[Frequency response of ocular counter-rolling analyzed with passive sinusoidal head roll]

Using a computerized motor-driven chair that oscillates the subject's head in the frontal plane and a real-time video processing system for analyzing torsional eye movements, the frequency response of ocular counter-rolling to passive, sinusoidal head rolling was studied in darkness in 3 normal subjects. The gain of counter-rolling increased its mean value from 0.22 (0.17 Hz) to 0.52 (1.33 Hz) along with the frequency of head oscillation. Its phase error with respect to ideal compensation was slight (173-181 deg). Furthermore, the gain of counter-rolling was increased slightly from 0.31 (+/- 5 deg) to 0.39 (+/- 20 deg) along with the amplitude of head oscillation. Our experimental results agreed with the characteristics of the frequency responses for voluntary head shaking previously reported by Collewijn and colleagues, except that counter-rolling had a slightly lower gain.