Figure 2.

Spatial and temporal parameters to quantify gait symmetry. A, Spatial symmetry was quantified by the normalized difference in step lengths. Figurines were made from kinematic data of two consecutive steps during catch trial of a sample subject. Spatial aftereffects are illustrated by the difference in step lengths when the right leg (gray) is leading versus when the left leg is leading (black). B, Temporal symmetry was quantified by the phase shift (lag) producing the largest cross-correlation between the right and left limb angles. Behavior during baseline is shown. Limb angle is defined as the angle between the limb axis (line from hip to ankle marker) and the vertical axis, as shown on the axis drawn on the top-left figurine. Example of limb angle trajectories as a function of time are shown at the bottom-left (gray and black oscillatory traces at the bottom). Top-right panel indicates the cross-correlation values as a function of lag for the cycles shown on the left. During baseline, legs move in anti-phase; consequently a lag of 0.5 leads to the maximal cross-correlation value.