Nine Sprague-Dawley male albino rats were randomly assigned to each of 5 groups. Three groups received differential conditioning to small (S) and large (L) reward. One group (LS) experienced L-S transitions, a 2nd group (SL) experienced S-L transitions, and a 3rd group (LS-SL) received the combined sequences of Groups LS and SL. Two control groups received only L or S trials. Negative contrast (slower speeds in the S-alley than the S control group had) was demonstrated for all 3 differential groups, and positive contrast (faster speeds in the L-alley than the L control group had) was demonstrated in Groups LS and SL, but not LS-SL. In extinction, Groups S and L showed the usual between-S differences in resistance to extinction (S more resistant than L); Groups LS and LS-SL also showed this effect, based on the within-S procedure. Group SL showed the opposite effect, which was predicted by an extension of the sequential hypothesis of extinction effects. (22 ref) (PsycINFO Database Record (c) 2006 APA, all rights reserved)