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Altered steering strategies for goal-directed locomotion in stroke.

Aburub AS, Lamontagne A - J Neuroeng Rehabil (2013)

Bottom Line: The main outcome measure was net heading errors (NHE).Secondary outcomes included mediolateral displacement, horizontal head orientation, and onsets of heading and head reorientation.The findings highlight the fine coordination between rotational and translational steering mechanisms in presence of targets and FOE shifts.

View Article: PubMed Central - HTML - PubMed

ABSTRACT

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°) 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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Related in: MedlinePlus

This figure shows box and whisker plots of medio-lateral displacements (left panel) and head reorientation (right panel) across target and FOE locations for the healthy (A) and stroke (B) participants. The body of the boxes represents the first and third quartile while the middle horizontal line and open squares within the boxes represent, respectively, the median and mean of the data set. The whiskers extend from the lowest to the highest values of the data set.
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Figure 3: This figure shows box and whisker plots of medio-lateral displacements (left panel) and head reorientation (right panel) across target and FOE locations for the healthy (A) and stroke (B) participants. The body of the boxes represents the first and third quartile while the middle horizontal line and open squares within the boxes represent, respectively, the median and mean of the data set. The whiskers extend from the lowest to the highest values of the data set.

Mentions: Figure 3 shows CoM ML displacement and head orientation in the virtual world coordinates for all stroke and healthy control participants. In both groups, a clear effect of target and FOE location on the extent of ML displacement and head reorientation was observed. First, the virtual ML displacement and, in most instances, virtual head reorientation, occurred in the direction of the target shift. The direction of the FOE shifts, however, modulated the extent of these adjustments. For example, when the target and FOE were shifted in the same direction (ipsilateral shifts), participants were being ‘pulled’ toward the FOE and ended up facing the target located 2 m to the side. This led to large virtual ML displacements towards the direction of the target, with little head reorientation needed to be aligned perfectly with the target. In contrast, when the FOE was shifted contralaterally to the target shift, participants were ‘pulled’ away from the target, leading to small virtual ML adjustments that were compensated by large head reorientations. When the flow remained centered, targets shifts resulted in ML deviations and head reorientations towards the target, which amplitudes were in between that of the ispsi- and contralateral conditions.


Altered steering strategies for goal-directed locomotion in stroke.

Aburub AS, Lamontagne A - J Neuroeng Rehabil (2013)

This figure shows box and whisker plots of medio-lateral displacements (left panel) and head reorientation (right panel) across target and FOE locations for the healthy (A) and stroke (B) participants. The body of the boxes represents the first and third quartile while the middle horizontal line and open squares within the boxes represent, respectively, the median and mean of the data set. The whiskers extend from the lowest to the highest values of the data set.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3733933&req=5

Figure 3: This figure shows box and whisker plots of medio-lateral displacements (left panel) and head reorientation (right panel) across target and FOE locations for the healthy (A) and stroke (B) participants. The body of the boxes represents the first and third quartile while the middle horizontal line and open squares within the boxes represent, respectively, the median and mean of the data set. The whiskers extend from the lowest to the highest values of the data set.
Mentions: Figure 3 shows CoM ML displacement and head orientation in the virtual world coordinates for all stroke and healthy control participants. In both groups, a clear effect of target and FOE location on the extent of ML displacement and head reorientation was observed. First, the virtual ML displacement and, in most instances, virtual head reorientation, occurred in the direction of the target shift. The direction of the FOE shifts, however, modulated the extent of these adjustments. For example, when the target and FOE were shifted in the same direction (ipsilateral shifts), participants were being ‘pulled’ toward the FOE and ended up facing the target located 2 m to the side. This led to large virtual ML displacements towards the direction of the target, with little head reorientation needed to be aligned perfectly with the target. In contrast, when the FOE was shifted contralaterally to the target shift, participants were ‘pulled’ away from the target, leading to small virtual ML adjustments that were compensated by large head reorientations. When the flow remained centered, targets shifts resulted in ML deviations and head reorientations towards the target, which amplitudes were in between that of the ispsi- and contralateral conditions.

Bottom Line: The main outcome measure was net heading errors (NHE).Secondary outcomes included mediolateral displacement, horizontal head orientation, and onsets of heading and head reorientation.The findings highlight the fine coordination between rotational and translational steering mechanisms in presence of targets and FOE shifts.

View Article: PubMed Central - HTML - PubMed

ABSTRACT

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°) 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.

Show MeSH
Related in: MedlinePlus