Does odour facilitate face learning? An Event-Related Potentials (ERP) study.

Face learning is a core social ability, but the contribution of olfactory cues to this process remains poorly understood. Building on models of auditory-visual integration in person recognition, we investigated whether an analogous Olfactory Recognition Unit (ORU) facilitates face learning. We tested if pairing odours with faces during learning enhances subsequent recognition. In Experiment 1,participants learned two identities from videos, each paired with a pleasant odour (rose or lilac).At test, recognition of the identities from highly variable images was assessed during odour re-presentation, while event related potentials (ERPs)were recorded (N250:200–400 ms;SFE:400–600 ms).Congruent trials referred to faces tested with the same odour as during learning; incongruent trials referred to faces tested with a different odour; control faces were novel identities not previously learned. Experiment 2 replicated the procedure with a larger sample of Caucasian participants, more distinctive odours (rose vs. sandalwood),and behavioural measures only. Across experiments, recognition was superior for learned versus control faces, confirming robust learning. In Experiment 1,this was accompanied by neural learning effects, but the N250 effect was specific to the incongruent condition and was not found for the congruent condition, which might suggest a unique modulatory role for congruent odour on early neural responses. However, there was no reliable difference in recognition or ERP amplitudes between
congruent and incongruent conditions in Experiment 1 and 2 .A trend toward higher recognition for congruent faces in Experiment 2 did not survive correction for multiple comparisons. Thus,we found no robust behavioural or neural evidence that odour congruency facilitates face learning. An interaction between ethnicity and learning condition was observed in the ERP data: Caucasian participants showed N250 and SFE learning effects, whereas Asian participants did not. This may reflect different encoding strategies for
other-race faces. Overall, these results do not support the hypothesis of an Olfactory Recognition Unit. Future studies should use natural body odours, include a no-odour control condition, and use larger samples to determine whether olfactory cues can ever become
functionally significant for person recognition.