Article

In adults, locomotor movements are accommodated to various support surface
conditions by means of specific anticipatory locomotor adjustments and changes in
the intersegmental coordination. Here we studied the kinematic strategies of
toddlers at the onset of independent walking when negotiating various support
surface conditions: stepping over an obstacle, walking on an inclined surface,
and on a staircase. Generally, toddlers could perform these tasks only when
supported by the arm. They exhibited strategies very different from those of the
adults. Although adults maintained walking speed roughly constant, toddlers
markedly accelerated when walking downhill or downstairs and decelerated when
walking uphill or upstairs.
Their coordination pattern of thigh-shank-foot
elevation angles exhibited greater inter-trial variability than that in adults,
but it did not undergo the systematic change as a function of task that was
present in adults. Thus the intersegmental covariance plane rotated across tasks
in adults, whereas its orientation remained roughly constant in toddlers. In
contrast with the adults, the toddlers often tended to place the foot onto the
obstacle or across the edges of the stairs. We interpret such foot placements as
part of a haptic exploratory repertoire and we argue that the maintenance of a
roughly constant planar covariance--irrespective of the surface inclination and
height--may be functional to the exploratory behavior.
The latter notion is
consistent with the hypothesis proposed decades ago by Bernstein that, when
humans start to learn a skill, they may restrict the number of degrees of freedom
to reduce the size of the search space and simplify the coordination.

Langue : ANGLAIS

Tiré à part : OUI