Can rats learn to associate a flavour with the delayed delivery of food?

Associations between a specific flavour and access to food were studied using a discrimination procedure devised by Holman (1975). This involved giving rats one flavour (e.g. cinnamon) of saccharin solution on some days, and following this by delivery of food, and a second flavour (e.g. wintergreen) on other days which was never followed by food. Experiment 1 used glucose delivered after a 30-min delay and a slight increase in preference for the paired flavour was detected. Using a 20-min delay Experiment 2 varied the kind of food used; some evidence for discrimination learning was again found in the glucose group, but there was no evidence that rats could associate a flavour with starch solution or solid chow over this delay. To check that the general procedure was a sensitive one, in Experiment 3 one flavour was added to glucose i.e. without delay, and this produced large shifts in a subsequent preference test. Overall the results threw doubt on claims that rats as readily form flavour-calorie associations over delays as they do flavour-toxicosis associations.