Responses of awake and
asleep 3-day-old human neonates were recorded to
the presentation of artificial (
vanillin,
butyric acid, formula milks) and biological (
breast milk,
amniotic fluid)
odorants matched on subjective
intensity and
trigeminal dimensions. The responses included behavioral (
facial and oral movements) and autonomic (respiration, differential
skin temperature) measures. The neonates reacted with significant
facial and
respiratory changes to low concentrations of
olfactory stimuli during the various behavioral states. The analysis of olfacto-facial configurations revealed that behavioral markers of disgust (nose wrinkling,
upper lip raising) discriminated between some
odors judged as being pleasant and
unpleasant by adult raters (
vanillin vs.
butyric acid). However, although some early predisposition to process the affective significance of stimuli may be suggested, no convincing evidence was obtained that neonates discriminated the hedonic valence of
odors within the same
perceptual space as adults. Finally, neonates evinced a differential pattern of
respiratory responding to
the presentation of milk
odors according to the mode of feeding (
breast vs. bottle feeding), suggesting that early
olfactory discrimination may be mediated by stimuli with high ecological salience.
