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* Corresponding author. Dr Jamie Lingwood, School of Languages, Cultures and Societies, University of Leeds, LS2 9JT, UK. E-mail: [email protected]
Introduction
Knowledge of adjectives is a central component in understanding and producing language. Adjectives are a critically important grammatical class for expanding children's repertoire beyond naming to describing, modifying, and discriminating entities. They can help children predict upcoming nouns in the speech stream (Tribushinina & Mak, 2016) and extend vocabulary. However, they have a protracted developmental course in both comprehension and production (Berman, 1988; Ninio, 1988; Ramscar, Thorpe, & Denny, 2007; Waxman & Booth, 2001). Although 30-month-olds typically have around 50 adjectives in their repertoire (Dale & Fenson, 1996), children are unable to use adjectives flexibly until around four years of age, e.g., by being unable to extend novel adjectives (e.g., blickish) to the properties of a new object (Klibanoff & Waxman, 2000), a late stage compared to the acquisition of other open word classes (Caselli et al., 1995; Gentner & Boroditsky, 2001; Ninio, 1988; Salerni, Assanelli, D'Odorico, & Rossi, 2007; see Gasser & Smith, 1998, for a review). Several explanations for this late emergence have been proposed. These relate to the relatively low frequency of adjectives in the input – estimated at around 10% of tokens by English-speaking caregivers (Sandhofer, Smith, & Luo, 2000; see also Behrens, 2006; Salerni et al., 2007; Tribushinina & Gillis, 2012; Tribushinina et al., 2014) – as well as to challenging features of the adjectives themselves; specifically, their semantic, syntactic, and pragmatic variability (Fernald, Thorpe, & Marchman, 2010; Ricks & Alt, 2016; Thorpe & Fernald, 2006; Tribushinina et al., 2014).
To develop models of adjective acquisition, we need a comprehensive survey of the quantity and quality of adjectives that children experience in the input. Here we measure three- and four-year-olds’ quantitative and qualitative exposure to adjectives across a range of interactive and socioeconomic contexts. We analyse patterns of adjective use in three sources of child-directed speech (CDS) in order to: (i) measure the variability in adjective use across interactive and socioeconomic contexts; and (ii) reflect on how features of the input might help (or hinder) adjective acquisition. Despite the clear importance and relatively late mastery of adjectives in children's repertoires, adjectives have traditionally received...