Inaccurate Grip Predictions for Congenital Amputees’ Absent Hand: Evidence of Sensory-dependent Construction of Accurate Internal Models for Motor Planning

To what extent does accurate internal model construction, for motor planning, depend on sensory experience? A previous study showed preserved accuracy of models for traumatic amputees’ absent hand (Philip & Frey, 2011). We investigated whether accurate internal models depend on initial limb presence. Five congenital upper limb amputees and matched controls performed two grip selection tasks: overt grip selection (OGS), where participants explicitly grasped a presented stimulus with their intact hand; and prospective grip selection (PGS), where judgments were made for either hand while remaining stationary. Predictive accuracy was calculated by comparing PGS directly to OGS for intact hand, and to the inversed OGS for absent hand. Amputees did not signifi- cantly differ in overall accuracy from controls [F(1,4)=4.49, p=0.10], or between hands [F(1,4)=0.13, p=0.74]. However, a significant accuracy-orientation pattern for amputees’ absent hand, [F(1,4)=7.908, p=0.048] was found. This suggests amputee’s directly use their intact hand for decisions about absent hand, supporting sensory-dependent construction of internal hand models for motor planning.