Oxford Journals: The Journal of Gerontology: Medical Sciences
Abstract
Background. Rapid stepping reactions are a prevalent response to sudden loss of balance and are thought to play
a crucial role in preventing falls. Previous dual-task studies, involving concurrent performance of step reactions and
a visuomotor tracking task, indicated that online visual attention was not required to guide the step, even when nearby
objects increased demands for accurate foot movement. However, the planning and execution of the step apparently
required attentional resources initially allotted to the tracking task. Reallocation of these resources (‘‘attention switching’’)
was delayed in older adults. The present study examined the influence of the competition for attentional resources by
comparing trials performed with and without the concurrent task.
Methods. Unpredictable platform perturbations were used to evoke rapid forward stepping reactions in healthy young
and older adults. Challenging obstacles and/or step targets increased demands for accurate foot motion in some trials.
A concurrent tracking task was performed in half of the trials.
Results. Although participants looked down more frequently in the absence of the tracking task, the ability to clear the
obstacle or land on the step target and other spatiotemporal features of the stepping reactions were largely unaffected.
There was, however, one notable exception: In older adults, the duration and amplitude of the ‘‘anticipatory postural
adjustment’’ that preceded foot lift were reduced in tracking trials, resulting in increased lateral center-of-mass motion.
Conclusion. Impaired attention switching apparently compromised the control of lateral stability during stepping
reactions in older adults, and may be an important contributor to increased risk of falling.This study was supported by an operating grant (MOP-13355) from the
Canadian Institutes of Health Research (CIHR). B.E.M. was a CIHR Senior
Investigator, and W.E.M. held a Canada Research Chair in Neurorehabilitation.
J.L.Z. held scholarships from the Natural Sciences and
Engineering Research Council and the Ontario Neurotrauma Foundation