Fig. 2: Position Pointing Task.

a The participant’s reference arm was strapped to a paddle, hidden behind a screen. With their other arm they moved the pointer paddle, rotating it by means of a lever at its base. Both paddles had potentiometers at their hinge joints to provide a continuous output of elbow angle. The task was to move the pointer paddle to a position where it was perceived to be in line with the hidden reference forearm. b Plot of the angle indicated by the pointer paddle against the position of the hidden reference forearm. Position errors measured at each of a range of test angles between 90° (forearm vertical to supporting base) and 0° (forearm fully extended). Dashed line, reference and indicated positions are identical. Values above the line, errors into extension. At each test angle, the reference arm was subjected to three different thixotropic conditionings, shown in red, green or blue. For each colour the plotted value represents the mean ( ± SD) of three repeated measurements at that angle, pooled for 10 participants. The shaded portion of the angle range indicates where position errors became progressively smaller. Figure modified and redrawn from Chen et al. ²⁴.