Congruency of multisensory olfactory stimuli.

We perceive our environment via different sensory channels in a multisensory fashion. During multisensory integration, these channels can enhance or hinder each other depending on congruency. Here, we aimed to investigate how the congruency of gustatory and visual costimulation alter the perception of olfactory stimuli. We hypothesized that congruent costimulation enhances the perception of likeness, i.e. how well stimuli match a label, compared with no and to incongruent costimulation. We also aimed to quantify the effect of gustatory and visual costimulation. We tested 48 healthy young participants. We used retronasal olfactory stimuli (strawberry, cheese, lemon, and coffee) (i) alone or with congruent/incongruent costimulation ((ii) with congruent gustatory (sweet, salty, sour, and bitter), (iii) with congruent visual (images of strawberry, cheese, lemon, and coffee), (iv) with congruent visual and gustatory, (v) with congruent visual and incongruent gustatory, (vi) with congruent gustatory and incongruent visual, (vii) with incongruent visual and gustatory costimulations). Olfactory and gustatory stimuli were presented by means of droplets on the tongue, i.e. olfactory stimuli were delivered retronasally, while visual stimuli were presented on a computer screen. We asked participants to evaluate the solutions' likeness to the respective olfactory label on visual analog scales. We observed a significant effect of congruency on likeness (P < 0.001). Gustatory costimulation had a significantly stronger effect than visual costimulation (P = 0.02). Congruent costimulation enhances the evaluation of likeness while incongruent costimulation reduces it, with gustatory costimulation having significantly stronger effects than visual costimulation. This could be useful in multisensory olfactory training paradigms for olfactory loss.