Mediated inhibition and excitation of flavor cues in sensory preconditioning
Privitera, Gregory Joseph
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When a subject is exposed to a compound stimulus, AB, then subsequently becomes ill following consumption of B (i.e., the trained flavor), the subject will form an aversion to the stimulus previously associated with B (the subject will reduce consumption of the test flavor A). This phenomenon has been termed sensory preconditioning (SPC) and is denoted as the AB/B+ paradigm, with + denoting reinforcement (Brogden, 1939). Using this sensory preconditioning paradigm, the appropriateness of the testing methods for 2 commonly employed designs while varying the unconditioned stimulus (US) strength (i.e., .1 M versus .3M lithium chloride [LiCl]) was examined. Using a between-subject comparison design, Experiments 1A and 1B employed 2- and 1-bottle tests, respectively. Using a within-subject comparison, Experiment 1C employed 2-bottle tests. The results showed that an aversion to flavor A was not expressed with a weaker US (i.e., .1 M LiCl), although this US did produce a significant aversion to flavor B. Experiment 2 showed that following 2 days of testing, flavor A may have inhibitory and excitatory properties for subjects trained with the weaker US. Experiments 3 (retardation test) and 4 (summation test) both showed evidence for conditioned inhibition following 4 days of SPC testing for subjects trained with the weaker US, but not the stronger US. Experiments 5 and 6 showed that weakening the salience of the extract (either by decreasing its concentration or presenting them on disks) reinstated effective sensory preconditioning to the extracts for subjects receiving a relatively weaker US in training. The results suggest that flavor A acquired excitatory properties in training via its representation, and also acquired inhibitory properties during testing, the rate of which was at least partially dependent upon the salience of A, B, and the intensity of the US. This form of learning is presently termed mediated conditioned inhibition , since inhibition to A was mediated by the representation of the now excitatory B in test. Furthermore, these results are best explained by elemental theories of conditioning and, as such, are applied to the Rescorla-Wagner model.