Anticipatory control of digit kinematics: a developmental milestone for motor skill acquisition.

During development, children naturally explore and manipulate objects with their hands and fingers, becoming more skillful with practice and with age. Adults grip objects strategically and adjust forces based on task demands; for example, digit positions on a glass of milk differ when transporting it versus when drinking from it. In these interactions, sensory feedback about digit position is crucial for precise control of the object. The brain forms distinct sensorimotor memories for both digit forces and positions, utilizing them to finely adjust grip parameters during skilled object manipulation. While the development of digit forces is well-studied, the development of anticipatory control of digit position remains less understood. This study investigated the development of anticipatory control of digit positions in children 5-7, 8-10, and 15-17 years during a dexterous manipulation task. A modified grip apparatus measured digit forces, positions, and object tilt (i.e., performance) at lift-off. A total of 39 children completed the study. Children aged 5-7 years failed to use sensorimotor memories about the object's hidden mass location from previous trials to plan their digit positions and digit forces. They applied an inaccurate torque that resulted in significant object tilt. Children aged 8-10 years showed a modest ability to use sensorimotor memories from previous trials when compared with the adolescent group. This study elucidates the ongoing development of dexterity into adolescence, offering insight into the maturation of sensorimotor capabilities throughout childhood and adolescence.