Taste of breath: the temporal order of taste and smell synchronized with breathing as a determinant for taste and olfactory integration.

Many studies have reported that subjective taste intensity is enhanced by odors which are congruent, for example a sweet taste and a vanilla odor. Some reports have suggested that subjective taste is more strongly enhanced by retronasal than by orthonasal odors; others have suggested that taste enhancements by both odor routes are identical. Differences between the two routes include the direction of airflow accompanying breath. Thus, it is possible that the order of gustatory and olfactory stimuli when breathing through either route while drinking is a determining factor for taste-odor integration. To reveal the natural relationship between taste intensity enhancement by odors and breath, synchronization of odor stimulation with the breath is necessary. Here, we examined whether the enhancement of a sweet taste is induced by a vanilla odor presented in various combinations of odor routes, immediately before and immediately after drinking. The results showed that a retronasal odor after drinking enhanced taste, but an orthonasal odor before drinking did not. The retronasal odor before drinking and the orthonasal odor after drinking did not enhance the sweet taste. These results show that congruency with the natural order of stimulus and kinetic sensation is a determining factor for odor-induced taste enhancement.