The effect of two ways of devaluing the unconditioned stimulus after first- and second-order appetitive conditioning.

Rats received first- and second-order conditioning based upon a food unconditioned stimulus (UCS). They then received one of two manipulations designed to reduce the value of that food, satiation, or pairing of food with high-speed rotation. The effects of these manipulations were assessed during extinction tests of the conditioned stimuli (CSs). Compared with controls, both manipulations reduced the activity produced by the first-order CS but did not affect that produced by a second-order CS. The results are interpreted as consistent with those from aversive UCSs in implying the involvement of a UCS representation in first- but not in second-order conditioning. They also suggest that a major effect of satiation is to reduce the value of the UCS.