A clarification of the nature of backward excitatory conditioning

This study further tested a behavior systems view of backward excitatory conditioning. In the first phase, two groups of rats were exposed to an 8-s light CS that either followed (Group Backward) or preceded (Group Forward) the delivery of food. In the second phase, a novel lever was compounded with the last half of the 8-s CS, and the offset of this compound stimulus was followed by food. A third group of rats (Group Control) was exposed to the compound conditioning phase without prior training. Lever contact was highest when the lever was compounded with the previously backward CS. Groups Forward and Control did not differ significantly in lever contact. The results supported the hypothesis that a proximate backward CS acquires control of a postfood focal search mode. In addition, the results argued against blocking as necessary to produce a difference between Groups Backward and Forward in responding to a compound forward stimulus. (C) 2000 Academic Press.