Establishing an "affective scale" for odor preferences of infant rats.

To establish an "affective scale" for odor preferences, the scale must indicate aversion as well as attraction to odors. Because the construction of preference scales requires repeated tests with a set of odors, and because exposure to aversive odors may lead to a reduction in the aversiveness of these odors, the effects of repeated exposure to an aversive odor (peppermint) on preferences for this odor were examined. Eighteen-day-old Long-Evans rats were given three preference tests using all pairs of three odors: unscented pine shavings (N), own maternal odors (M), and peppermint odors (P). Before these tests rats were exposed to the test arena and unscented pine shavings or peppermint odor for 0, 1, or 4 days. All rats showed an attraction to their maternal odor and an aversion to peppermint odor, showing the preference scale M greater than N greater than P. Preexposure to peppermint in the test apparatus only slightly reduced the aversion to peppermint odor. The results indicate that scaling procedures will accurately detect odor aversions as well as attractions and that the preference scales are only slightly altered by repeated exposure to odors during the testing period.