Super-latent inhibition of conditioned taste preference with a long retention interval

Effects of food deprivation on conditioned orthonasal olfactory preferences with caloric and non-caloric reinforcers

Three experiments were conducted to investigate Conditioned Olfactory Preferences using orthonasal inhalation, which is a less explored perceptual pathway compared to retronasal inhalation. In these experiments, odors were impregnated onto plastic disks to prevent the subjects from consuming or tasting them. The reinforcers used were a sucrose solution (Caloric groups) and a saccharin solution (Non-Caloric groups). The influence of nutritional deprivation was analyzed, with unrestricted access to food throughout the procedure in Experiment 1, food restriction during the conditioning phase in Experiment 2, and limited access to food during the test phase in Experiment 3. The results revealed conditioned preferences using both sucrose and saccharin as reinforcers. Furthermore, dietary restriction reduced the conditioned preference induced by saccharin, but not the preference induced by sucrose. These findings are discussed in light of the potential differences between orthonasal and retronasal presentation of odors during conditioning.

Facilitation and retardation of flavor preference conditioning following prior exposure to the flavor conditioned stimulus

In two experiments, rats received pairings of an almond flavor (Experiments 1 and 2B) or a vanilla flavor (Experiment 2A) with sucrose. In each experiment, half of the rats received prior exposure to the flavor and half were exposed to water. Conditioned preference was then assessed through two-bottle, flavor versus water, choice tests. Latent inhibition (indicated by a weaker preference in pre-exposed subjects) was observed in the experiment using the vanilla flavor. However, facilitation (a stronger preference in pre-exposed subjects) instead of latent inhibition was evident with the almond flavor, both across acquisition trials and in the final choice test. These results indicate that, unlike most other paradigms of Pavlovian conditioning, conditioned stimulus pre-exposure in flavor preference learning may either facilitate or retard the acquisition (or the expression) of a conditioned flavor preference. We explore the proposal that the critical difference between the flavors lies in their hedonic values, with facilitation being more likely in a flavor that is initially disliked.

Latent inhibition in flavor-preference conditioning: effects of motivational state and the nature of the reinforcer

In two experiments, rats received pairings of the flavor of almond with either fructose or maltodextrin, and the conditioned preference for almond was then tested. In each experiment, half of the rats had received prior exposure to almond on its own, and half had received no preexposure. In Experiment 1, in which the rats were hungry during the test, the preference was greater in the nonpreexposed subjects, both for those trained with fructose and those trained with maltodextrin; that is, latent inhibition was obtained with both reinforcers. In Experiment 2, in which the rats were not food deprived prior to the test, not only was there no latent inhibition with either of the reinforcers, but, for both, the preference was greater for preexposed than for nonpreexposed subjects. These results give no support to the proposal that different types of reinforcer generate different types of learning. They are, however, consistent with the proposal that different types of learning control behavior when a rat is hungry and when it is not, and that the form that generates the preference in the latter case is not susceptible to the latent inhibition effect.

Analysis of blocking of flavor-preference conditioning based on nutrients and palatable tastes in rats

In Experiment 1 rats were given training in which a mixture of two flavors was paired with sucrose. This established a substantial preference for each of the flavors; however, when rats were given prior experience with just one of the flavors paired with sucrose, training with the compound produced only a weak preference for the other - an example of the blocking effect, well known in other associative learning paradigms. Both the palatable taste of sucrose and its nutrient properties contribute to its ability to reinforce preference acquisition. The role of these two forms of learning was examined in two further experiments in which the reinforcer used was fructose (which is considered to support preference learning because it is palatable but not through its nutrient properties) or maltodextrin (thought to support preference learning by way of its nutrient properties). In neither case was blocking observed. At the theoretical level, this outcome constitutes a challenge to the attempt to explain flavor-preference learning in terms of the standard principles of associative learning theory. Its implication at the level of application is that the potential of the blocking procedure as a technique for preventing the development of unwanted flavor preferences may be limited.

Motivational control of latent inhibition in flavor preference conditioning

In three experiments, rats given pairings of a neutral flavor with sucrose showed a preference for that flavor when subsequently allowed to choose between it and water. Preexposure to the flavor produced a latent inhibition effect (reduced the size of the preference) when the rats were hungry during the test (Experiments 1 and 2). Rats that were not hungry during the test failed to show latent inhibition (Experiments 1-3). Experiment 3 confirmed that sucrose-flavor pairings were capable of producing a preference even in nonhungry rats. It is argued that the preference shown by rats that are hungry on test depends on a flavor-nutrient association, a form of learning that is susceptible to latent inhibition in the same way as standard conditioning procedures are. The failure to obtain latent inhibition in nonhungry rats suggests that the preference obtained in these conditions depends on a different form of learning that is less susceptible to the effects of stimulus exposure.

Effects of context novelty vs. familiarity on latent inhibition with a conditioned taste aversion procedure

The latent inhibition phenomenon is observed when a conditioned stimulus is preexposed without any consequence before conditioning. The result of this manipulation is a reduction in conditioned response intensity to such a stimulus. In this study, we analyse the role of context novelty/familiarity on LI modulation by changing the context using a three-stage conditioned taste aversion procedure. Experiment 1 revealed that, similar to other learning procedures, a context change between preexposure and conditioning/testing (but not between preexposure/conditioning and testing) resulted in LI attenuation when the experimental contexts were novel. Experiment 2, using animals' home cages as one of the contexts, revealed a different pattern of results, with an unexpected increase in LI magnitude when the context change was introduced between conditioning and test stages. The Schmajuk et al. (1996) computational model explains these results in terms of the increased novelty of the conditioned stimulus during preexposure, conditioning, and testing.