The effect of virtual visual scene inclination transitions on gait modulation in healthy older versus young adults-A virtual reality study

Bipedal locomotion requires body adaptation to maintain stability after encountering a transition to incline walking. A major part of this adaptation is reflected by adjusting walking speed. When transitioning to uphill walking, people exert more energy to counteract gravitational forces pulling them backward, while when transitioning to downhill walking people break to avoid uncontrolled acceleration. These behaviors are affected by body-based (proprioception and vestibular) cues as well as by visual cues. Since older age adversely affects walking, it is unclear whether older adults rely on vision during locomotion in a similar manner to younger individuals. In this study, we tested whether the influence of visual cues on these walking speed modulations in healthy older adults (60-75 years old, N = 15) were comparable to those found in healthy young adults (20-40 years old, N = 12). Using a fully immersive virtual-reality system embedded with a self-paced treadmill and projected visual scene, we manipulated the inclinations of both the treadmill and the visual scene in an independent manner, and measured participants walking speed. In addition, we also measured individual visual field dependency using the rod and frame test. The older adults presented the expected braking (decelerating) and exertion (accelerating) effects, in response to downhill and uphill visual illusions, respectively, in a similar manner to the young group. Furthermore, we found a significant correlation between the magnitude of walking speed modulation and visual field dependency in each of the groups with significantly higher visual field dependency in older adults. These results suggest that with aging individuals maintain their reliance on the visual system to modulate their gait in accordance with surface inclination in a manner similar to that of younger adults.