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The microstructure of licking responses was analyzed to investigate the interaction between unconditioned responses to maltodextrin and the responses to flavor cues previously associated with maltodextrin. Experiment 1 demonstrated that although the consumption of maltodextrin peaked at intermediate concentrations, the mean lick cluster size showed a positive, monotonic increase with concentration. In Experiment 2, a (conditioned stimulus) CS+ flavor was paired with 16% maltodextrin, whereas a CS- flavor was paired with 2% maltodextrin. During test, consumption of the CS+ was higher than that of the CS- when the flavors were combined with 2% maltodextrin, but not when combined with 16% maltodextrin. In contrast, cluster size was larger with the CS+ than with the CS-, regardless of the concentration of maltodextrin present on test. Previous analyses of licking microstructure indicate that cluster size reflects the palatability of the ingested solution. Thus, the present results indicate that flavor conditioning can change the palatability of the cue flavors. Adding the CS+ flavor to maltodextrin produced results analogous to increasing the concentration of maltodextrin (in terms of both consumption and licking microstructure measures), which is consistent with the idea that after conditioning, responses to the CS+ flavor and to the unconditioned stimulus are mediated via the same representation.
Humans and other omnivorous animals demonstrate unlearned positive reactions to only a very few tastes. The reaction to the sweet taste of sugars is perhaps the most well documented; however, there is also abundant evidence not only that rodents can detect the taste of polysaccarides, but also that they find their taste attractive (see Sclafani, 1987, and Sclafani, 2004, for reviews). In addition, it is well established that pairing an otherwise neutral flavor with a substance that elicits an unconditioned reaction will endow that cue flavor with the ability to elicit a reaction of its own (see, e.g., Capaldi, 1992; Rozin & Zellner, 1985; Sclafani, 1987). For example, rats will learn a preference for a flavor that is consumed along with glucose or fructose (e.g., Sclafani & Ackroff, 1994), or for a flavor that is paired with the gastric infusion of nutrients (e.g., Sclafani & Nissenbaum, 1988). Flavor preference learning of this type can be considered an example of Pavlovian conditioning: The flavor conditioned stimulus (CS) is paired with...