Optic flow in a virtual environment: sustained influence on speed of locomotion

Previous studies have shown that walking speeds can be modulated over short timescales by varying the rate of optic flow. This study investigated whether the modulating effect of optic flow on treadmill walking speed could be sustained for the longer time periods necessary for rehabilitation. An animated moving walkway was created in 3D Studio Max and rendered into a stereoscopic movie using Virtalis StereoWorks. The movie was projected (moving towards the subjects) onto a 5m wide screen in front of a self-paced treadmill. The movie was projected at three different speed conditions (0.75m/s, 1.5m/s and 3.0m/s) in counterbalanced order. Nine participants were instructed to maintain ‘comfortable walking speed’ throughout the 5 minute duration of each speed condition. A significant difference was found between the mean walking speeds of the participants at different animation speeds (ANOVA p<0.01); with lower animation speed associated with faster walking speeds and vice versa. This modulating effect was sustained for the duration of each 5-minute test, which suggests that it does have potential for use in rehabilitation and training. This study used healthy subjects, and further work is proposed to investigate the extent of this modulating effect on clinical groups.