Abstract How children acquire their L1 has been predicted and explained under different hypotheses. One is the independence hypothesis [1] and the other is the hypothesis of early interaction [2]. The former claimed that L1 development is constrained by biological maturational processes, with no link to perceptual mechanisms, that is, language development is independent of linguistic environment. The latter was that perceptuo-motor attunements already operate in L1 development, so the ambient and environmental effects can be traced from an early age. Our study attempts to explore which perspective is involved in the process. We conduct an investigation on the acquisition of tone in early language development by using longitudinal data of one Mandarin-speaking child living in Changsha. The tonal acquisition process was analyzed from statistical and phonetic aspects to investigate whether Mandarin-learning infants. tonal development reflect universal or language-specific effects. Our findings reveal that the infant gains a full mastery of tone system of Mandarin till she grew to two years old, or even four months later. Also, as the subject gets more exposure to her mother tongue, her tone production gets approaching to adults., which indicates the effect of ambient language. All these lend adequate support for the hypothesis of early interaction.

Index Terms: tone acquisition, children under three, southern Mandarin, the hypothesis of early interaction

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