Hemispheric asymmetries in adults' perception of infant emotional expressions.

Accounts of emotion lateralization propose either overall right hemisphere (RH) advantage or differential RH versus left hemisphere (LH) involvement depending on the negative-positive valence of emotions. Perceptual studies generally show RH specialization. Yet viewer emotional responses may enhance valence effects. Because infant faces elicit heightened emotion in viewers, perceptual asymmetries with chimeric infant faces were assessed. First, it was determined that chimeras must be paired with their counterparts, not their mirror images, to tap viewers' sensitivity to adult facial asymmetries. Results showed an RH perceptual bias for infant cries but bihemispheric sensitivity to asymmetries in infant smiles. This effect was not due to LH featural versus RH holistic processing and held for additional, intensity-matched, spontaneous expressions. Specialized RH sensitivity to infant cries may reflect an evolutionary advantage for rapid response to infant distress.