Testing language acquisition models: Null and overt topics in Mandarin

Parameter setting is either precipitous (Gibson & Wexler, 1994) or it is gradual in response to input frequency (Yang, 2002, 2004). In this study, we compare these models against the empirical domain of subject and (direct) object drop in Mandarin. We conducted a corpus-based study of the speech of 47 Mandarin-speaking children aged 1;2-6;5, and their caregivers, from the CHILDES database. The results show that before age 1;8 all the children used null subjects and null objects in a target-like fashion, which reveals that the parameter that governs null topics is set from very early on, even if the presence of disambiguating evidence for [+Null Topic] patterns is low. Besides, children's ba constructions, which require an overt object, reliably included this object from the first occurrence although its frequency was scarce in the input. Our results indicate that the setting of certain parameters occurred early independently of the input.