The decline of cross-species intersensory perception in human infants.

Between 6 and 10 months of age, infants become better at discriminating among native voices and human faces and worse at discriminating among nonnative voices and other species' faces. We tested whether these unisensory perceptual narrowing effects reflect a general ontogenetic feature of perceptual systems by testing across sensory modalities. We showed pairs of monkey faces producing two different vocalizations to 4-, 6-, 8-, and 10-month-old infants and asked whether they would prefer to look at the corresponding face when they heard one of the two vocalizations. Only the two youngest groups exhibited intersensory matching, indicating that perceptual narrowing is pan-sensory and a fundamental feature of perceptual development.