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Associability of a Previously Conditioned Stimulus as a Function of Qualitative Changes in the US

Hall and Pearce (1979) reported retarded manifestation of conditioned responding to repeated CS–strong shock pairings as a result of prior CS–weak shock pairings. These authors suggested that a latent inhibition (LI)-like process reduced the associability of the CS during weak shock conditioning despite excitatory associations between CS and weak shock being formed. The present experiments examined the possibility that the negative transfer from CS–weak shock conditioning in Stage 1 to CS–strong shock conditioning in Stage 2 observed by Hall and Pearce was due at least in part to the similarity between weak and strong shock rather than, or in addition to, a general loss of CS associability. Specifically, the transfer of decreased associability to conditioning with a dissimilar US was investigated. Consistent with Hall and Pearce, who gave multiple training trials in Stage 2, Experiment 1 found the development of conditioned responding owing to a single CS–strong shock pairing in Stage 2 to be retarded by prior CS–weak shock pairings and compared this effect to conventional LI. In Experiment 2, partial attenuation of the negative transfer following CS–weak shock was obtained by substituting ice water immersion for strong shock, that is, by making the strong US qualitatively dissimilar from the weak US. In contrast, conventional LI resulting from preconditioning CS-only exposures was equivalent for strong shock in Experiment 1 and ice water immersion in Experiment 2. A possible mechanism for the sensitivity to qualitative US changes of the observed negative transfer is discussed.