Comparison of models of odor interaction.

Subjects rated the overall perceived intensity of concentrations of the odorants cineole, geraniol, hexyl salicylate, and linalyl acetate smelled alone and in binary mixtures. The subjects also rated intensity of specified constituents (e.g. amount of cineole in cineole, and in mixtures of cineole and linalyl acetate). The intensity of the stronger component alone offered a close description of perceived intensity. In addition to the Stronger Component model, two other psychological models (Vector and U model) and two psychophysical models (UPL2 and Equiratio Mixture model) offered descriptions ranging from fair to very good. Psychological models gave better fits, but lack explanatory power. Some results indicated that weaker odors add more potently than stronger odors, an outcome incompatible with these models. The psychophysical models, based on the additivity of single components, generally overestimated perceived intensity. Judgments of individual qualities gave only slight encouragement to any expectation of differences in masking or maskability among odorants. The results highlight the need to test particular critical hypotheses regarding how people perceive mixtures.