The nature and origin of cross-modal associations to odours

Several studies have demonstrated reliable cross-modal associations between odours and various visual, auditory, taste, and somatosensory attributes. How these associations arise is not well understood. We examined whether cross-modal associations to odours themselves form distinct groups, and whether these groupings relate to semantic (nameability, familiarity) and perceptual (intensity, irritancy, and hedonics) olfactory attributes. Participants evaluated 20 odours, varying in all of the latter attributes, and reported their visual, auditory, gustatory, and somatosensory associations for each. Significant inter-rater agreement was observed for all modalities except audition, and responses in all modalities were consistent with those obtained on a repeat test session 2 weeks later. Two groups of cross-modal odour associates emerged: one of which was related to the semantic attributes of odours and another which related to their perceptual attributes. The exception was taste, which was significantly associated with both. While these results suggest that both semantic and perceptual mechanisms underpin odour cross-modal matches, the data also point to the importance of hedonics as a further contributing mechanism.