Does drinking saccharin weaken an association of sweet with calories? Pre-exposure effects in flavor preference learning.

The main aim of this experiment was to examine the claim that exposure to non-nutritive sweeteners weakens the formation of a sweet-calorie association. Three groups of food-deprived rats received training in which they drank an almond-flavored maltodextrin and saccharin solution. A final test phase assessed their preference for almond. The groups differed in preexposure prior to training. One was pre-exposed to saccharin, one to saccharin plus maltodextrin, and the third, control condition, received only water at this stage. When the rats continued under food deprivation for the test phase, the group exposed to the compound (saccharin plus maltodextrin) showed a weaker preference than the other two groups, while those pre-exposed to saccharin showed as strong a preference as the controls. When the test was conducted with the rats no longer food-deprived, only the water group showed a strong preference. These results support the proposal that rats can form both flavor-flavor and flavor-nutrient associations, expression of which will depend on motivational state. They did not find support for the suggestion that prior exposure to a non-nutritive sweetener can enhance subsequent learning about the nutritive properties of a sweet food.

Tests for inhibition after extinction of a conditioned stimulus in the flavour aversion procedure.

In four experiments, rats received flavour aversion conditioning followed by extinction. The flavour was then subjected to retardation and summation tests. Experiment 1 showed that reacquisition of an extinguished flavour aversion was retarded with respect to the performance shown by rats for whom the flavour was novel. No retardation was found, however, with respect to a control group that had been given non-reinforced pre-exposure to the flavour. Experiment 2 demonstrated that extinction showed the same sensitivity to the effects of a retention interval as did latent inhibition, consistent with the view that the retardation effect was a consequence of the occurrence of latent inhibition during extinction. An extinguished stimulus was also found to alleviate the response governed by a separately trained excitor in a summation test (Experiments 3 and 4), but the size of this effect did not exceed that produced by a control stimulus when the procedure used ensured an equivalent aversion to the test excitor in the two cases. These results challenge the proposal that extinction can turn a stimulus into a net inhibitor.

Role of stimulus ambiguity in conditional learning.

Three experiments using rats and the conditioned emotional response procedure examined the notion that when a conditioned stimulus (CS) is paired with a reinforcer (US), that CS must be ambiguous if the CS-US association is to become the target of conditional control. CS ambiguity was manipulated by varying whether the CS had been preexposed prior to conditioning. In Experiments 1 and 2, it was demonstrated that a cue that accompanied pairings of a CS and shock acquired conditional control over the CS-shock association when that CS had been preexposed, but not when it was novel. The measure of conditional control in Experiments 1 and 2 was the ability of the (conditional) cue to enhance responding to the target CS. Experiment 3 used a blocking procedure to show that this enhancement reflected an amplification of the target CS's effective associative strength. These findings extend existing knowledge of the conditions required for conditional cue formation.