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.

The first unit of phonological organization is the word, with emergent control of component phonetic gestures. Long before the segment functions in speech production, the child must find a systematic way to maximize output while using a minimum of gestural schemata. The emergence of such organization may promote lexical expansion, or, instead, the pressure of accumulating word storage may trigger the initial organization. This study focuses on the origins of systematization in early word phonology. Analysis of the first 30–50 words of children acquiring five languages reveals the following two strategies. I. Controlled expansion: Constraints on production patterns are gradually relaxed, with a parallel broadening of attempted adult word shapes. Relational rules emerge when the relaxation of selection constraints outpaces the relaxation of production constraints. II. Crystallization: A variety of production patterns are explored; controlled selection of adult words becomes evident as the range of production patterns is reduced, combining elements of early vocal motor schemes to achieve a relatively complex production routine.

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