Features of infant sounds: the emergence of cooing

Vocalizations of two female infants, recorded over a 5-week period after the first emergence of cooing, were studied. The vocalizations were classified as cry, discomfort, vegetative and cooing (comfort) sounds. Fifty vocalizations of each sound type, distributed across the 5-week period of study, were selected from the output of each infant (400 vocalizations in all). The features of voicing, breath direction and consonant-like versus vowel-like were documented for each sound type. It was found that the features of the more primitive sound types regrouped themselves in comfort sounds. For the first time the feature of consonant-like was found to co-occur with voicing and egressive (outgoing) breath direction. The implications for theories of pre-speech development are discussed.