Enhanced preference for a flavour following reversed flavour—glucose pairing

In two experiments hungry rats showed enhanced preference for a flavour as a result of a procedure whereby the flavour followed presentation of 10% glucose—i.e. the reverse of the usual sequence. This provides the first example of excitatory conditioning resulting from reversed pairing involving an appetitive reinforcer. Experiment 1 compared a Cinnamon group, for which ingestion of glucose was followed after 3 min by cinnamon and on other days water was followed by wintergreen, with a Wintergreen group in which wintergreen followed glucose and cinnamon followed water. In a final 2-bottle test relative preference for cinnamon was greater in the Cinnamon than in the Wintergreen group. This effect was replicated in Experiment 2, which compared an Immediate group, for which, as above, drinking glucose was followed 3 min later by access to cinnamon, with a Delay group, for which there was a delay of 1 hr between glucose and subsequent access to cinnamon. Enhanced preference for cinnamon was found only in the Immediate group and appeared after only four glucose-cinnamon pairings. An important finding came from a choice test between glucose and saccharin in which the Immediate group showed a weaker preference for glucose than the Delay group. This indicated that a novel flavour may overshadow the association between the flavour of glucose and its consequences, which normally serves to enhance preference for glucose.