Grunt communication in human infants (Homo sapiens).

Laryngeally produced vocalizations termed grunts function communicatively in many species. The vocalizations and accompanying behavior of 5 human infants videorecorded monthly at the transition to speech were analyzed to determine the frequency, physiological basis, and functional status of grunt production, a phenomenon systematically studied for the first time here. Earliest grunts occurred accompanying movement or effort; next, they accompanied acts of focal attention; and finally they were used in communication. Communicative use was followed by the onset of referential ability in language. This sequence is interpreted in relation to the physiological basis of these vocalizations in respiratory function and to additional developmental variables observed in the children. The findings have implications for the transition to the communicative repertoire in other species in which laryngeal function contributes to communication.