Influência de restrições intrínsecas e extrínsecas no alcance manual de lactentes.

Abstract

The aim of the current research was to examine the influence of intrinsic and extrinsic constraints on reaching movements in 4-6-month-old infants. Age, level of skill and experience gained by spontaneous practice of reaching were the intrinsic constraints analyzed. The relationship between muscular torque required for reaching and gravitational torque was the extrinsic constraint, which was manipulated by different body orientations. Kinematical and qualitative variables for movements performed in supine, reclined and seated positions were analyzed in three different studies in order to verify how constraints affect young infants reaching. The results indicate that body orientation affected reaching behavior in 4- month-old infants. However, when considering the level of skill rather than age, body orientation was shown to affect reaching behavior during its emergence only in less-skilled reachers. The level of skill is thus suggested to be a more relevant constraint than age in the acquisition of reaching. Temporal and spatio-temporal parameters of reaching were more sensitive to constraints imposed by body orientation, age and level of skill. Seated position elicited both reaching in less-skilled reachers during the behavior acquisition and grasping in more-skilled reachers after spontaneous practice. These findings suggest that level of skill, experience in reaching, and body orientation may affect reaching behavior in young infants. These constraints should therefore be taken into account when examining the development of infant reaching. This work supports the idea that the confluence of constraints determines the young infants action and that a change in this confluence can eventuate in a change in action.