The Effects of Visual Feedback Distortion with Unilateral Leg Loading on Gait Symmetry CARLOS TOBAR, 1 EVA MARTINEZ, 1 NADA RHOUNI, 2 and SEUNG-JAE KIM 1,3 1 Biomedical Engineering, California Baptist University, Riverside, CA 92504, USA; 2 College of Health Science, California Baptist University, Riverside, CA 92504, USA; and 3 The Gordon and Jill Bourns College of Engineering, California Baptist University, 8432 Magnolia Avenue, Riverside, CA 92504, USA (Received 2 August 2017; accepted 3 November 2017; published online 8 November 2017) Associate Editor Thurmon E. Lockhart oversaw the review of this article. Abstract—Our prior work provides evidence that visual feedback distortion drives an implicit adaptation; a gradual distortion of visual representation of step length modulated subjects’ step lengths away from symmetry. To further explore the effect of the visual feedback distortion on unconscious change in step symmetry, we investigated whether such adaptation would occur even in the presence of altered limb mechanics by adding mass to one side of the leg. 26 subjects performed three 8–min trials (weight only, weight plus visual feedback, and weight plus visual feedback distortion) of treadmill walking. During the weight only trial, the subjects wore a 5 lb mass around the right ankle. The modification of limb inertia caused asymmetric gait. The visual feedback showing right and left step length informa- tion as bar graphs was displayed on a computer screen. To add visual feedback distortion, we increased the length of one side of the visual bars by 10% above the actual step length, and the visual distortion was implemented for the side that took longer in response to the added mass. We found that even when adjustments were made to unilateral loading, the subjects spontaneously changed their step symmetry in response to the visual distortion, which resulted in a more symmetric gait. This change may be characterized by sensory prediction errors, and our results suggest that visual feedback distortion has a significant impact on gait symmetry regard- less of other conditions affecting limb mechanics. A rehabil- itation program employing visual feedback distortion may provide an effective way to restore gait symmetry. Keywords—Gait adaptation, Visual feedback distortion, Gait Symmetry, Gait rehabilitation. INTRODUCTION Many musculoskeletal conditions and neurological disorders such as stroke, cerebral palsy, Parkinson’s disease, or spinal cord injury affect gait symmetric patterns. 5,6,9,20,30 Spatiotemporal asymmetries chal- lenge patients resulting in reductions in gait speed, stability of balance, efficiency of walking, and their activity levels. 1,27,28 Thus, gait rehabilitation targeting gait symmetry addresses an important and significant issue. Although treadmill training is a widely used method of gait rehabilitation for the improvement of general gait functions including gait symmetry, 29 it is not sufficiently interactive to promote more efficient motor learning. 7,19 Interactive rehabilitation programs potentially entail an effective adaptive motor learning process resulting in better functional outcomes, 3,33 and visual feedback is one form of effective interactive training. 39,44 Providing visual feedback of subjects’ motion or performance in the context of computer games, virtual environments, or split-belt treadmill training offers an attractive complement to conven- tional therapy during balance or gait symmetry train- ing in Parkinson’s disease, cerebral palsy, and strokes. 22,23,41 In line with the further development of an interactive and more efficient gait rehabilitation program with visual feedback, we previously presented a rehabilitative paradigm called visual feedback dis- tortion in which the visual representation of step length symmetry was manipulated. 12 In the previous studies, we implicitly distorted the visual representation of step length, and subjects walked without knowledge of the distortion. Even with a distraction task added or ex- plicit knowledge of the visual distortion, subjects adapted to the imposed distortion of visual feedback by spontaneously modulating their gait symmetric Address correspondence to Seung-Jae Kim, The Gordon and Jill Bourns College of Engineering, California Baptist University, 8432 Magnolia Avenue, Riverside, CA 92504, USA. Electronic mail: sjkim@calbaptist.edu Annals of Biomedical Engineering, Vol. 46, No. 2, February 2018 (Ó 2017) pp. 324–333 https://doi.org/10.1007/s10439-017-1954-x 0090-6964/18/0200-0324/0 Ó 2017 Biomedical Engineering Society 324