10 research outputs found
Stepping to recover balance in complex environments: is online visual control of the foot motion necessary or sufficient?
Rapid step reactions evoked by balance perturbation must accommodate constraints on limb motion
imposed by obstacles and other environmental features. Recent results suggest that the required visuospatial
information (VSI) is acquired and stored “proactively”, prior to perturbation onset (PO); however,
the extent to which “online” (post-PO) visual feedback can contribute is not known. To study this, we
used large unpredictable platform perturbations to evoke rapid step reactions, while subjects wore liquid
crystal goggles that occluded vision: (1) prior to PO (forcing use of online-VSI), (2) after PO (forcing use of
stored-VSI), or (3) not at all (normal-VSI). Subjects stood behind a barrier in which the location of a narrow
slot, through which the foot had to be moved during forward step reactions, was varied unpredictably
between trials. Within subjects who were able to do the task (6 of 8 young adults tested), responses in
stored-VSI and normal-VSI trials were very similar. However, in online-VSI trials, the foot-off time for the
step through the slot was delayed (by ∼50 ms, on average). Presumably, this delay allowed more time to
acquire and process online-VSI regarding the required foot trajectory, yet subjectswere still more likely to
select the “wrong” foot (contralateral to the slot location) and to contact the barrier while moving the foot
through the slot, in online-VSI trials. These results suggest a critical role for stored-VSI during the earliest
phase of the step, in selecting the step limb and planning the initial trajectory. Online acquisition and
processing of the required VSI may be too slow to allow effective control of this early phase, particularly
in situations where the demands for accurate foot motion are high.This study was supported by an operating grant (#MOP-13355)
from the Canadian Institutes of Health Research (CIHR)
Gaze behavior governing balance recovery in an unfamiliar and complex environment
Visuospatial information regarding obstacles and other environmental constraints on limb movement is essential for the successful planning
and execution of stepping movements. Visuospatial control strategies used during gait and volitional stepping have been studied extensively;
however, the visuospatial strategies that are used when stepping rapidly to recover balance in response to sudden postural perturbation are not well
established. To study this, rapid forward stepping reactions were evoked by unpredictable support-surface acceleration while subjects stood amid
multiple obstacles that moved intermittently and unpredictably prior to perturbation onset (PO). To prevent predictive control, subjects performed
only one trial (their very first exposure to the perturbation and environment). Visual scanning of the obstacles and surroundings occurred prior to
PO in all subjects; however, gaze was never redirected at the obstacles, step foot or landing site in response to the perturbation. Surprisingly, the
point of gaze at time of foot-contact was consistently and substantially anterior to the step-landing site. Despite the apparent absence of 'online' visual feedback related to the foot movement, the compensatory step avoided obstacle contact in 10 of 12 young adults and 9 of 10 older subjects.
The results indicate that the balance-recovery reaction was typically modulated on the basis of visuospatial environmental information that was
acquired and continually updated prior to perturbation, as opposed to a strategy based on 'online' visual control. The capacity to do this was not
adversely affected by aging, despite a tendency for older subjects to look downward less frequently than young adults.Supported by the Canadian Institutes of Health Research and
the Ontario Neurotrauma Foundation
The Press, Volume 10, Issue 11, November 15, 1973
The Press, Volume 10, Issue 11 includes: Scientists are cloning frogs and this is causing some public paranoia regarding the impact of the individuality of identity; Does the individual count in our democratic system?; Additions to the University Programme with extra funds
The Press, Volume 10, Issue 16, January 10, 1974
The Press, Volume 10, Issue 16 includes: John Isaac appointed as BUSAC vice-president and is likely to bring change to student politics; Conversation about having buses run from the Pen Centre up to Brock on a Sunday
The Press, Volume 10, Issue 18, January 24, 1974
The Press, Volume 10, Issue 18 includes: Article about Jesse Stoner being a fascist; Union meeting called to discuss the “non-reappointment” of 16 faculty and rising and tuition costs