Abstract
The study of artificial arms provides a unique opportunity to address long-standing questions on visuomotor plasticity and development. Learning to use an artificial arm requires an interplay between vision, sensation, and movement to form the fundamental building blocks of body representation across early life experience. To uncover these processes, we tested how early experience with an artificial or biological arm shapes visually guided reaching behaviour. We did this by testing artificial arm motor-control with and without visual feedback in two adult populations with upper-limb deficiencies: a congenital group – individuals who were born with a partial arm, and an acquired group – who lost their arm following amputation in adulthood. Brain plasticity research teaches us that the earlier we train to acquire new skills (or use a new technology) the better we benefit from this practice as adults. Instead, we found that although the congenital group started using an artificial arm as toddlers, they produced increased error noise and directional errors when reaching with visual feedback, relative to the acquired group who performed similarly to controls. However, the earlier an individual with a congenital limb-difference was fitted with an artificial arm, the better their motor control was. We found no group differences between the amputee and congenital group when reaching without visual feedback. We also found that the group differences in visually guided reaching could not be explained by present artificial-arm use, passive proprioception, or speed-accuracy trade-offs. This suggests that the ability to perform efficient visual-based corrective movements is highly dependent on either biological or artificial arm experience at a very young age, but subsequently, opportunities for visuomotor plasticity become more limited.