Speed of visual flow affects comfortable walking speed

When a person is instructed to walk at a comfortable speed, their actual walking speed is influenced by the velocity of visual flow that they experience. This is a surprising result, given that “walking comfortably” would seem to depend on purely biomechanical factors. To demonstrate this result, we utilized a computer controlled treadmill with a 6′ by 10′ walking surface, surrounded by three 8′ by 8′ projection screens oriented to provide an approximately 180 degree horizontal field of view. Users were able to walk at any speed of their choosing on the treadmill, with the speed of the treadmill belt automatically adjusting as needed. Ten subjects participated. Each subject had three minutes to gain familiarity with the user-controlled treadmill. Following this, each subject was directed to walk comfortably in three different conditions, visually slower (0.5X), visually same (1.0X) and visually faster (2.0X) than their walking speed. The practice and each of the three conditions on the treadmill were separated by five minutes of walking around in an actual hallway. The conditions were randomly ordered for each subject. Subjects on average chose 1.41 m/s for the visually slower condition, 1.21 m/s for the visually faster condition and 1.29 m/s for the visually same condition. This indicates that subjects use the speed of the visual flow when deciding their own comfortable walking speed. The result is consistent with a previous finding of ours, using the same treadmill but with the belt speed under computer control, that the speed at which walk/run and run/walk transitions occur is also affected by the speed of visual flow (Mohler et al., 2004, SIGGRAPH-APGV)