Jessica Berard, Joyce Fung and Anouk Lamontagne
A frequent consequence of stroke is locomotor disturbance. Locomotor steering, which relies heavily on the use of visual information, can be affected by a stroke but little is known about such disturbance. We investigated the ability of nine chronic stroke patients to steer in response to changes in the optic flow in a single-subject design. Subjects were instructed to walk straight for 5 m in a virtual environment with or without a perturbation of the focus of expansion (FOE), rotating horizontally 40° towards the right or left from the midline. Subjects exhibited 3 distinct behaviours: (I) 4/9 subjects showed no deficits in their locomotor strategy and responded by rotating their head and body in the direction opposite to the FOE shift, as previously reported in healthy individuals: (II) 2/9 subjects showed some degree of
steering adjustments in response to the flow but resulted in slightly higher net heading errors; (III) 3/9 showed large net heading errors that were especially pronounced when the FOE was rotated in the contralesional direction. The most important distinction between subjects who performed normally and those who had deficits was that the latter had a history of visuospatial neglect, suggesting that spatial neglect can have a persistent impact on visuomotor control. Our findings also suggest that standard pen-and-paper tests are not sufficient for detecting all forms of neglect and may adequately detect deficits in processing of dynamic visual motion or for stimuli located in far space.
