Posture and the emergence of manual skills

In this paper, we examine how infants' natural manual and postural activities - what they prefer and do week by week -are related to developmental transitions in reaching skill and its neuromuscular control. Using a dense, longitudinal design, we tracked the manual and postural activities of four infants in a natural, free-play setting across the first year of life, and related these activities to two transitions in reaching as measured in a structured laboratory setting: the transition to reaching and the transition to stable reaching. Our data indicated that specific advances in the free-play setting preceded both transitions. Head and upper torso control, the ability to extend the arm and hand to a distant target, and the ability to touch and grasp objects placed nearby were all precursors to the onset of reaching, whereas sitting independently was associated with the transition to stable reaching. We also found important individual variability in when these 'components' were in place, indicating that it is the ensemble of components that is essential, not the order in which they develop or the timing of their contribution. These findings suggest that subsequent experimental manipulations should be planned with respect to infants' individual constellations of skills, rather than looking at only a single precursor to change.