Figure 2. Position-matching errors in the vertical plane.

Values are means (±s.e.m.) for 12 subjects. Matching errors in the direction of extension are shown as positive. Dotted line, zero error. For this experiment both arms had been flexion conditioned before each matching trial. The four conditions for the reference arm were: supported by the experimenter, supported by the subject, supported by the subject with a 10% maximum voluntary contraction load added, and supported by the subject with a 25% load added. Despite one arm bearing an increasingly heavy load, matching accuracy remains unaffected. From Allen et al. (2007).