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RESEARCH PRODUCT

When your nose knows what you see : multisensory development of visual categorization : evidence from odor-driven face categorization in the human brain

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This thesis examines whether and how odors contribute to the development of visual categorization in the human brain using fast periodic visual stimulation coupled with scalp electroencephalography (FPVS-EEG). Specifically, we sought to characterize if a neural visual response selective to the face category is modulated by the presence of a body odor in both infants (Study 1, 2, 3) and adults (Study 4).In infants, the selectivity of the odor effect on visual categorization was addressed by testing separately three categories in three groups of 4-month-old infants presented with a control odor or their mother’s odor. We observed that a face-selective response is largely enhanced by maternal odor over the right occipito-temporal cortex (Study 1). By contrast, a car-selective response, observed over the right occipital region, is insensitive to the presence of maternal odor (Study 2). Finally, when using nonface objects configured as faces (i.e., facelike objects), a facelike-selective response is amplified over the right hemisphere when infants are exposed to maternal odor, and even initiated in some infants who do not selectivly respond to facelike objects in the absence of maternal odor (Study 3). In adults, the selective responses to human faces, cars and facelike objects were recorded in a body, gasoline, or control odor context (Study 4). While the categorization of human faces or cars is immune to the presence of odors, the body odor enhances the facelike-selective response, suggesting a facilitating effect of a congruent odor when the visual categroy is ambiguous. For these four studies, the general visual response elicited by all stimuli in the rapid visual sequence remains stable across odor contexts, excluding any general effect of odors in terms of arousal/attention.Altogether, these findings demonstrate a strong facilitative effect of body odors on congruent visual categorizations (i.e., human or illusory faces). We thus illustrate through olfactory-visual associations that information from different senses are integrated to facilitate visual categorization, especially early in life when the visual system is still immature, and that these intersensory congruent associations are maintained until adulthood in the case of ambiguous visual stimuli.