Weight-lifting by normal and deafferented monkeys: evidence for compensatory changes in ongoing movements.

When trained in a weight-lifting paradigm, both normal and deafferented monkeys achieved high reinforcement densities at all test weights employed. Recordings of acceleration on the first lift of an unknown weight reveal that at some delay after the start of movement deafferented monkeys can alter the subsequent trajectory by a sudden change in applied torque. Comparison with normal animals indicates that short latency feedback pathways in normal animals contribute to the smoothness of movements made in the face of unknown external loads.