Evidence for word order harmony between abstract categories in silent gesture

Cross-category harmony is the tendency for languages to use consistent orders of heads and dependents across different types of phrases. For example, languages tend to either place both verbs and adpositions before their dependents (e.g., 'seethe girl', 'tothe store' as in English) or after (e.g., 'the girlsee', 'the storeto' as in Turkish). Harmony has been argued to reflect a cognitive bias for simpler rules: a single high level abstract rule is simpler to learn than multiple rules, one for each type of head and dependent (Culbertson and Kirby, 2016). This has been supported by recent experimental work indicating that learners prefer to consistently order nouns either before or after different nominal modifiers (e.g. Culbertson et al., 2012, 2020a) and different types of verbs (Motamedi et al., 2022), and generalise the relative order of verb and noun to the order of an adposition and noun (Wang et al., in press). However, these studies all use the exact same set of nouns for both the training and testing stimuli. This leaves open the possibility that participants are noticing surface-level patterns, i.e., matching the position of specific nouns across phrases. This would give the appearance of a preference for cross-category harmony, but would not reflect anything about the alignment of categories, or a preference for fewer abstract rules. This paper describes three experiments that were designed to establish whether there is a cognitive bias for cross-category harmony between the adpositional phrase and the verb phrase which persists when the possibility of using surface-level patterns is removed.