PMC

Visual feedback was accomplished by displaying trunk posture (graph on right) and lumbar curvature (bars on left) in a display similar to that illustrated here. Trunk posture was represented on an x-y graph, with the x-axis as twist and the y-axis as flexion. Subjects matched a circle (representing their position) to a square (representing the target). For lumbar curvature, subjects matched the right bar plot (representing their lumbar curvature) with the left bar plot (representing the target). The lumbar curvature display was turned off for reposition sense testing.

Directional reposition sense errors (dRSE), representing the directional bias in position targeting, were small (means with standard deviation error bars are represented here). With maximum lumbar curvature, errors were negative and with minimum lumbar curvature, errors were positive. This indicates a small directional bias in the reposition errors towards a more neutral posture.

Results from Exp. 2. (A) Percent overestimation of finger lengths in “normal” and “rotated” postures. (B) Percent overestimation of knuckle spacings in the two postures. (C) GPS of actual hands (black dots/black lines) and body model in normal posture (white dots/dotted lines). (D) GPS of actual hands (black dots/black lines) and body model in rotated posture (gray dots/dashed lines). (E) Thin-plate spline depicting shape of body model in normal posture as a deformation of actual hand shape. (F) Comparable thin-plate spline for rotated posture.

Error (in degrees) in position sense tests was calculated as the absolute difference between the target lumbar curvature (not displayed) and the actual lumbar curvature. A, The error at a flexion angle of 0°; B, the error at a flexion angle of 30°; and C, the error at a flexion angle of 60°. This error increased significantly at flexion angles of 30° (B) and 60° (C). However, the error did not change with asymmetric (twist). In the fully flexed kyphotic posture, error was reduced.