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

Abstract

Free-operant and classical conditioning studies reporting additive summation, suppressive summation, and response averaging to compounded stimuli are reviewed, and a stimulus control model applicable to additive and suppressive summation in both paradigms is presented. A symmetrical composite-stimulus continuum, denned 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 ail-on and ail-off continuum extremes interchangeable. Moreover, additive summation, suppressive summation, and response averaging appear to be dependent on discrimination training, and determined by the history of, as well as the immediate relations between, response outputs and reinforcement densities conditioned to particular stimulus values along the composite training dimension. This evidence, and the stimulus control model derived therefrom, are used to functionally relate summation to generalization peak shift and to suggest 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.This review presents the current status of stimulus-compounding research in free-operant and classical conditioning, 3 and through this presentation it attempts to develop a comprehensive functional analysis of the variables involved in determining the various behavioral resultants reported within this experimental paradigm. The scope of the present paper does not extend to multiple-response or multiplechoice procedures, exemplified by the experiments of Schoeffler (1954) and Atkinson, Calfee, Sommer, Jeffrey, and Shoemaker (1964), but instead focuses on unitary response paradigms where variations in rates or magnitudes of response are of primary concern. Ultimately, the stimulus control analysis formulated is (a) discussed in terms of some

Learned together, extinguished apart: reducing fear to complex stimuli

“…Much of research on fear memories involves Pavlovian conditioning to a single, simple conditioned stimulus (CS); yet, in most fear disorders (e.g., PTSD), memories are complex-they integrate elements from a number of sensory modalities. Combination laws and compound learning theory suggest that individuals respond differently to a pair of compound-conditioned stimuli than they do to separately conditioned stimuli that are presented simultaneously at a later time (Rescorla and Wagner 1972;Weiss 1972;Kamin and Gaioni 1974;Mackintosh 1976;Kehoe and Gormezano 1980;Pearce and Hall 1980). At the neural level, both the hippocampus and the amygdala are required for the encoding and retrieval (ret) of complex fear memories, whereas discrete cued fear conditioning relies heavily on the lateral amygdala for these functions (Kim and Fanselow 1992;Phillips and LeDoux 1992).…”

Addition versus deletion as a signal

“…This criterion conforms to Weiss's (1972) definition of additive summation, in terms of greater response to a stimulus compound than to either individual component.…”

“…However, overall statistical support for the existence of additive summation was completely lacking in Experiment 4. Weiss (1972) has reviewed the literature on the topic, which includes a variety of settings where summation occurred in response to addition S+s.…”

“…Besides indicating whether the addition of the diffuse light was a more effective signal than its deletion-another test of the generality of our prior results-this new procedure allowed us to meaningfully compare responding to combinations of additions or deletions in final test sessions. Would the novel combination of two deletion S+ s yield more responses than either S+ alone, as has often been found for combinations of addition S+s (see Kehoe & Gormezano, 1980;Weiss, 1972)?…”

“…Besides providing more data on the effectiveness of additions as opposed to deletions as positive signals during training, these complex discriminations allowed us to test for possible summation of S+s, by means of a comparison of responding to combinations of S+ s with responding to the original training S+s themselves. Weiss (1972) has reviewed and contributed to the relatively small amount of research in which stimulus compounding of onsets is compared with that of offsets, and we hoped to look further at the issue of whether summation is equivalent for S+ combinations involving additions as opposed to deletions.…”