Do artificial limbs become part of the user? New evidence.

This paper provides evidence that limb-deficient subjects who wear artificial arms tend to overestimate the perceived length of their residual limb. It is proposed that this "perceptual error" may provide a useful and possibly more valid alternative to existing methods of determining prosthetic acceptance. The degree of overestimation is substantial for most subjects with amputations, and typically represents 20 percent of the length of the prosthetic arm. The effect is considerably reduced when the prosthetic limb is removed. Comparisons are made with normal-limbed subjects of various ages. For the most part, their errors are small and typically are underestimates of actual limb length. This research is compared with the work of Fraser (1984), who found similarities in reaching trajectories for normal and artificial arms. Further investigation is required to determine if this effect may serve as an index of adjustment to a prosthesis and, additionally, if prosthetics training programs might benefit from including techniques for enhancing perceptual adaptations to artificial limbs.