Maternal odor selectively enhances the categorization of face(like) stimuli in the 4 month-old infant brain

Présentation PosterInternational audienceIn the 4-month-old infant brain, the visual categorization of natural face images is enhanced by concomitant maternal odor (Leleu et al., 2019), providing support for the early perception of congruent associations between co-occurring inputs from multiple senses. Here, we further explore whether this maternal odor effect is selective to faces or if it can be explained by a more general influence of salient odor cues on the perception of any visual object category. In Experiment 1, scalp electroencephalogram was recorded during a fast periodic visual stimulation (FPVS-EEG) while 4-month-old infants were exposed to the maternal vs. a control odor. In rapid 6-Hz streams of natural images (i.e., 6 stimuli per second), images of cars instead of faces were interspersed every 6th stimulus among other nonface objects (i.e., at 1 Hz). We isolated a neural categorization response to cars at the predefined 1-Hz frequency over the right occipital region in both odor contexts, showing the ability of infants to categorize variable exemplars of cars at a glance. However, maternal odor did not enhance this response, supporting its face-selective influence. In Experiment 2, images of nonface objects resembling faces (i.e., facelike stimuli) were used as the target category, i.e., interleaved every 6th image in the stream of stimulation. The brain response to facelike objects was faint yet clearly identifiable over bilateral occipito-temporal sites in the control odor condition, revealing infants' sensitivity to facelike patterns in a fast train of various categories of living and nonliving objects. More importantly, we observed that maternal odor magnified the facelike categorization response over the right hemisphere in a majority of infants, showing that this highly relevant odor triggers a face-selective neural activity even in the absence of genuine human faces. In both experiments, the general visual response elicited by the rapid 6-Hz stimulation was immune to the maternal odor effect, excluding any account in terms of an undifferentiated increase of visual attention or arousal in the maternal odor context. Altogether, these experiments provide evidence for the tuning of face(like) categorization from multisensory inputs in the developing brain. They accord with the view that perceptual development integrates information across the senses for efficient category acquisition, with early-maturing systems, such as olfaction, providing assistance to later-developing systems, such as vision