Differential effects of expectancy and associative mechanisms on diminution of unconditioned response in electrodermal classical conditioning

blink reactions, reduced response to the unconditioned stimulus (US) after repeated pairing of a conditioned stimulus (CS) with the US has been frequently observed (Baxter, 1966; Kimmel, 1967; Kimmel & Pennypacker as described in Kimmel, 1966). This phenomenon has been called «conditioned diminution of the unconditioned response (UR)» (Kimble & Ost, 1961), and a range of explanations have been offered. An important issue is whether the conditioned diminution of the UR has an associative basis (Kimble & Ost, 1961). Much research on human subjects in electrodermal conditioning has supported the interpretation that diminished UR, seen in the presence versus the absence of a training CS, depends upon the associative integrity of the CS (Donegan & Wagner, 1987, p. 340). Experiments carried out by Baxter (1966), Kimmel (1967) and Kimmel and Pennypacker (described in Kimmel, 1966) seem to confirm a deteriorative effect of conditioning on the amplitude of the UR. However, other parallel research has not been able to reproduce these findings (Grings & Schell, 1969, 1971). Morrow (1966) conducted a particularly convincing test of the associative basis of the conditioned diminution. If the conditioned diminution of the UR depends on the association CSUS, then it should be attenuated by extinguishing the conditioned response (CR). Using this procedure, Morrow found that extinguishing the CR led to a recovery of US effectiveness on postextinction CS-US test trials. However, these results should be considered as tentative since the extent of the recovery was the same for groups receiving different numbers of extinction trials. More recently, Donegan and Wagner (1987, Experiment 2), working on the rabbit conditioned eyeblink preparation, demonstrated the presence of discriminative control over the conDifferential effects of expectancy and associative mechanisms on diminution of unconditioned response in electrodermal classical conditioning