A longitudinal study was conducted to examine the hypothesis that the
development of prehension during the first 5 months of life is charact
erized by the presence of a discontinuous phase transition. Ten infant
s were observed weekly from 8 to 24 weeks of age. Video recordings wer
e made of movements toward an attractive object which were classified
according to two behavioral categories: reaching without grasping and
reaching with grasping. The time evolution of the relative incidence o
f these behavioral categories was analyzed statistically. Evidence was
found for a sudden jump from a (developmental) state in which reachin
g without grasping is predominant to a state in which reaching with gr
asping is predominant. Evidence was also found for bimodality, inacces
sibility, and anomalous variance. In combination, these findings suppo
rt the hypothesis that the investigated behavioral change constitutes
a discontinuous phase transition. The behavioral change in question oc
cur-led at the moment in developmental time at which the attractor str
ength of leaching for objects as such relative to that of other behavi
oral activities appeared to be inn-eased. (C) 1998 John Wiley & Sons,
Inc.