Abstract
In the classical conditioning, the temporal relationship between a conditioned stimulus (CS) and an unconditioned stimulus (US) has an effect on the strength of elicited conditioned responding (CR). The present study explored the effect of temporal relationship between a first-order CS (CS1) and an US on CR to the CS1 and a second-order CS (CS2) in rats' conditioned licking suppression. Strong CR was elicited by the CS1 in groups where the CS1 was presented before the US, weak CR in a group where the CS1 and the US were presented simultaneously, and little CR in groups where the CS1 was presented after the US. The amount of CR to the CS2 was monotonously corresponded to the amount of CS1-elicited CR. These results were different from those of recent studies.
