On the basis of computational studies it has been proposed that the central nervous system (CNS) internally simulates the dynamic behavior of the motor system in planning, control, and learning; the existence and use of an such an internal model is still under debate. A sensorimotor integration task was investigated in which subjects estimated the location of their hand at the end of movements made in the dark, and under externally-imposed forces. The temporal propagation of errors in this task was analyzed within the theoretical framework of optimal state estimation. Our results provide direct support for the existence of an internal model.
In Science (1995) 269: 1880-1882, postscript.