Perceptual interactions in odour mixtures: The blending effect
Résumé
The odour perceived from a mixture of odorants varies depending on several factors as the context, individual physiological abilities, experience… but also as the perceptual interactions occurring over the processing of odorant mixtures. Sometimes, these interactions which appear during odour information coding and processing, lead to synergy or masking of odour notes (1). In other occasions, they lead to a blending effect. Odour blending appears when a mixture is perceived as a unique odour different from the odour of its components (1, 2). This type of mixture is well known by perfumers and flavourists who daily construct and use it in an empirical fashion. Here, we conducted a series of experiments to evaluate the contribution of two factors suspected to contribute to such a blending phenomenon, the number and the proportions of the odorants included in the mixture. We took advantage of previous results that showed, through a typicality rating test, that mixtures of 2 and 6 components were rated as more typical of a target odour than each of their components (3). In our experiments, we performed sorting and similarity tasks of several mixtures and their components in order to evaluate the perceptual qualitative distance existing between components and mixtures. We depicted the results as odour quality spaces. As a result, the binary and senary mixtures were perceived as significantly different from their components, in contrast to mixtures with same components but in different proportions and supposed to not induce a blending effect. Regarding the 6 components mixture, it was discriminated from all its components and it was interestingly not located at the barycenter of the odour quality space formed by the components. Concerning the binary mixture it was not either located in between the position of the two components in the odour quality space. This suggests that the quality of the mixture is not a mix of the qualities of the components but rather a distinct (new) one and that it is a blending effect. Complementary results on the 6 components mixture showed that the proportion of each component in the mixture is also a key factor for blending occurrence but that each component did not have the same impact on the blending effect. To conclude, some mixtures appear as inducing perceptual blending, a processing depending on specific odorants mixed in specific proportions.