Academic journal article The Psychological Record

Perceptual and Physical Properties of Reward and Nonreward Odors

Academic journal article The Psychological Record

Perceptual and Physical Properties of Reward and Nonreward Odors

Article excerpt

Two types of questions might be asked about reward and non reward odors as stimulus events for the rat. First, how does the rat perceptually categorize and organize these odors? When the rat is asked to differentiate odors arising from reward and nonreward goal events, what can its behavior tell us about its perception, assuming it responds differentially to the odors? Clearly rats can tell the difference, because odors arising from reward and nonreward goal events differentially control unlearned reactions (e.g., Collerain, 1978; Collerain & Ludvigson, 1972, 1977; Mellgren, Fours, & Martin, 1973) and provide a basis for acquiring a discrimination in an instrumental learning task (e.g., Eslinger & Ludvigson, 1980a; Ludvigson & Sytsma, 1967; Morrison & Ludvigson, 1970; Seago, Ludvigson, & Remley, 1970; Taylor & Ludvigson, 1987). But, are odors associated with reward and non reward both perceived as different from the characteristic odor of a rat? Are there perceived similarities in reward and non reward odors? Do they smell different by a matter of degree (i.e., quantitatively) or essence (i.e., qualitatively)? These are not easy questions to answer, and the search for answers is far from complete, but the questions have helped to focus attention on the odorants as significant perceptual events in the rat's life.

A second type of question may be asked, not independent of the first, and addressed in part through behavioral inferences as well. What are the physical properties of the relevant odorants? Are they continuously dispersed as the rat moves around during or after experiencing reward or nonreward, or is there a brief but concentrated emission? Does the same odor accumulate across different rats experiencing the same event? Do the odors adhere to surfaces of an environment where a rat experiences reward or nonreward, or are they airborne? Are they low or high in volatility?

Evaluating such properties of the odorants is a crude business at best when relying on behavioral inferences, but even such indirect inferences provide a preliminary step toward identifying and characterizing the odorants' chemical composition. Perhaps more importantly, understanding such properties is potentially relevant to issues of behavioral and ecological significance of the odorants and odor production. For example, Smith (1977) indicates that in social insects, alarm pheromones are more volatile, and diffuse farther and faster, than either trail pheromones or pheromones which serve to identify species or group membership. Although this is not to suggest that what is true for social insects should be true for rats, nor that reward odor or nonreward odor can be appropriately considered pheromonal, it is clear that in the animal world there is a correspondence between functional and physical properties of naturally occurring odorants. This paper addresses the questions of perceptual differences and physical properties of reward and nonreward odors separately, then considers the relationship between the two.

Some Preliminary Considerations

A Perceptual Approach: Stimulus Centered

A perceptual approach to the phenomenon of reward and non reward odors is stimulus centered, in contrast to approaches which emphasize mechanisms of action or implications for response tendencies. If we imagine a simple hypothetical diagram of most behavioral phenomena, it might look something like the following:

Stimulus Representation [right arrow] Processing "Decision Making"] [right arrow] Response [Initiation]

Although the three components represented in this diagram are overlapping, interrelated, and not clearly separable, a perceptual approach could be considered one in which behavioral variability due to the response and processing components is minimized whereas variability due to the stimulus component is maximized (Arnoult, 1967). For present purposes, the diagram looks as follows:

Odorant Representation [right arrow] Retrieval of learned/unlearned associations [Assessing "Meaning"] [right arrow] Differential Response

In the work discussed here, processing demands are characteristically minimized: Either the rats can utilize readily available response tendencies, or, if learning is required, reward contingencies are simple. …

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