The development toward stereotypic arm kinematics during reaching
in the first 3 years of life
Experimental Brain Research, (1997)Abstract
We recorded reaching movements from nine
infants longitudinally from the onset of reaching (5th
postnatal month) up to the age of 3 years. Here we analyze
hand and proximal joint trajectories and examine
the emerging temporal coordination between arm segments.
The present investigation seeks (a) to determine
when infants acquire consistent, adult-like patterns of
multijoint coordination within that 3-year period, and
(b) to relate their hand trajectory formation to underlying
patterns of proximal joint motion (shoulder, elbow). Our
results show: First, most kinematic parameters do not assume
adult-like levels before the age of 2 years. At this
time, 75% of the trials reveal a single peaked velocity
profile of the hand. Between the 2nd and 3rd year of life,
ªimprovementsº of hand- or joint-related movement units
are only marginal. Second, infant motor systems strive to
obtain velocity patterns with as few force reversals as possible
(uni- or bimodal) at all three limb segments. Third,
the formation of a consistent interjoint synergy between
shoulder and elbow motion is not achieved within the
1st year of life. Stable patterns of temporal coordination
across arm segments begin to emerge at 12±15 months
of age and continue to develop up to the 3rd year. In summary,
the development toward adult forms of multijoint
coordination in goal-directed reaching requires more time
than previously assumed. Although infants reliably grasp
for objects within their workspace 3±4 months after the onset of reaching,
stereotypic kinematic motor patterns are not expressed before the
2nd year of life.
Description
diverse cognitive systems bib