Stimulus compounding in free-operant and classical conditioning: A review and analysis.

Reviews previous free-operant and classical conditioning studies reporting additive summation, suppressive summation, and response averaging to compounded stimuli. A stimulus control model applicable to additive and suppressive summation in both paradigms is presented. A symmetrical composite-stimulus continuum, defined by the on-off states of the discriminative or conditioned stimuli controlling behavior in training, is seen to be common to both types of summation, with the functions of the all-on and all-off continuum extremes interchangeable. Moreover, additive summation, suppressive summation, and response averaging appear to be (a) dependent on discrimination training; and (b) determined by the history of, and immediate relations between, response outputs and reinforcement densities conditioned to particular stimulus values along the composite training dimension. This evidence and the derived stimulus control model are used to functionally relate summation to generalization peak shift. It is suggested that these additive, suppressive, and averaging effects to compounded stimuli might further help in clarifying, and in placing in contextual perspective, what are currently thought of as "excitatory" and "inhibitory" mechanisms in learning. (72 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)