One major unresolved problem in olfaction research is to relate the percept to the molecular structure of stimuli. The present study examined this issue and showed for the first time a quantitative structure-odor relationship in which the more structurally complex a monomolecular odorant, the more numerous the olfactory notes it evokes. Low-complexity odorants were also rated as more aversive, reflecting the fact that low molecular complexity may serve as a warning cue for the olfactory system. Taken together, these findings suggest that molecular complexity provides a framework to explain the subjective experience of smells.

One important aspect of odor hedonics is its plasticity during human development. The present study set out to probe the modulators of such olfactory change during that period by testing the hypothesis that language and semantic representations of objects are strong organizers of odor liking. To this end, 15 three-year-old children were tested in a longitudinal study. Participants were exposed to exactly the same 12 odorants once a year over a 3-year period. At each experimental session, they were asked to answer 2 questions: 1) "Do you like or dislike this odor?" and 2) "Can you tell me what it is?" The level of language production was assessed on a standardized test. The 3-year-old children were found to categorize the same number of odorants as liked and as disliked. The follow-up study, in contrast, showed that at 5 years of age they categorized more of these odors as liked and that the shift was significant only in the children with higher language production skills. Taken as a whole, these findings suggest that the 3- to 5-year age range, when children begin to master language, is a turning point in the construction of olfactory hedonic categories during childhood.