Fig. 1

(A) Experimental paradigm. Participants engaged in three, randomly ordered experimental sessions, each involving a different learning condition. Experimental sessions included Reinforcement with pre-adaptation (purple), Reinforcement Alone (magenta), and the control condition of Adaptation Alone (green). Experimental blocks shown in white took place over ground and blocks shown in grey took place on the treadmill. All conditions involved: 2 min of baseline walking over ground, 2 min of baseline walking on the treadmill, 10 min of treadmill walking, 10 min of over ground training, and 10 min of over ground retention. During the Reinforcement with pre-adaptation condition, participants walked on a split-belt treadmill before engaging in over ground training that included reinforcement feedback. During the Reinforcement Alone condition, participants walked on a treadmill with tied-belts before over ground training that included reinforcement feedback. During the Adaptation Alone condition, participants walked on a split-belt treadmill and then walked over ground without reinforcement feedback. No reinforcement signaling/auditory feedback was provided during over ground retention for any of the conditions. (B) Illustration depicting the calculation of example step lengths. Step length was measured during periods of double support and was defined as the vector between right and left heel positions projected onto the direction of travel. In this example, the shorter step (blue) was taken by the right leg and the longer step (orange) was taken by the left leg. The metric of step length difference is agnostic to whether the right or left step is longer and is merely the difference between the step lengths of a pair of steps (SLD = short step length—long step length).