In Experiment 1 rats were given training in which a mixture of two flavors was paired with sucrose. This
established a substantial preference for each of the flavors; however, when rats were given prior expe-
rience with just one of the flavors paired with sucrose, training with the compound produced only a weak
preference for the other – an example of the blocking effect, well known in other associative learning
paradigms. Both the palatable taste of sucrose and its nutrient properties contribute to its ability to re-
inforce preference acquisition. The role of these two forms of learning was examined in two further ex-
periments in which the reinforcer used was fructose (which is considered to support preference learning
because it is palatable but not through its nutrient properties) or maltodextrin (thought to support pref-
erence learning by way of its nutrient properties). In neither case was blocking observed. At the theo-
retical level, this outcome constitutes a challenge to the attempt to explain flavor-preference learning in
terms of the standard principles of associative learning theory. Its implication at the level of application
is that the potential of the blocking procedure as a technique for preventing the development of un-
wanted flavor preferences may be limited.