Behavior and alpha-band oscillations reveal cross-modal interactions between chemosensory and auditory processing

The perceived location of a sound can be mislocated towards a spatially discordant but temporally synchronous visual stimulus. This is referred to as the spatial ventriloquist effect. However, whether chemosensory cues can similarly bias sound localization remains largely unaddressed. Hence, the present EEG study adopted a dynamic sound localization paradigm with concurrent bimodal odorant stimulation. Participants heard sequences of sounds varying in location. After each sound, participants made a two-alternative forced choice localization judgment (left vs. right). Critically, in a subset of occasions, but unbeknown to the participants, the sounds originated from a central location. Furthermore, in the first half of the sequence, sound presentation could be accompanied by a task-irrelevant, trigeminally potent odorant in the left, right, or both nostril(s). Auditory-only trials and birhinal stimulation served as controls. For central sounds in the second half of the sequence, the proportion of right-ward responses increased with right-nostril stimulation but decreased with left-nostril stimulation relative to the control conditions, showing an after-effect of odorant stimulation for ambiguous sound cues. This odorant-induced localization bias diminished with increasing spatial discernability of the sounds. On the contrary, alpha power lateralization, a correlate of auditory spatial attention, was most susceptible to odorant stimulation when the spatial disparity between the senses was largest, as reflected in diminished alpha lateralization for incongruent chemosensory-sound stimulation. No such effect was present in a multivariate decoding analysis of alpha power. We discuss the present findings in light of cross-modal interactions and a proposed common attentional control system between the senses.