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^Ds. 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^Δ condition was tone-and-light absence ($\bar{T}$+$\bar{L}$). Tone-plus-light (T+L) was S^Δ 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 $\bar{T}$+$\bar{L}$ as S^Δ and $\bar{T}$+$\bar{L}$ for the group trained with T+L as S^Δ. The S^Δ 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 $\bar{T}$+$\bar{L}$. 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.