Modulation of Walking Speed by Changing Optic Flow in Persons with Stroke

The present study was undertaken to compare the modulation of walking speed in response to optic flow (OF) speed changes between persons with stroke and healthy controls. Twelve individuals with stroke and 12 healthy controls walked on a self-paced treadmill viewing a virtual corridor in a helmet-mounted display. In experiment 1, the speed of an expanding OF was varied sinusoidally at 0.017Hz, from 0 to 2 times the individual´s comfortable walking speed. In experiment 2, individuals were instructed to walk through a virtual hallway of 10m at their comfortable pace (control trials). During the test trials that followed the control trials, expanding optic flows ranging from 0.25 to 1.75 of the initial comfortable speed were randomly presented. Subjects were instructed to walk the test trial distance within the same time as during the preceding control trial. Results from experiment 1 showed that gait speed was modulated out-of-phase with respect to OF speed in the healthy controls, but it varied from out-of-phase to in-phase patterns in the individuals with stroke. A negative linear relationship was observed between gait speed and OF speed in healthy and stroke individuals in experiment 2. These results indicate that individuals with stroke, although able to modulate the gait speed by changing the perception of movement through different OF speeds, present with altered modulation response patterns as compared to healthy subjects