Contingency contrast effects in discrimination conditioning.

Three experiments observed differential electrodermal responding to signal stimuli (CSs) by contrasting positive, random, and negative contingencies between the signals and strong stimuli (UCSs). Experimentation began as a test of the proposition that electrodermal response to a random signal (or CSR) would lie between the response to a reinforced or excitatory stimulus (CS+) and that to a nonreinforced or inhibitory stimulus (CS- or CSI). A clear intermediate position for CSR did not result. Instead it appeared that CSR was operating as a mildly excitatory signal. This led to a second experiment where response to pairs of stimuli with different contingent relations could be compared in independent samples. The pairs were CS+ and CS-, CS+ and CSR, and CSR and CS-. Differential responding was observed in all pairs and response to CSR was significantly larger in the group receiving CSR with CS- than it was in the group receiving CSR with CS+. A contingency contrast effect was suggested. A third experiment explored the implications of a contingency contrast effect by varying overall UCS density, the duration of "safety intervals," and the presence or absence of instructions about contingencies. The UCS density and instruction variables influenced the differential performance to CSR and CS-, a result that was interpreted as further evidence for a perceptual contingency-contrast effect. Some theoretical implications of such a contrast phenomenon are examined, as they apply to autonomic learning. The CS is interpreted as a signal supplying contingency information that is dependent upon a complex of factors in the stimulation environment.