Effect of Optic Flow Speed on Step Initiation in Older and Younger Individuals

While walking humans perceive the environment as motionless despite the shift of the visual image on the retina. This perception of constancy is achieved through an interaction between gait pattern and the speed of optic flow. Several studies report an effect of artificially changing optic flow on gait parameters in younger individuals. Given the known decline in gait speed and slowing of postural reactions as people age, this effect may be different in older individuals. This hypothesis was tested by analyzing the latency of step initiation, peak velocity, step length, and movement time using a simulated virtual escalator moving at different speeds. The escalator was presented to 11 healthy older (77.1±8.9)and 11 healthy younger (21.9±1.6) participants via a Head Mounted Display (HMD). Participants took a single step forwards as soon as they detected escalator motion at one of six speeds ranging from 0.5 to 3 m/s, presented in random order. Participants also initiated a step in the physical world in response to a voiced command at their self-selected speed. All movements were recorded with Kinect sensing device for the Xbox 360. Results showed that older participants had significantly longer latency than younger across all speed conditions (p< 0.05). Increasing the escalator speed resulted in significantly decreased latency in both older (p<0.05) and younger participants (p<0.05).Peak velocity also increased significantly as speed increased (p<0.05). There was no significant difference between older and younger individuals in any parameters, except latency. The older participants responded to increased escalator speed in a manner similar to younger participants. This finding supports the feasibility of manipulating optic flow for facilitation of step initiation in older individuals.