Posture becomes integrated with other goal-directed behaviors early in infancy and continues to develop into the second decade of life. However, the developmental time course over which posture is stabilized relative to the base of support during a dynamic manual precision task has not been examined. Postural-manual integration was assessed in 7-year-olds, 10-year-olds, and adults using a postural-manual task in which task precision (target fitting size) and postural difficulty (reaching distance to a target) were manipulated. The main dependent variable was postural time-to-contact (TtC). Results indicated systematic age effects in which TtC was shortest in the 7-year-olds, increased in the 10-year-olds, and was longest in the adults. Across all age levels, TtC was longer when performing a precision ft compared with a nonprecision ft and when fitting at a near target compared with fitting at a far target. Finally, TtC increased over the course of the manual fitting task, suggesting that posture became increasingly stable as the hand approached the opening. The ability to modulate postural TtC during the course of the fitting trial was most pronounced in adults as compared with both groups of children. These results suggest that even by 10-years of age, children are not yet able to fully integrate postural movements with goal directed manual tasks at adult-like levels.
Haddad and Claxton are with the Dept. of Health and Kinesiology, Purdue University, West Lafayette, IN. Haddad is also with the Center for Aging and the Life Course, Purdue University, West Lafayette, IN. Melzer is with the Dept. of Psychology, Sacred Heart University, Fairfield, CT. Hamill and van Emmerik are with the Dept. of Kinesiology, University of Massachusetts, Amherst, MA.