Duration of plastic change in a modifiable efference copy.

A modifiable efference copy associated with the motor command that elicits an electric organ discharge (EOD) is found in mormyrid electric fish. It is a negative image of the expected effect of the afferent input that follows the EOD. A change in the afferent input pattern causes, over time, a corresponding change in the efference copy. The negative image is retained for at least one half-hour when the motor command is artificially silenced.