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

Bipedal locomotion requires body adaptation to maintain stability after encountering a transition to inclined walking. A major adaptation is the change in walking speed to maintain optimal energy consumption. 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. This behavior is controlled by three main senses: proprioception and vestibular (aka body-based cues), and visual cues. In this study, we aimed to measure the influence of the visual cues on these modulations in healthy older adults and compare it to healthy young adults. To that end, we used a fully immersive virtual-reality system embedded with a self-paced treadmill and projected visual scene that allowed us to manipulate the inclinations of the treadmill and the visual scene in an independent manner. In addition, we measured the visual field dependency of each participant using the rod and frame test. The group of older adults presented the braking (decelerating), and exertion (accelerating) effects, in response to downhill and uphill visual illusions, respectively, in a similar manner as the young group. Furthermore, we found a significant correlation between the intensity of the speed modulation and the visual field dependency for each group separately, however the visual field dependency was significantly higher in the elderly 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 the same manner as young adults.