| The control of posture and reaching in early childhood have been studied extensively as separate phenomena. Furthermore most studies of motor development have used age as an external marker of developmental milestones. An alternative to age dependent designs has been proposed by Campos and Bertenthal (1989), where onset of self-produced locomotion serves as a predictor for cognitive and socio-emotional development. The present study investigated how different amounts of standing experience influences the coordination of posture and reaching in eight month old infants. Two groups of infants were studied based on the length of time that they had been standing independently (experienced standers at least one month; inexperienced standers no more than 5–10 days). Infants were videotaped using an overhead view at 30 frames per sec, while reaching for a peg placed at near, middle and far distance (1/3, 3/3 and 4/3 arm length) in a sitting and standing position. Kinematic analysis of the metacarpophalangeal joint was used to quantify the reach and a head marker was used as an indicator of postural control.; Results suggest that eight month old infants divide their reach into three distinct phases: (1) initiation phase, (2) transport phase, (3) homing phase. During the initiation phase, inexperienced standers demonstrated a significantly greater postural adjustment as expressed by a larger head displacement than the experienced standers (p = 0.05). This finding supports the hypothesis that inexperienced standers use a different pattern of coordination between the trunk and the arm movement than the experienced standers.; Curvelinearity of the hand path decreased with increasing target distance for both groups of infants. The curvelinearity of the reach therefore appears to be affected by the systematic variation of target distance, suggesting that the straightness of the reach increases as task constraints increase.; In conclusion, the results of the present study demonstrate that eight month old infants tend to bring their hand to objects in the environment as a whole body engagement. This whole body engagement necessitates the integration of postural and reaching components into one action system. In addition, these findings support the interdependency between posture and reaching and provide evidence that the development of the integration of postural and limb control is influenced by the interaction of the child with its environment rather than by age alone. |
