Injected 17 18-24 yr. old males with bipolar fine-wire electrodes into the tibialis anterior muscle. A start light indicated the onset of a trial. If Ss activated a single motor unit, a correct light appeared. With no additional feedback, Ss learned to isolate and control a single motor unit within 500 trials and demonstrated significant improvement during a relearning series. (PsycINFO Database Record (c) 2006 APA, all rights reserved)