EVIDENCE FOR A PHASE-TRANSITION IN THE EARLY DEVELOPMENT OF PREHENSION

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.