Statistical evidence that a child can create a combinatorial linguistic system without external linguistic input: Implications for language evolution


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Abstract

HighlightsTo determine language-learning biases, we study a child with no linguistic input.A deaf child who acquired no spoken language and was not exposed to sign language.The child used gestures–called homesigns–to communicate.We apply a stringent statistical test to homesign and find it to be combinatorial.Its grammar generates an unbounded number of expressions, the hallmark of language.Can a child who is not exposed to a model for language nevertheless construct a communication system characterized by combinatorial structure? We know that deaf children whose hearing losses prevent them from acquiring spoken language, and whose hearing parents have not exposed them to sign language, use gestures, called homesigns, to communicate. In this study, we call upon a new formal analysis that characterizes the statistical profile of grammatical rules and, when applied to child language data, finds that young children’s language is consistent with a productive grammar rather than rote memorization of specific word combinations in caregiver speech. We apply this formal analysis to homesign, and find that homesign can also be characterized as having productive grammar. Our findings thus provide evidence that a child can create a combinatorial linguistic system without external linguistic input, and offer unique insight into how the capacity of language evolved as part of human biology.

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