Recent work has used artificial language experiments to argue that hierarchical representations drive learners' expectations about word order in complex noun phrases like these two green cars (Culbertson & Adger 2014; Martin, Ratitamkul, et al. 2019). When trained on a novel language in which individual modifiers come after the Noun, English speakers overwhelmingly assume that multiple nominal modifiers should be ordered such that Adjectives come closest to the Noun, then Numerals, then Demonstratives (i.e., N-Adj-Num-Dem or some subset thereof). This order transparently reflects a constituent structure in which Adjectives combine with Nouns to the exclusion of Numerals and Demonstratives, and Numerals combine with Noun+Adjective units to the exclusion of Demonstratives. This structure has also been claimed to derive frequency asymmetries in complex noun phrase order across languages (e.g., Cinque 2005). However, we show that features of the methodology used in these experiments potentially encourage participants to use a particular metalinguistic strategy that could yield this outcome without implicating constituency structure. Here, we use a more naturalistic artificial language learning task to investigate whether the preference for hierarchy-respecting orders is still found when participants do not use this strategy. We find that the preference still holds, and, moreover, as Culbertson & Adger (2014) speculate, that its strength reflects structural distance between modifiers. It is strongest when ordering Adjectives relative to Demonstratives, and weaker when ordering Numerals relative to Adjectives or Demonstratives relative to Numerals. Our results provide the strongest evidence yet for the psychological influence of hierarchical structure on word order preferences during learning.

There are certain recurrent features of language that characterise the way whole language systems are structured, and others that target specific categories of items within those wider systems. For example, languages tend to exhibit harmonic (i.e. consistent) ordering between heads and dependents, making it a kind of system-wide regularity. While this tendency is generally robust, some categories of linguistic items deviate from this trend. We examine one such case of non-harmony, namely the order of the noun with respect to two dependents -- adjectives and genitives. Using two silent gesture experiments, this study tests the hypothesis that category-specific cognitive biases favour postnominal adjective order and prenominal genitive order. Further, we show that the influence of these biases is revealed in contexts where no conventionalised system is in place. When a system is in place, participants learn that system, and category-specific biases do not impact their learning. Our results suggest that different types of linguistic contexts reveal the influence of separate types of cognitive biases, such that some are active during learning and others are active during language creation.