http://www.jneuroengrehab.com/content/10/1/80/abstract
Abstract (provisional)
Background
Individuals who have sustained a stroke can manifest altered locomotor steering behaviors
when exposed to optic flows expanding from different locations. Whether these alterations
persist in the presence of a visible goal and whether they can be explained by the
presence of a perceptuo-motor disorder remain unknown. The purpose of this study was
to compare stroke participants and healthy participants on their ability to control
heading while exposed to changing optic flows and target locations.
Methods
Ten participants with stroke (55.6 +/- 9.3 yrs) and ten healthy controls (57.0 +/-
11.5 yrs) participated in a mouse-driven steering task (perceptuo-motor task) while
seated and in a walking steering task. In the seated steering task, participants were
instructed to head or 'walk' toward a target in the virtual environment by using a
mouse while wearing a helmet-mounted display (HMD). In the walking task, participants
performed a similar steering task in the same virtual environment while walking overground
at their comfortable speed. For both experiments, the target and/or the focus of expansion
(FOE) of the optic flow shifted to the side (+/-20[degree sign]) or remained centered.
The main outcome measure was net heading errors (NHE). Secondary outcomes included
mediolateral displacement, horizontal head orientation, and onsets of heading and
head reorientation.
Results
In the walking steering task, the presence of FOE shifts modulated the extent and
timing of mediolateral displacement and head rotation changes, as well as NHE magnitudes.
Participants overshot and undershot their net heading, respectively, in response to
ipsilateral and contralateral FOE and target shifts. Stroke participants made larger
NHEs, especially when the FOE was shifted towards the non-paretic side. In the seated
steering task, similar NHEs were observed between stroke and healthy participants.
Conclusions
The findings highlight the fine coordination between rotational and translational
steering mechanisms in presence of targets and FOE shifts. The altered performance
of stroke participants in walking but not in the seated steering task suggests that
an altered perceptuo-motor processing of optic flow is not a main contributing factor
and that other stroke-related sensorimotor deficits are involved.
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