Figure 1.

Force-field learning and the perception of limb position. A, Subjects adapt to mechanical loads that displace the limb to the right or the left in proportion to hand velocity. Perceptual tests (gray) that estimate sensed limb position are interleaved with force-field training. Average movement curvature (±SE) is shown for null-field, force-field, and aftereffect phases of the experiment. B, The perceptual boundary between left and right is estimated using an iterative procedure known as PEST. The limb is displaced laterally by a computer-generated force channel, and subjects are required to indicate whether the limb has been deflected to the right. Examples are shown of individual PEST runs starting from left and right, respectively. The sequence beginning to the right is color coded to indicate the sequence of trials. C, A sequence of six PEST runs (starting from the top) with the lateral position of the hand shown on the horizontal axis and the PEST trial number on the vertical. The colored sequence of positions shown at the top is the same as that shown on the right side of B. PEST runs alternately start from the right and the left and result in similar estimates of the perceptual boundary. Note that the horizontal axis highlights lateral hand positions between 0 and 10 mm.