Academic journal article The Psychological Record

Discussion of Section 1

Academic journal article The Psychological Record

Discussion of Section 1

Article excerpt

Despite the difficulties and limitations of studying episodic odors with behavioral techniques, intriguing inferences have emerged, along with many questions. Regarding the odor generated by reward (R odor) as against nonreward (N odor), Taylor [ILLUSTRATION FOR FIGURE 5 OMITTED] concluded they probably contain relatively volatile, qualitatively different components specific to the reward and nonreward experiences. They seem chemically stable for at least 15 min (Ludvigson, July, 1977) or longer (studies showing cumulative effects are suggestive, e.g., data from Prytula, Davis, & Fanning, 1981, suggest 20 min). In addition, both odor complexes seem to contain an otherwise less volatile "contextual" odor, characteristic of the rat rather than resulting from the rat's episodic experience, with the non reward complex containing the larger quantity of this component. Ludvigson and Duell (this issue) summarized data indicating there is more urine deposited on N than R trials, and urine could provide part of this contextual "rat" odor. However, they also pointed to several studies indicating urine odor does not control the behavioral patterning to R and N odors so often observed.

This last conclusion is not limited to patterned responding and conditions of hunger: Not heretofore mentioned, McNeese (1976) found components arising from both R odor and N odor readily served as conditioned stimuli in a conditioned suppression task, though the rats could not achieve a discrimination between them. This failure occurred despite the fact N odors "frequently contained considerable amounts of urine whereas reward samples did not and on this basis alone a discrimination might have been expected to develop, but did not" (McNeese, 1976, p. 64). In retrospect, it seems critical that McNeese's R and N odors came from runway paper flooring that was placed into a jar from which airborne materials were transported to the conditioned suppression apparatus. As Taylor (this issue) later discovered, unique odors associated with R and N experiences are difficult, if not impossible, to transport in this manner, evidently requiring more thorough capture of volatile components. However, residual urine differences remained on the papers, and one wonders why the rat did not utilize these apparent urine differences to signal the upcoming shock, assuming they were odorous. Interestingly, in contrast to the difficulty of transporting R and N odors, Williams (Section 2, this issue) readily transported odors from shock-stressed rats via movement of corncob flooring, only.

These conclusions by Taylor (this issue) and Ludvigson and Duell (this issue) concerning the nature of R and N odors agree with those by Voorhees and Remley (1981), who found differences in single-cell recordings from mitral cells in the olfactory bulb not only between N odor and R odor, but also between N odor and food and urine odors. As discussed in Ludvigson and Duell (this issue), residual food odors cannot be the source of R odor, though they might be the source of odors "motivationally specific" to conditions of hunger/food versus thirst/water.

Motivational specific effects remain an intriguing research topic, though whether they occur under incongruent conditions other than hunger/food versus thirst/water is unknown. Duell, Holcom, and Bray (1987) found no specificity effect from food pellets versus a sweet liquid of milk and sugar, when drive states of donors and test animals were congruent (hunger). That is, test animals discriminated R and N odors from donors equally well whether donors and test animals received the same or different reinforcers. Recall, a motivational specificity effect implicates two phenomena: (a) specific odors arising from donors' experiences, and (b) a "fortuitous predisposition of the rat to respond differentially to specific odors" (Ludvigson & Duell, this issue). Absence of an effect could be due to either, though one might presume any residual reinforcer traces should differ. …

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