Abstract
Two severely retarded boys, each a member of a different play group, experienced three regimes of reinforcement from adults [contingent, noncontingent, and mixed (contingent and noncontingent)]. The agent of contingent reinforcement acquired stimulus control of the subjects' behavior; the noncontingent agent did not. The agent of the mixed schedule of reinforcement did not gain control, but aspects of his behavior came to function as cues. The mixed adult's withholding reinforcement in the absence of the target behavior (cooperative play) evoked cooperative play, whereas his presenting free reinforcement resulted in the subjects' remaining in their inactive, baseline positions.