Head perturbations during walking while viewing a head-fixed target

Inexpensive, head-fixed computer displays are now available that subjects can wear during locomotion. Our hypothesis is that viewing a head-fixed visual display will change the character- istics of rotational head perturbations during natural walking. Using a 3-axis angular rate sensor, we measured head rotations during natural or treadmill walking, in 10 normal subjects and 2 patients with deficient vestibular function, as they attempted to view (1) a stationary target at optical infinity; and (2) a target at a distance of 20 cm rigidly attached to the head. Normal subjects and patients showed no significant change in the predominant frequency of head rotations in any plane (ranging 0.7-5.7 Hz) during the two different viewing tasks. Mean peak head velocities also showed no difference during the two viewing conditions except in the yaw plane, in which values were greater while viewing the near target. Predominant frequencies of head rotations were similar in the pitch plane during natural or treadmill walking; however, peak velocities of pitch head rotations were substantially greater during natural walking. One vestibular patient showed modest increases of head velocity during natural walking compared with normal subjects. Rotational head perturbations that occur during natural walking are largely unaffected when subjects view a head-fixed target. There is need to study how such perturbations, which induce vestibular eye movements, affect vision of head-fixed displays.