An experimental study of Mandarin-speaking children's acquisition of recursion under a formal definition/classification system for recursion.

• The construction of a formal definition/classification system for recursion. • An experimental study of child acquisition of tail-, nested- and mixed-recursion relative clause sequences. • Different levels and subtypes of recursive sequences are acquired at significantly different ages. • The results suggest which part of Chomsky's Hierarchy is unique to language. Starting with constructing a formal definition/classification system for recursion and consequently dividing recursive sequences into different levels and subtypes, the current paper presents an experimental study of Mandarin-speaking children's acquisition of three subtypes of 2-level recursive sequences exemplified with the so-called "recursive relative clauses (RCs)", reanalyzed as the 2-level tail-, nested-, and mixed-recursion RC sequences. 249 Mandarin-speaking children aged 4–9 years and 46 adult controls are recruited to finish a most-structured elicited Production task. The main findings are as follows: in general, children have acquired 1-level recursive RC sequences by the age of 4, but they have not acquired 2-level tail-recursion RC sequences until the age of 6, they have not acquired 2-level mixed-recursion RC sequences until the age of 8–9, and they have not acquired 2-level nested-recursion RC sequences until the age of at least 10; before acquiring 2-level recursive RC sequences, children tend to replace them with 1-level recursive RC sequences or coordinate structures. This experimental study provides new data and accounts for the development of the faculty of linguistic recursion, and also evidence in support of the formal definition/classification system for recursion. Further, this study makes more elaborate by subdivision the part of Chomsky Hierarchy (1959) claimed to be unique to natural language. [ABSTRACT FROM AUTHOR]