In Experiment 1, some odorous solutions (e.g., strawberry) were rated as smelling stronger when colored (e.g., red) than when colorless. Experiment 2 showed this effect to be due to a perceptual change rather than a response to experimental demand characteristics. Experiment 3 showed that the color-induced increase in odor intensity is not due to subjects' preexperimental experience with particular color-odor combinations, because the increase occurred with novel ones. We conclude that color induces a weak olfactory percept that combines with odorant-induced percepts. The effect may be due to conditioning or may be the result of residual intersensory neural connections left over from infancy.
The effects of color on odor identification were tested under color appropriate, inappropriate, and blindfolded conditions. Subjects made fewer errors in identifying solutions that were colored appropriately (e.g., red-cherry) than in either the blindfolded condition, where there were no color cues, or the inappropriate color condition (e.g., red-lemon). Identification accuracy was greatest for typical odor-color combinations (e.g., red-cherry) compared with appropriate but nontypical odor-color combinations (e.g., red-watermelon). Response latencies were fastest for odors in the appropriately colored solutions. Subjects also rated appropriate color-odor combinations as most pleasant. However, this effect is probably due to the increase in identification accuracy of the appropriately colored solutions. In all three conditions, correctly identified odors were liked more than odors that were not correctly identified. Thus, color is an important perceptual variable in odor identification because it biases subjects toward a color category that facilitates identification if the color is "correct". This ability to identify an odor in turn influences the affective response to the odor.
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