Fig 1.
a) Subjects’ lateral movements (red arrows) controlled the lateral position of a real-time Visual Feedback Marker (black sphere). All trials began after subjects positioned the Visual Feedback Marker within the baseline lane shown in green. A progress bar timer then displayed a 5 second countdown and subjects were given visual instructions to “Get ready”. When time expired, the on-screen instructions changed to “GO,” and subjects maneuvered as quickly as possible to a target lane shown in grey. b) Straight. The target was within the baseline lane. Subjects did not maneuver. c) Known. A target was displayed to the either the left or right of the baseline lane during the 5 second countdown. At “GO,” subjects maneuvered to the target. d) Unknown. Targets were displayed simultaneously to both the left and right of the baseline lane. At “GO,” one of the targets disappeared, indicating that subjects should maneuver immediately to the remaining target.
Fig 2.
Representative data from a single subject of center of mass (COM) and left and right base of support (BOS) position before and after the “GO” signal during each condition. a) Straight. “cL” and “cR” denote control left and right steps used for analysis. b) Known left. “n” denotes the maneuver step. The four steps prior to the n step, the n-1 through n-4 steps, were analyzed for specific anticipatory behavior. c) Unknown left. For this condition only, the “GO” signal denotes when subjects learned the maneuver direction. The two steps initiated prior to the “GO” signal, the go-1 and go-2 steps, were analyzed for general anticipatory behavior. The “n” or maneuver step is also shown for reference. d) Determination of step width (SW), and step length (SL) for the n-1 step of a Known left example trial. Step width for the n-1 step was calculated as the medio-lateral distance between the two 5th Metatarsal markers at the n-1 initial contact. Step length for the n-1 step was calculated as the fore-aft distance between the two 5th Metatarsal markers at the n-1 initial contact. e) Determination of step time (ST). Step time for the n-1 step was calculated as the time between the n-1 and n step initial contact events.
Table 1.
Means and standard deviations for Known condition.
Table 2.
Known target direction statistical analysis.
Fig 3.
Example margin of stability data for one subject during a) a Known left trial and b) an Unknown left trial. Left (L) and Right (R) minimum margin of stability (MOS), denoted by “x” marker at each step, is the minimum distance between the base of support (BOS) and extrapolated center of mass (XCOM). c) Minimum margin of stability, Known condition. The minimum margin of stability was significantly larger for the n-4 through n-2 steps, and significantly smaller one step prior to the maneuver, the n-1 step (ipsilateral to the target), compared to the control step. d) Minimum margin of stability, Unknown condition. Minimum margin of stability was significantly larger 2 steps before the “GO” signal, the go-2 step. (*)Step is significantly different (p< 0.05) from control. For c) and d) the Box plots are collapsed across limb side to show main effect of step. Each box represents 14 data subjects’ data.
Fig 4.
Step Width, Step Length, and Step Time.
Each box plot is collapsed across limb side to show main effect of step on step width, step length and step time. Each box represents 14 subjects’ data. a) Step width, Known condition. The n-2 step width was significantly larger than the control step (contralateral to the target). b) Step width, Unknown condition. Step width was significantly increased for both steps immediately preceding the “GO” signal compared to the control step. c) Step length, Known condition. There was a significant effect of step on step length, but no pairwise comparisons vs. the control step were significant. d) Step length, Unknown condition. There were no significant effects of step on step length. e) Step time, Known condition. Compared to the control step, step time was significantly shorter during the n-1 step. f) Step time, Unknown condition. There was a significant effect of step on step time, but neither the go-2 or go-1 steps were significantly different from the control step. (*)Step is significantly different (p<0.05) from control.
Fig 5.
Example hip joint angle data for one subject comparing a Straight trial vs. a) a Known left trial and b) an Unknown trial. c, d) Each box plot is collapsed across limb side to show main effect of step on peak stance phase hip extension angle. Each box represents 12 subjects’ data (two subjects excluded). c) Known. The hip was significantly more flexed at the n-1 step compared to the control step. d) Unknown. The hip was significantly more flexed at both steps immediately preceding the “GO” signal compared to the control step. (*)Step is significantly different (p<0.05) from control.
Fig 6.
Example knee joint angle data for one subject comparing a Straight trial vs. a) a Known right trial and b) an Unknown trial. c, d) Each box plot is collapsed across limb side to show main effect of step on peak stance phase knee extension angle. Each box represents 14 subjects’ data. c) Known. The knee was significantly more flexed at the n-1 step compared to the control step. d) Unknown. There was a significant effect of step on peak knee extension angle, but pairwise comparisons vs. the control step were not significant. (*)Step is significantly different (p<0.05) from control.
Table 3.
Means and standard deviations for Unknown condition.
Table 4.
Unknown target direction statistical analysis.