Three conditioned lick-suppression experiments with rats examined the
effects of pretraining exposure to the conditioned stimulus (CS) on be
havior indicative of conditioned inhibition. After CS-preexposure trea
tment, subjects received either Pavlovian conditioned inhibition train
ing or explicitly unpaired inhibition training with the preexposed CS.
The inhibitory status of the CS was then assessed with a retardation
(Experiment 1) or a summation (Experiment 2) test. Experiment 3 contro
lled for the unconditioned stimulus-preexposure effect being a potenti
al confound in Experiments 1 and 2: As predicted by the comparator hyp
othesis (R. R. Miller gr L. D. Matzel, 1988), the CS-context associati
on that developed during the CS-preexposure phase disrupted the expres
sion of Pavlovian conditioned inhibition but not the expression of exp
licitly unpaired inhibition.