We used the magnetic search coil technique to record horizontal (yaw) and vertical (pitch) head rotations of 20 normal subjects during (1) walking in place, (2) running in place, (3) vigorous, voluntary, horizontal head rotation and (4) vigorous, voluntary, vertical head rotation. During walking or running, the predominant frequency of pitch rotations was at least twice that of yaw rotations. During running, the median, predominant pitch frequency from all subjects was 3.2 Hz, but significant harmonics were present up to 15-20 Hz in several subjects. Group median maximal head velocity during walking or running did not exceed 90 degrees/second. During vigorous, voluntary head rotations median frequency for yaw and pitch was similar and did not exceed 2.6 Hz. However, group median maximal head velocity during vigorous voluntary yaw rotation was 780 degrees/second. Thus, (1) during locomotion, the head is stabilized in space incompletely but adequately so that the vestibulo-ocular reflex (VOR) is not saturated, (2) during vigorous, voluntary head rotations, the maximum head velocity exceeds the range where the VOR can stabilize gaze, (3) the frequencies of head rotations that occur during locomotion greatly exceed frequencies conventionally used in the laboratory for testing the VOR.

1. The stability of gaze was measured in nine normal subjects during 30-s epochs of standing, walking in place, and running in place. The angle of gaze and head rotations in horizontal and vertical planes were measured using the magnetic search coil technique. Subjects visually fixed on a stationary object located at a distance of 100 m; thus measurements of gaze indicated the stability of images on the retina. 2. During standing, walking, or running in place, the standard deviation of the angle of gaze was less than 0.4 degrees, both horizontally and vertically. During standing and walking in place, peak gaze velocity (Gp) was less than 3.0 degrees/s. During running in place, Gp was less than 3.0 degrees/s horizontally but ranged up to 9.3 degrees/s vertically. 3. Visual acuity was measured during standing, walking, and running in place. During walking in place, five of nine subjects showed a small but significant (P = 0.03) decline in visual acuity compared with standing. During running in place, all nine subjects showed a small but significant (P = 0.002) decline in visual acuity compared with standing. 4. Stability of gaze was also measured during vigorous, voluntary head rotations in the horizontal (yaw) or vertical (pitch) planes, for 15-s epochs. Gp ranged as high as 70 degrees/s horizontally and 41 degrees/s vertically. All subjects reported illusory movement of the seen environment during these head rotations. 5. The suitability of linear systems techniques for analysis of the horizontal and vertical vestibuloocular reflex (VOR) during walking and running in place was assessed using coherence spectral analysis.(ABSTRACT TRUNCATED AT 250 WORDS)

We measured the stability of gaze in the horizontal and vertical planes, in 2 patients with bilaterally deficient vestibular function while they sat, stood still, walked in place, and made active horizontal and vertical head rotations. During sitting and standing, gaze was equally as stable as that in normal subjects. During walking in place, however, gaze velocity was double that of normal subjects. Thus, our patients' complaints of impaired vision and oscillopsia during walking could be ascribed to excessive motion of images on their retinas. Eye movements compensated for head rotations more effectively (higher gain) during active head rotations than during locomotion; this difference may be due to the predictable nature of active head movements. We conclude that testing of patients with vestibular symptoms should include stimuli corresponding to the rotational head perturbations that occur during locomotion; such head rotations have nonpredictable characteristics and a frequency range of 0.5 to 5.0 Hz.