Even at 4 months, a labial is a good enough coronal, but not vice versa.

Numerous studies have revealed an asymmetry tied to the perception of coronal place of articulation: participants accept a labial mispronunciation of a coronal target, but not vice versa. Whether or not this asymmetry is based on language-general properties or arises from language-specific experience has been a matter of debate. The current study suggests a bias of the first type by documenting an early, cross-linguistic asymmetry related to coronal place of articulation. Japanese and Dutch 4- and 6-month-old infants showed evidence of discrimination if they were habituated to a labial and then tested on a coronal sequence, but not vice versa. This finding has important implications for both phonological theories and infant speech perception research.