HEAD PERTURBATIONS DURING WALKING WHILE VIEWING A HEAD-FIXED TARGET

Background: Inexpensive, head-fixed computer displays are now availabl e that subjects can wear during locomotion. Hypothesis: Viewing a head -fixed visual display will change the characteristics of rotational he ad perturbations during natural walking. Methods: Using a 3-axis angul ar rate sensor, we measured head rotations during natural or treadmill walking, in 10 normal subjects and 2 patients with deficient vestibul ar function, as they attempted to view (A) a stationary target at opti cal infinity; and (B) a target at a distance of 20 cm rigidly attached to the head. Results: Normal subjects and patients showed no signific ant 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 degrees . s(-1)) also showed no difference during the two viewing conditions except in the yaw pla ne, in which values were greater while viewing the near target (p < 0. 005). Predominant frequencies of head rotations were similar in the pi tch plane during natural or treadmill walking; however, peak velocitie s of pitch head rotations were substantially greater during natural wa lking (p < 0.05). One vestibular patient showed modest increases of he ad velocity during natural walking compared with normal subjects. Conc lusions: Rotational head perturbations that occur during natural walki ng are largely unaffected when subjects view a head-fixed target. Ther e is need to study how such perturbations, which induce vestibular eye movements, affect vision of head-fixed displays.