Early experience and reinforcer quality in delayed flavour-food learning in the rat.

The ability of hungry rats to associate flavours with the consequences of ingesting glucose solutions was studied in three experiments. Experiment 1 used a procedure in which on some days one flavour, e.g. cinnamon, was presented and followed after 20 min by 20% glucose, while on other days a second flavour, e.g. wintergreen, was presented, but not followed by any event. During this training, subjects who received quinine-tainted glucose increased their consumption of the predictive flavour relative to groups given no quinine, but quinine tainting did not affect conditioned preference for the predictive flavour in choice tests. With the aim of discovering whether prior experience of a variety of foods improves ability to learn new flavour-calorie associations, Experiment 2 and used a similar procedure to compare subjects raised on a varied diet ("supermarket" rats) with controls previously given only chow. Contrary to expectation, the supermarket rats showed some impairment both on this delay task and, in Experiment 3, on one using a "mixtures" procedure. This involved presenting a mixture of one cue flavour with glucose-quinine on some days and a mixture of a second cue with an equally palatable saccharin solution on other days. Acquisition was particularly rapid in control subjects, reaching asymptote after only two flavour-glucose pairings. It was concluded that neither a decrease in palatability, as in Experiment 1, nor prior experience with a range of foods, as in Experiments 2 and 3, improve a rat's ability to associate a new flavour with calories.