GOAL-DIRECTED LINEAR LOCOMOTION IN NORMAL AND LABYRINTHINE-DEFECTIVE SUBJECTS

When a subject is walking blindfolded straight ahead towards a previou sly seen target, the brain must update an internal representation with respect to the environment. This study examines whether the informati on given by the vestibular system is necessary for this simple path in tegration task and gives a quantitative description of locomotor behav iour during the walk by comparing ten normal and seven bilateral labyr inthine-defective (LD) subjects. Each subject performed 20 blindfolded walks (EC) and ten walks with eyes open (EO) towards a target attache d to the floor 4 m in front of them; these walks were made at differen t velocities. The positions of head, trunk and feet were recorded usin g a 3D motion analysis system. No significant difference was found bet ween, normal and LD groups in-terms of the distance error of reaching the target, while LD subjects showed a larger lateral error. Patch cur vature, expressed as the standard deviation of the angle between the d irection of one step and straight ahead, was found to be significantly larger for LD subjects in the EC condition, demonstrating their insta bility when walking without vision. Mean walking velocity was lower fo r LD subjects than for normal subjects in both EC and EO conditions. B oth groups walked faster with eyes open; LD subjects increased their v elocity by increasing step length, normal subjects by increasing step frequency. Head stabilisation in the frontal plane during locomotion w as not significantly different between LD and normal subjects, whereas both head and trunk rotation were slightly larger in LD subjects duri ng blindfolded walking. The results show that bilateral LD subjects ar e able to perform linear goal-directed locomotion towards memorised ta rgets. Thus, the vestibular system does not appear to be necessary for active linear path integration.