Influence of simultaneous gustatory stimuli on orthonasal and retronasal olfaction

Orthonasal and retronasal olfaction processes differ. The aim of this study was to examine whether congruent and incongruent simultaneous gustatory stimuli influence orthonasal and retronasal odorant perception, using olfactory event-related potentials as a measure. Thirty-two young, healthy subjects (16 men, 16 women) took part in two test sessions. Olfactory event-related potentials were recorded in response to a food-like odor, vanillin, and to an odor usually not associated with foods, the rose-like phenylethylalcohol. Each session consisted of four randomized blocks of 15 stimuli each which were applied either orthonasally or retronasally. Simultaneously, sweet or sour gustatory stimuli were applied. In response to retronasal vanillin, stimuli latencies P2 of the event-related potentials were significantly shorter in the congruent "sweet condition" than the incongruent "sour condition". In contrast, with orthonasal stimulation, shorter P2 latencies were seen for both odorants in the incongruent condition. Intensity of both odorants was perceived as less pronounced after retronasal stimulation than after orthonasal stimulation. In conclusion, application of a sweet taste significantly enhanced the processing of a congruent olfactory stimulus when presented through the retronasal route. Incongruent simultaneous gustatory stimulation applied during orthonasal olfaction seemed to induce conflict priming, also resulting in faster processing.