Conceptual processing of natural, complex odours: multisensory effects on behaviour and ERSP

We encounter our environment in a multisensory way, yet little is known about the processing of olfactory stimuli within a visual context. In this study, we investigated the effects of visuo-olfactory congruency on associated Event-Related Spectral Perturbations in the electroencephalography signal and pleasantness/intensity ratings. We presented pine wood odour or clean air with congruent or incongruent pictures to 21 participants. Olfactory processing manifested in an increase in delta band power, decrease in alpha band power, and higher intensity ratings. We further observed alpha band desynchronisation while attending concept-relevant pictures and an effect on pleasantness. There was also a conceptual effect on late delta band power, which may reflect increased processing needs for incongruent visuo-olfactory information. A second, independent experiment (n = 21), using citral as odour stimulus, ruled out that these effects were merely processing of simultaneous olfactory and visual stimulation, but likely to be processing on a conceptual level.