An oral-cavity component in retronasal smelling of natural extracts

Abstract Retronasal and oral-cavity-only identifications of six natural extract odorants, presented in air-phase, were compared in an initial experiment. Prior to identification testing, the 21 participants were given experience with air-phase presentations, and with the odorants and their correct identifications. Retronasal correct identifications for anise, cinnamon, coffee, orange, peppermint, and strawberry were 88%, 81%, 98%, 95%, 91%, and 83%; oral-cavity-only, 19%, 21%, 19%, 21%, 33%, and 24%. All participants correctly identified retronasal odorants above chance. Across participants only peppermint received correct oral-cavity-only identifications, but two participants gave correct oral-cavity-only identifications for all odorants. In a second experiment, different participants attempted to discriminate oral-cavity-only odorants from their solvents. Fifteen participants discriminated orange, peppermint, and strawberry odorants from their solvents, and five discriminated all odorants from their solvents. It had been hypothesized that peppermint would provide unique trigeminal stimulation; this was supported by correct oral-cavity-only identification of only peppermint. A second hypothesis posited oral-cavity-only discrimination of orange and peppermint from their solvents because of trigeminal stimuli, but strawberry extract discrimination was unexpected. Furthermore, oral-cavity-only discrimination of all odorants by one-quarter of the participants was not anticipated. Overall, these outcomes suggest that peppermint-like odorants can initiate sufficiently differential responses in the oral cavity to permit identification, indicate that not only odorants with known trigeminal stimulus components but also others may elicit oral-cavity-only air-phase responses, and imply that for a substantial minority of individuals, trigeminal input may enhance oral-cavity effectiveness of many odorants during retronasal smelling.