Eight healthy volunteers and one vestibular patient were asked to walk around an obstacle (a 1.8-meter-high tripod) and to reach a final position indicated by a target. The optimal trajectory corresponded to a 90° corner. The experiment was repeated in two conditions, in light and with blindfolds and at three different walking speeds. Instantaneous head orientation and walking direction were calculated by means of a 4-camera ELITE system operating at 100 Hz, which sampled the position of two markers aligned with the head naso-occipital axis. The "subjective" position of the corner with respect to the trajectory performed (both in darkness and in light) was assumed to be coincident with the maximum of the trajectory curvature.
Healthy subjects turned their heads toward the direction of the target before
they arrived at the corner position. This point corresponded to a maximum deviation
fo the head with the respect to the direction of the trajectory (between 15°
and 30°, depending on the walking speed). Afterwards the trajectory realigned
to the head direction. The same pattern occurred in darkness.
The patient showed a directional asymmetry in the trajectory and an abnormal
head anticipatory pattern when he turned toward the ill side.