Frequency Response of the Human Vestibulo-Ocular Reflex System at Low Frequencies: The Effect of Adaptation

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Abstract
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.

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