Thinking about walking: effects of conscious correction versus distraction on locomotor adaptation

Abstract

Control of the human walking pattern normally requires little thought, with conscious control used only in the face of a challenging environment or a perturbation. We have previously shown that people can adapt spatial and temporal aspects of walking to a sustained perturbation generated by a split-belt treadmill. Here we tested whether conscious correction of walking, versus distraction from it, modifies adaptation. Conscious correction of stepping may expedite the adaptive process and help to form a new walking pattern. However, because walking is normally an automatic process, it is possible that conscious effort could interfere with adaptation, whereas distraction might improve it by removing competing voluntary control. Three groups of subjects were studied: a control group was given no specific instructions, a conscious correction group was instructed how to step and given intermittent visual feedback of stepping during adaptation, and a distraction group performed a dual-task during adaptation. After adaptation, retention of aftereffects was assessed in all groups during normal treadmill walking without conscious effort, feedback, or distraction. We found that conscious correction speeds adaptation, whereas distraction slows it. Subjects trained with distraction retained aftereffects longest, suggesting that the training used during adaptation predicts the time course of deadaptation. An unexpected finding was that these manipulations affected the adaptation rate of spatial but not temporal elements of walking. Thus conscious processes can preferentially access the spatial walking pattern. It may be that spatial and temporal controls of locomotion are accessible through distinct neural circuits, with the former being most sensitive to conscious effort or distraction.

Fig. 1.

A: diagram of marker location and limb angle convention. B: experimental paradigm showing the periods of split-belt walking and conditions.

Fig. 2.

A: limb angle trajectories plotted as a function of time in early split-belt adaptation—2 cycles are shown. Positive limb angles are when the limb is in front of the trunk (flexion). Two time points are marked—slow heel strike (HS) in black and fast HS in gray. The spread between the limb angles is directly proportional to the step lengths shown in B. Step lengths can be changed through alterations in phasing (lag time at peak cross-correlation) or through a shift in the center of oscillation (midpoint angle of the limb between heel strike and toe off for each leg). B: stick figure diagram of the legs taking 2 consecutive steps. C: step lengths can be equalized through a shift in the center of oscillation (purely spatial change). Gray trajectory represents the slow limb in early adaptation. A spatial shift in the slow limb's center of oscillation can result in equal step lengths. D: a phase lag (purely temporal change) in the fast limb from the gray trajectory (early adaptation) to the black trajectory will also equalize the step lengths.

Fig. 3.

A: example of single subject (control) step symmetry data for the entire experiment. In baseline and deadaptation periods, the belts were tied (same speed). In the adaptation block, belts were split (3:1 speed ratio). The visual feedback and dual-task conditions were only used during the adaptation block. B: subjects did not differ in step symmetry during periods of early adaptation (P = 0.27), late adaptation (P = 0.96), early deadaptation (P = 0.83), and late deadaptation (P = 0.52).

Fig. 4.

Adaptation and deadaptation curves for step symmetry. A: average adaptation curves for the 3 groups, with SE indicated by the shaded area. Baseline values are subtracted out from curves (i.e., symmetry is indicated by a value of 0). B: average deadaptation curves for the 3 groups. Recall that all groups deadapted under the same condition (no feedback or distraction). Curves are shown individually to more clearly show the plateau level.

Fig. 5.

The adaptation and deadaptation rate expressed as the number of strides until a plateau is reached for each measure. A: for step symmetry, distraction subjects adapted slower than control and conscious correction subjects. Whereas conscious correction subjects tended to adapt faster than control subjects, this difference did not reach significance. B: for deadaptation, distraction subjects also took longer to reach a plateau than the control and conscious correction subjects. The rate of deadaptation was similar for conscious correction and control subjects. C: similar trends are shown for rate of adaptation in center of oscillation difference, compared with step symmetry. Distraction subjects took the longest to adapt vs. control subjects and conscious correction. D: deadaptation in center of oscillation difference is similar to adaptation. The conscious correction group adapted fastest, then control, and distraction was the slowest. E: all groups adapted phasing at similar rates. F: deadaptation rate for phasing was also similar across groups.

Fig. 6.

Adaptation and deadaptation curves for the center of oscillation difference. A: average adaptation curves for the 3 groups plotted as in Fig. 4. Trends seen in the center of oscillation are comparable to those seen in step symmetry. B: average deadaptation curves, shown individually.

Fig. 7.

Adaptation and deadaptation curves for phasing. A: average curves for the 3 groups plotted as in Fig. 4. No differences were found in the adaptation rate. B: average deadaptation curves shown individually. Again, no differences were found in phasing deadaptation rate.