MECHANISMS OF GAZE STABILITY DURING WALKING: BEHAVIORAL AND PHYSIOLOGICAL MEASURES RELATING GAZE STABILITY TO OSCILLOPSIA
Jeka, John J
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Visual sensory input plays a significant role in maintaining upright posture during walking. Visual input contributes to control of head, trunk, and leg motion during walking to facilitate interaction with and avoidance of objects and individuals in the environment. The vestibular system contributes to postural control during walking and also to stabilization of the eyes during head motion which may allow for more accurate use of visual information. This dissertation reports the findings of five experiments which explore how the nervous system uses vision to control upright posture during walking and also whether the act of walking contributes to gaze stability for individuals with severe vestibular loss. In the first experiment, continuous oscillatory visual scene motion was used to probe how the use of visual input changes from standing to walking and also to determine whether the trunk motion response to visual motion was the same in the medio-lateral (ML) and anterior-posterior (AP) directions. In the second experiment, visual feedback (VFB) regarding the approximate center of mass position in the ML and AP directions was used to demonstrate that ML path stability was enhanced by concurrent visual feedback for young and older adults. In the third experiment, adults with vestibular loss and healthy adults were both able to use VFB during treadmill walking to enhance ML path stability and also to separately modify their trunk orientation to vertical. The final two experiments investigated whether gaze stability was enhanced during treadmill walking compared to passive replication of sagittal plane walking head motion (seated walking) for individuals with severe vestibular loss. Individuals with severe bilateral vestibular hypofunction displayed appropriately timed eye movements which compensated for head motion during active walking compared to seated walking. Timing information from the task of active walking may have contributed to enhancement of gaze stability that was better than predictions from passive head motion. This dissertation demonstrates: 1) the importance of visual sensory input for postural control during walking; 2) that visual information can be leveraged to modify trunk and whole body walking behavior; and 3) that the nervous system may leverage intrinsic timing information during active walking to enhance gaze stability in the presence of severe vestibular disease.