Withdrawal of reinforcement usually refers to the withdrawal of a stimulus which is the occasion on which a performance may be reinforced. Withdrawal of reinforcement is to be distinguished from extinction, which designates the emission of the performance without reinforcement. In withdrawal of reinforcement the stimulus already controls a zero or near zero rate of a performance. Thus, the result of withdrawing a stimulus that controls positive reinforcement is to reduce the frequency of reinforcement without extinction. The stimulus which controls a zero rate of performing also has the properties of an aversive stimulus, and may function similarly to an electric shock in punishment, avoidance, escape, or a preaversive stimulus.