Flexibility in infant actions during arm- and leg-based learning in a mobile paradigm.

To understand young infants' flexible changes of learned actions when abrupt environmental changes occur, we examined fifty-four 3-month-olds who performed a mobile task, in which they learned to move the mobile by a string attached to their arms or legs (arm-based or leg-based learning). We manipulated the order of tests-arm to leg (AL) and leg to arm (LA)-and observed the time course of motion of four limbs. The infants in the AL condition showed a differentiated movement pattern, in which the movement of the connected arm was dominant, and when the connected limb changed, they immediately inhibited the prior movement pattern. The infants in the LA condition produced undifferentiated movement pattern of multiple limbs, which was maintained even when the critical limb was changed. The results suggest that the infants' flexibility of actions in a novel situation depends on the prior experience. We speculate neural mechanisms, which may underlie the difference between the arm-based and leg-based learning.