difference between the values calculated by method (a) and those calculated by method (b) is in line with the theoretical predictions as formulated in section I of this paper.
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