A further application of composite-stimulus control in additive summation

Discriminated response and incentive processes in operant conditioning: a two-factor model of stimulus control

Understanding stimulus control generated in instrumental learning requires the direct investigation of discriminated response and reinforcer (incentive) processes acquired exclusively through the response-reinforcer contingencies operating on complex (multicomponent) baselines. Two series of stimulus-compounding studies accomplished this direct investigation. In one series, the independent variable was the relative reinforcement between schedule components; in the second series, it was relative response rate between components. Stimulus-compounding tests revealed that response and incentive processes enhanced each other when in agreement, counteracted each other when in opposition, and produced intermediate results when only one factor was operating. This pattern of results led to the conclusion that these factors were algebraically combining and to the development of a response/incentive matrix reflecting these dynamics. This two-factor analysis was extended to the peak-shift effect in stimulus generalization experiments and to the generation of inhibitory control. Two decades of stimulus compounding and peak-shift research were organized within this two-factor framework, extending this traditional approach to learning to active research areas heretofore not systematically considered in these terms.

Within-subject reversibility of discriminative function in the composite-stimulus control of behavior

According to the composite-stimulus control model (Weiss, 1969, 1972b), an individual discriminative stimulus (S(D)) is composed of that S(D)'s on-state plus the off-states of all other relevant S(D)s. The present experiment investigated the reversibility of composite-stimulus control. Separate groups of rats were trained to lever-press for food whenever a tone or a light S(D) was present. For one group, the nonreinforced S(Delta) condition was tone-and-light absence (T+L). Tone-plus-light (T+L) was S(Delta) in the other group. On a "stimulus compounding" test that recombined composite elements, maximum responding occurred to that composite consisting only of elements occasioning response increase. That was T+L for the group trained with T+L as S(Delta) and T+L for the group trained with T+L as S(Delta). The S(Delta) composite was next reversed over groups in Phase 2. In Phase 2 tests, maximum responding that was comparable in magnitude to that of Phase 1 was again controlled by the composite consisting only of elements most recently occasioning response increase-whether T+L or T+L. The inhibitory conditioning history of both composite-elements currently occasioning responding did not weaken the summative effect. These results confirm and extend Weiss's composite-stimulus control model, and demonstrate that such control is fully reversible. We discuss how translating conditions of the stimulus-compounding paradigm to a composite continuum creates a functional and logical connection to intradimensional control measured through stimulus generalization, reducing the number of different behavioral phenomena requiring unique explanations.

Stimulus control of cocaine self-administration

Environmental stimuli that set the occasion wherein drugs are acquired can "trigger" drug-related behavior. Investigating the stimulus control of drug self-administration in laboratory animals should help us better understand this aspect of human drug abuse. Stimulus control of cocaine self-administration was generated here for the first time using multiple and chained schedules with short, frequently-alternating components--like those typically used to study food-maintained responding. The procedures and results are presented along with case histories to illustrate the strategies used to produce this stimulus control. All these multicomponent schedules contained variable-interval (VI) components as well as differential-reinforcement-of-other-behavior (DRO) or extinction components. Schedule parameters and unit dose were adjusted for each rat to produce stable, moderate rates in VI components, with minimal postreinforcement (infusion) pausing, and response cessation in extinction and DRO components. Whole-body drug levels on terminal baselines calculated retrospectively revealed that all rats maintained fairly stable drug levels (mean, 2.3 to 3.4 mg/kg) and molar rates of intake (approximately 6.0 mg/kg/hr). Within this range, no relation between local VI response rates and drug level was found. The stimulus control revealed in cumulative records was indistinguishable from that achieved with food under these schedules, suggesting that common mechanisms may underlie the control of cocaine- and food-maintained behavior.