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 aim to investigate how the congruency of gustatory and visual co-stimulation alter the perception of olfactory stimuli. We hypothesize that congruent co-stimulation will enhance the perception of likeness, i.e., how well stimuli match a label, compared to no and to incongruent co-stimulation. We also aim to quantify the effect of gustatory and visual co-stimulation. We tested 48 healthy young participants. We used retronasal olfactory stimuli (strawberry, cheese, lemon, coffee) (1) alone or with congruent/incongruent co-stimulation ((2) with congruent gustatory (sweet, salty, sour, bitter), (3) with congruent visual (images of strawberry, cheese, lemon, coffee), (4) with congruent visual and gustatory, (5) with congruent visual, incongruent gustatory, (6) with congruent gustatory, incongruent visual, (7) with incongruent visual and gustatory co-stimulations). 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 analogue scales. We observed a significant effect of congruency on likeness (p < .001). Gustatory co-stimulation had a significantly stronger effect than visual co-stimulation (p = .02). Congruent co-stimulation enhances the evaluation of likeness while incongruent co-stimulation reduces it, with gustatory co-stimulation having significantly stronger effects than visual co-stimulation. This could be useful in multisensory olfactory training paradigms for olfactory loss.