Storage and computation in syntax: Evidence from relative clause priming

In morphology, researchers have provided compelling evidence for the storage of even fully compositional structures that could otherwise be computed by rule. For example, a high-frequency word composed of multiple morphemes (e.g., root + plural inflection) may be stored directly rather than computed on the fly (e.g., Baayen, Dijkstra, & Schreuder, 1997). Here, we investigate similar questions of storage and computation in syntax, a domain in which evidence of storage of fully compositional structures has been less forthcoming. We approach this question using syntactic priming, a method exploiting the tendency of individuals to repeat syntactic structures that they have recently produced (Bock, 1986). As a test case, we investigate relative clauses (RCs). RCs are both abstract and syntactically complex but are nevertheless frequent in natural language (Roland, Dick, & Elman, 2007). Moreover, differences in processing complexity between different RC types are at least partially predicted by frequency (e.g., Reali & Christiansen, 2007). RCs are therefore an ideal domain to look for evidence of storage of abstract, compositional syntactic structure. If the structures underlying high-frequency RC types are stored and retrieved from memory as whole units instead of being computed online from smaller units, then these stored structures should be susceptible to priming. Across three experiments, we observed that priming of object-extracted RCs is sensitive to a) the type of noun phrase in the embedded subject position (a full NP vs. a pronoun), and b) the type of relative pronoun (who vs. that). These results suggest that the representations of some types of RCs involve storage of large units which include both syntactic and lexical information. We interpret these results as providing support for models of syntax that allow for complex mixtures of storage and computation.