Head perturbations during walking while viewing a head-fixed target

Background: Inexpensive, head-fixed computer displays are now available that subjects can wear during locomotion. Hypothesis: Viewing a head-fixed visual display will change the characteristics of rotational head perturbations during natural walking. Methods: 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 (A) a stationary target at optical infinity; and (B) a target at a distance of 20 cm rigidly attached to the head. Results: 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 (p > 0.1). Mean peak head velocities (ranging 6-36° · s^-1) also showed no difference during the two viewing conditions except in the yaw plane, in which values were greater while viewing the near target (p < 0.005). 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 (p < 0.05). One vestibular patient showed modest increases of head velocity during natural walking compared with normal subjects. Conclusions: 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.