Odours alter evaluations of concurrent visual stimuli. However, neural mechanisms underlying the effects of congruent and incongruent odours on facial expression perception are not clear. Moreover, the influence of emotional faces on odour perception is not established. We investigated the effects of one pleasant and one unpleasant odour paired with happy and disgusted faces, on subjective ratings and ERP responses to faces.
Participants rated the pleasantness of happy and disgusted faces that appeared during 3 s pleasant or unpleasant odour pulses, or without odour. Odour pleasantness and intensity ratings were recorded in each trial. EEG was recorded continuously using a 128-channel system.
Happy and disgusted faces paired with pleasant and unpleasant odour were rated as more or less pleasant, respectively, compared to the same faces presented in the other odour conditions. Odours were rated as more pleasant when paired with happy faces, and unpleasant odour was rated more intense when paired with disgusted faces. Unpleasant odour paired with disgusted faces also decreased inspiration. Odour-face interactions were evident in the N200 and N400 components.
Our results reveal bi-directional effects of odours and faces, and suggest that odour-face interactions may be represented in ERP components. Pairings of unpleasant odour and disgusted faces resulted in stronger hedonic ratings, ERP changes, increased odour intensity ratings and respiratory adjustment. This finding likely represents heightened adaptive responses to multimodal unpleasant stimuli, prompting appropriate behaviour in the presence of danger.