Variable processing of flavours in rat STM
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The research reported in this thesis examines factors that affect the willingness of rats to ingest novel flavour solutions. Emphasis is placed on the memorial processes assumed to underlie the decision as to whether or not a solution is "safe" to drink. Rats exhibit caution (neophobia) in consuming an unfamiliar (target) solution. This unconditional response to novelty habituates as the rat acquires experience with the target solution (provided that ingestion of the target solution has no noxious consequences!). Neophobia to the target solution may be restored, however, if another (distractor) solution is presented during the interval separating pre-exposure to, and testing of, the target solution (Green & Parker, 1975). In Section 1, the phenomena of habituation to an iterated target stimulus and the disruption of this process by a distractor are introduced. Theoretical explanations of the "dishabituation" effect of a distractor stimulus are described and assessed. The possibility of an empirical test of the relative validity of the Robertson and the Wagner hypotheses using the attenuation of flavour neophobia procedure of Green and Parker provided the impetus for the experiments reported in Section 2. In Section 3, attention is drawn to the similarity of the procedure designed to establish habituation and that Intended to establish latent inhibition to a stimulus. A limited review of empirical data is presented testifying to the fact that habituation and latent inhibition are affected similarly by identical parameter manipulations. The Wagner (1976) model views habituation and latent inhibition as the outcome of a common underlying process, Expts. 10a and 10b, therefore, sought to determine whether latent inhibition of a conditioned taste aversion (CTA) to lemon or sucrose solution would be affected by a coffee distractor in a manner consonant with predictions derived from the results of the neophobia experiments reported in Section 2. The distractor, however, had no effect on strength of latent inhibition in either experiment. Expt. 11c demonstrated that it is possible for a distractor (30% vanilla) to disrupt attenuation of neophobia to a target flavour (3% cider vinegar) without affecting latent inhibition to the target flavour, i.e., there is no direct correspondence between measures of habituation and latent inhibition to the same stimulus. In Section 4, the phenomena of overshadowing and potentiation of a CTA are introduced. At least one explanation of potentiation (c.f., Durlach & Rescorla, 1980) stresses the importance of an association between the elements of a compound CS. Rescorla and Furrow (1977) found interstimulus associations were formed more rapidly between similar rather than dissimilar stimuli. Given these results, Expts. 12a and 12b sought to determine whether a single sequential presentation of lemon and coffee (similar solutions) paired with LiCl would result in potentiation of a conditioned aversion to the lemon solution and whether a single sequential presentation of sucrose and coffee (dissimilar solutions) paired with LiCl would result in overshadowing of a conditioned aversion to the sucrose solution. These experimental predictions were confirmed. In Section 5, a potential confound in the neophobia experiments is addressed. Interpretation of attenuated neophobia as a habituation process is defended and alternatives to the Wagner (1976) theory of habituation are considered for their ability to encompass the data reported in Section 2. Only the Wagner model, however, appears able to account for all the data. Nevertheless, some limitations of the model are indicated. Finally, the conditions promoting overshadowing and potentiation of a CTA are discussed. (Abstract shortened by ProQuest.)
Thesis, PhD Doctor of Philosophy
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