Posted by: Indonesian Children | November 26, 2009

Olfactory and Gustatory Stimuli in Food-Aversion Learning of Rats

Journal article by Klaus Schneider, Marlies Pinnow; Journal of General Psychology, Vol. 121, 1994

Journal Article Excerpt

Olfactory and Gustatory Stimuli in
Food-Aversion Learning of Rats

Faculty of Psychology
Bochum, Germany

ABSTRACT. Two studies of food-aversion learning in the rat examined some crucial conditions for the potentiation of an odor component by a novel taste. Wistar rats were exposed twice to an odor-taste compound and then were treated either immediately or the next day with lithium chloride, a noxious substance. Immediately poisoned rats acquired an aversion to the odor component when it was paired with a familiar taste. Only in one experimental condition did some weak conditioning occur: when the now odor was presented together with a new taste. Thus, the classical phenomenon of overshadowing of the less salient odor component by the more salient taste was observed in all of our studies. This was true for situations in which the odor was presented near the drinking spout as well as for situations in which the odor was presented at some distance in front of the drinking source (Experiment 1). In addition, the weaker an odor component was, the more easily it was overshadowed by the taste (Experiment 2). All results fit well into classical rules of Pavlovian conditioning and fail to support the assumption that special mechanisms exist in food-related odor conditioning in rats.

IN PAVLOVIAN CONDITIONING, when two conditioned stimuli (CS) are pre-
sented together in a compound, the less potent and/or less salient of the two might not acquire any associative strength. That is, when tested in isolation, only the potent stimulus reveals conditioning ( Kamin, 1969; Mackintosh, 1971; Pavlov, 1927). The weaker stimulus is said to be overshadowed ( Pavlov, 1927) by the stronger one.

Address correspondence to Marlies Pinnow, Ruhr-University Bochum, Faculty of Psychology, Postbox 10 21 48, 44721 Bochum, Germany.

A selective attention model (see Mackintosh, 1975) might explain this effect.

In food-aversion learning of rats, a new taste seems to be the most potent
stimulus for aversive conditioning ( Nachman, Rauschenberger, & Ashe, 1977).
However, contradictory results have been reported for the interaction between
taste and odor when both are presented together. Garcia and his associates, for
example, have shown that the conditioning of the normally less potent odor stimu­
lus is facilitated by a taste when both taste and odor are presented simultaneously
( Lett, 1984; Palmerino, Rusiniak, & Garcia, 1980; Rusiniak, Hankins, Garcia, &
Brett, 1979; Rusiniak, Palmerino, & Garcia, 1982; Rusiniak, Palmerino, Rice,
Forthman, & Garcia, 1982). Although such taste-odor potentiation has been ob­
served in other laboratories as well (see Durlach & Rescorla, 1980; Kucharski &
Spear, 1985; Miller, McCoy, Kelly. & Bardo, 1986; Westbrook, Homewood,
Horn, & Clarke, 1983), the generality and robustness of this finding has been
questioned because the opposite effect, the overshadowing of a new odor by a
new taste, has also been reported ( Bouton & Whiting, 1982; Mikulka, Pitts, &Philput, 1982).

Several explanations for these contradictory results have been discussed in the literature. The conditions under which potentiation rather than overshadowing
in an odor-taste compound occurs are not clear at the moment, however. Experi­
ments have differed in several procedural parameters, but none so far has isolated
any single crucial factor (see Bouton, Jones, McPhillipps, & Swartzentruber,
1986; Bouton & Whiting, 1982; Coburn, Garcia, Kiefer, & Rusiniak, 1984; Westbrook
et al., 1983). Bouton et al. ( 1986), for example, found that an odor mixed
with a fluid–a drink odor–strongly conditioned an aversion when presented
alone but was overshadowed when the odor was mixed with a novel taste. When
the odor was presented in an odor cup surrounding the drinking spout, however,
the conditioning effect of the odor was potentiated by a new taste.

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