Conditioned preferences for the taste and odor components of flavors: blocking but not overshadowing

Sprague-Dawley rats were given two water bottles. One bottle contained sucrose and the other did not. Distinctive odors and/or tastes were paired with sucrose or plain water solutions. Preferences for the odor and taste were then measured under iso-caloric conditions when the rats were and were not food deprived. The rats preferred the odor or taste that had previously been paired with sucrose. The strength of this preference increased when the rats were food deprived suggesting that the effect was calorie mediated. The development of a preference to the odor or taste was not affected by the addition of a taste or odor; there was no evidence of overshadowing. Conditioned taste and odor preferences were partially blocked by prior pairing of the odor or taste with sucrose. The absence of overshadowing, but not the presence of blocking, was predicted by a theory of associative learning which treats odors as conditioned stimuli, tastes as unconditioned stimuli and ingestional consequences (e.g. calories or illness) as a new category referred to as feedback.