To quantify the normal range of visual fixation, active head movements and compensatory eye movements toward a near target were measured during head rotation in 10 normal adult subjects. The data were recorded by a photodetector for head movements and by an electronystagmograph for eye movements under the following conditions: subjects were instructed to track a 1-m distant visual target, which was moved horizontally at an amplitude of 10° and 20° over a broad frequency range changing from 0.1 to 10.0Hz for 40s in succession. The recorded data of head and eye movements were analyzed with the power spectrum analysis technique for comparison. When the frequency exceeded 5.0 Hz at an amplitude of 10°, head rotation became difficult. When the frequency was 3.8 Hz at an amplitude of 10°, the mean power spectrum of eye movements was significantly higher than that of head movements. At an amplitude of 20°, a significant difference in mean power spectrum was observed when the frequency was 1.2 Hz. The phase was stable from 0.5 to 3.0 Hz at an amplitude of 10°, and from 0.5 to 1.3 Hz at an amplitude of 20°. In quantifying visual fixation during active head rotation, it was easier and required less time to use the broad frequency range changing in succession over a short time. This method seems to be thoroughly applicable for clinical examinations.
