Anticipatory Control of Digit Kinematics
Description
This study investigated the development of anticipatory control of digit positions in children 5-7, 8-10, and 15-17 years (Groups 1, 2, 3) 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. Outputs are provided across 10 trials in 3 different conditions (Left, Right, Center). The data were run through a 5th order low pass Butterworth filter. Force and object roll data were used to compute Tcom, Peak roll, dy (vertical distance between contact points), dLF (difference in load forces), and GF (average grip force). The adolescents modulated their digit placement depending on CM condition similar to young adults, as evidenced by Tcom matching the required external torque and peak roll reducing within several trials, and an adult-like strategy of creating a digit separation (dy) for mechanical advantage. Group 1 began their trials with a higher thumb with minimal change in digit position (dy) across the 10 trials. This group failed to concurrently distribute the load forces (dLF) between their index finger and thumb to apply more load force at the thumb in relation to the index finger. Similarly, Group 2 showed a small change in digit placement across the trials with minimal or no compensation in the load force distribution between the thumb and index finger, although they were successful in one of the 3 conditions. Adolescents, like adults, used implicit learning to anticipate digit force in parallel with digit positions. However, in children 5-7 years old, implicit learning for anticipatory digit position modulation did not occur. For children 8-10yrs, this learning was only observed in the LCM condition and not to the extent that allowed success in minimizing object roll. Our results suggest a separate, more prolonged timeline for the development of anticipatory mechanisms of digit kinematics than for digit kinetics in children.