Detection of adaptive inverse models in the human motor system

This study aimed to find evidence for the formation of an internal inverse model of a novel visuomotor relationship for feedforward control in the bra in. An experiment was carried out involving 20 normal adult subjects who pe rformed a pursuit random tracking task with a steering wheel for input. Dur ing learning the response cursor was periodically blanked, removing all fee dback about the external system (i.e., about the relationship between hand motion and response cursor motion). Results showed a transfer of learning f rom the unblanked runs to the blanked runs for a static nonlinear system (l inear trend RMS error F(1, 19) = 5.05, p = 0.037) thereby demonstrating ada ptive feedforward control in the nervous system. No such transfer was obser ved for a dynamic linear system, indicating a dominant adaptive feedback co ntrol component. Results are consistent with inverse modeling and suggest a combination of feedforward and feedback adaptive control in the brain. (C) 2000 Elsevier Science B.V. All rights reserved.