The Instrumentally-Derived Incentive-Motivational Function
- Author(s): Weiss, Stanley J.
- et al.
Though differential reinforcement, a discriminative stimulus (SD) acquires two properties. The operant contingency is responsible for the SDs response-discriminative property. However, as stimulus control develops an SD also acquires incentive-motivational properties through its association with reinforcement changes. A systematic series of experiments are described that breaks the usual co-variation of response and reinforcement rates in most discriminative operant situations. In three groups, SDs (a tone and a light) occasioned steady moderate lever pressing in rats that ceased when neither SD was present. Probably of reinforcement in these SDs, relative to when both were off, was systematically manipulated to make them incentive-motivationally excitatory, neutral or inhibitory. In each SD, for the “excitatory” group reinforcement (food) probability increased from 0 to 100%, for the “neutral” group it was unchanged and for the “inhibitory” group it decreased from 100 to 0%. Although behaviorally indistinguishable in training, a stimulus-compounding assay revealed that tone-plus-light tripled response rate in the incentive-excitatory group, doubled rate in the incentive-neutral group and didn’t increase rate in the incentive-inhibitory group – producing the instrumentally derived incentive-motivational function for the first time. This is discussed context of two-process learning theory, a functional analysis of transfer-of-control research plus how the response-discriminative and incentive-motivational properties acquired by an SD contribute to the stimulus control of behavior.