Introduction

Despite the fact that they are produced in different modalities, gesture and speech form a unified communication system in adults. To explore whether symbolic communicative gesture and speech form a single system in young children, three girls and three boys were observed longitudinally during the transition from one- to two-word speech. Initially, gesture tended to be produced without speech, and, on the rare occasions when it was combined with speech, that speech was meaningless and not synchronized with the accompanying gesture. The two characteristics that define integration in adult speakers – semantic coherence (combining gesture with meaningful and related speech) and temporal synchrony (producing gesture in synchrony with speech) – were found to emerge in the children's communications at the same moment and prior to the onset of two-word speech. The onset of gesture–speech integration thus occurs during the one-word period and before words are combined with other words.

Adults and children typically express their thoughts in speech, and, along with that speech, they spontaneously produce gestures. Despite the fact that they are produced in different modalities, gesture and speech deliver a coherent message to the listener (Alibali, Flevares & Goldin-Meadow 1997; Goldin-Meadow & Sandhofer 1999; Goldin-Meadow, Wein & Chang 1992; McNeill, Cassell & McCullough 1994) and thus can be said to form a single unified communication system (Goldin-Meadow 1997; Goldin-Meadow, Alibali & Church 1993; McNeill 1985, 1992).