Infants’ hedonic responsiveness to food odours: a longitudinal study during and after weaning

Background: Olfaction is a highly salient sensory modality in early human life. Neonates show keen olfactory sensitivity and hedonic responsiveness. However, little is known about hedonic olfactory responsiveness between the neonatal period and 2 years of age. In an attempt to fill this gap, this longitudinal follow-up study aimed at investigating hedonic responses to food odours in infants during the first 2 years of life. The second objective was to evaluate whether gender has an influence on hedonic responses during this early period. Four control stimuli and eight odours (four rated by adults as a priori pleasant and four a priori unpleasant) were presented in bottles to 235 infants at 8, 12 and 22 months of age. The infant’s exploratory behaviour towards odorized and control bottles was measured in terms of mouthing defined as direct contact with perioral and/or perinasal areas. For each odorized bottle, duration proportions of mouthing were calculated relative to the control bottles. Results: For the three ages, shorter duration of mouthing was found for unpleasantly scented bottles compared to pleasantly scented bottles. This contrast between pleasant and unpleasant odours was similar for girls and boys. Correlations of responses between ages were modest in number and level, and concerned mostly unpleasant odours. Conclusion: During the first two years of life, infants discriminate the hedonic valence of odours. They avoid most of the food odours considered as unpleasant by adults, but their attraction towards food-odours judged pleasant by adults does not appear to be fully shaped at this early age. Taken as a whole, the present results highlight both the plasticity of hedonic responses to food odours, and relatively stable avoidance behaviours towards some unpleasant odours.