Fig. 4.
Group averages of temporal parameters throughout experiment 1. Adaptation period is represented by shaded area. Arrows represent time correspondence between bar graphs and group average curves; the first arrow corresponds to the first epoch (baseline), and so forth. A: stride-by-stride time course of the temporal error (et) characterized by the double support difference. et follows the characteristic time course of a motor error: large values during early adaptation, error reduction as subjects adapt, and aftereffects during early deadaptation that are actively washed out. B: key epochs are shown for the error parameter double support difference. Abrupt transitions in et values are observed when the environmental conditions change (e.g., tied to split). This is indicated by the significant differences between baseline and early adaptation and those between late adaptation and early deadaptation. Also, subjects adapted as indicated by the significant decrease in et from early to late adaptation and stored these changes as shown by the aftereffects demonstrating the opposite asymmetry in early deadaptation. C: stride-by-stride time course of the temporal motor output (Tout). Tout follows the characteristic time course of motor outputs. Contrary to the temporal error time course, the temporal motor output smoothly changes from zero in baseline (tied) walking to values greater than zero during adaptation, and smoothly changes back to zero during deadaptation when the belts run in tied mode. D: key epochs are shown for Tout. Two important features characterizing the behavior of motor outputs are observed. First, there are smooth transitions between tied and split conditions as shown by the similarity in Tout values from baseline to early adaptation and from late adaptation to early deadaptation. Second, there is a statistical increase in Tout values from early to late adaptation. E: stride-by-stride time course of the alternate parameter to characterize temporal motor output (ToutA) based on toe-off timings. The time course of ToutA does not follow the characteristic time course of motor outputs. F: statistical analysis on key epochs of ToutA also shows that this parameter cannot be used to characterize the adaptation of temporal motor outputs. *Significant difference between epochs. NS, nonsignificant.