This article is part of the series Select Papers from the 2006 International Workshop on Virtual Reality in Rehabilitation, edited by Emily A Keshner, Patrice (Tamar) Weiss.

Research

Modulation of walking speed by changing optic flow in persons with stroke

Anouk Lamontagne¹ , Joyce Fung¹ , Bradford J McFadyen² and Jocelyn Faubert³

¹  School of Physical and Occupational Therapy, McGill University and Jewish Rehabilitation Hospital Research Center (CRIR), Montreal, Canada

²  Department of Rehabilitation, Laval University, and Quebec Rehabilitation Research Institute (CIRRIS), Quebec, Canada

³  Vision and Perception Laboratory, School of Optometry, University of Montreal, Montreal, Canada

author email corresponding author email

Journal of NeuroEngineering and Rehabilitation 2007, 4:22doi:10.1186/1743-0003-4-22

Published:	26 June 2007

Abstract

Background

Walking speed, which is often reduced after stroke, can be influenced by the perception of optic flow (OF) speed. The present study aims to: 1) compare the modulation of walking speed in response to OF speed changes between persons with stroke and healthy controls and 2) investigate whether virtual environments (VE) manipulating OF speed can be used to promote volitional changes in walking speed post stroke.

Methods

Twelve persons with stroke and 12 healthy individuals walked on a self-paced treadmill while viewing a virtual corridor in a helmet-mounted display. Two experiments were carried out on the same day. In experiment 1, the speed of an expanding OF was varied sinusoidally at 0.017 Hz (sine duration = 60 s), from 0 to 2 times the subject's comfortable walking speed, for a total duration of 5 minutes. In experiment 2, subjects were exposed to expanding OFs at discrete speeds that ranged from 0.25 to 2 times their comfortable speed. Each test trial was paired with a control trial performed at comfortable speed with matching OF. For each of the test trials, subjects were instructed to walk the distance within the same time as during the immediately preceding control trial. VEs were controlled by the CAREN-2 system (Motek). Instantaneous changes in gait speed (experiment 1) and the ratio of speed changes in the test trial over the control trial (experiment 2) were contrasted between the two groups of subjects.

Results

When OF speed was changing continuously (experiment 1), an out-of-phase modulation was observed in the gait speed of healthy subjects, such that slower OFs induced faster walking speeds, and vice versa. Persons with stroke displayed weaker (p < 0.05, T-test) correlation coefficients between gait speed and OF speed, due to less pronounced changes and an altered phasing of gait speed modulation. When OF speed was manipulated discretely (experiment 2), a negative linear relationship was generally observed between the test-control ratio of gait speed and OF speed in healthy and stroke individuals. The slope of this relationship was similar between the stroke and healthy groups (p > 0.05, T-test).

Conclusion

Stroke affects the modulation of gait speed in response to changes in the perception of movement through different OF speeds. Nevertheless, the preservation of even a modest modulation enabled the persons with stroke to increase walking speed when presented with slower OFs. Manipulation of OF speed using virtual reality technology could be implemented in a gait rehabilitation intervention to promote faster walking speeds after stroke.