Different Olfactory Percepts Evoked by Orthonasal and Retronasal Odorant Delivery

The Duality of Smell hypothesis suggests odorants delivered orthonasally elicit different sensations compared with those delivered retronasally despite activating the same receptors in the olfactory epithelium. Presently, we investigated this further using a matching paradigm free from odorant or semantic memory bias. Subjects were asked to evaluate an aroma delivered in one condition (orthonasal or retronasal delivery) and match the same aroma from 4 unknowns evaluated in the same or different delivery conditions. Panelists matched flavors in 4 delivery conditions: orthonasal-orthonasal, retronasal-retronasal, retronasal-orthonasal, and orthonasal-retronasal. For orthonasal presentation, panelists smelled samples using their nostrils, and for retronasal presentation, panelists swallowed aqueous flavors. In Experiment 1, panelists were instructed to match familiar flavors (banana, grape, orange, raspberry). In Experiments 2 and 3, panelists used the same experimental design with either 4 unfamiliar flavors (kinnow, longan, pawpaw, prunus) or 4 distinct subtypes of a strawberry flavor (woody, green, ripe, candy). In Experiment 1, the number of correct matches in each condition did not significantly differ suggesting stability in the perceptual construct across delivery routes. However, in Experiments 2 and 3, significantly more samples were correctly matched in the orthonasal-orthonasal and retronasal-retronasal conditions compared with the retronasal-orthonasal or orthonasal-retronasal conditions suggesting aroma perception is dependent on delivery route. Additionally, across the 4 delivery methods, the ability to correctly match flavors decreased as flavor familiarity decreased or similarity increased and may reflect the different cognitive strategies employed by subjects when matching these stimuli. Our results suggest odorant percepts are route-dependent and consistent with the Duality of Smell phenomenon.