Dissimilarity of blending mixture and components in an olfactory space

Certain odour mixtures appear processed differently from their components at the glomerular level (Grossman et al., 2008). Such results could support the idea of odour mixture configural perception, a concept which is much likely to occur in multicomponent mixture (Jinks et al., 2001). In the present study we evaluated whether human subjects perceived a 6 components odour mixture, previously suspected to produce a blending effect in human adults (Le Berre et al., 2008; and in rabbit pups, Sinding et al., ECRO 2010), as different from its components, by an approach representing the olfactory space of a mixture mainly focused on aromatic qualities similarities. Our hypothesis is that the blending, occurring when subjects perceive an odour quality specific to the mixture and not to the components, is represented by a novel quality well separated from each one of the components in an olfactory space. Seventy three human subjects carried out a free-sorting task on 7 stimuli (mixture and the 6 components) delivered in glass bottles. The data were analysed through a non-metric MDS followed by a bootstrap analysis in order to create a map of similarity of the stimuli and confidence ellipses around each stimulus on the map. The results clearly indicated that the mixture was significantly separated from each of its components. Moreover the mixture is not located in the barycentre of the space and is not surrounded by the components. Thus, the odour perceived by the subjects exposed to the mixture does not appear to result from the summation of components’ qualities or from a mix up of the numerous components. It would result from the perception of a new, unique and distinct odour quality, promoted by the association of the 6 components in specific proportions.