Effects of prosodic boundaries on ambiguous syntactic clause boundaries in Japanese

We report the results of experiments designed to investigate the effects of prosodic boundaries on resolving ambiguous syntactic clause boundaries in Japanese. The head-final, prodrop nature of this language generates abundant syntactic attachment ambiguity for sentences that contain relative clauses. Two types of sentences with differing head nouns modified by relative clauses were examined. Syntactic attachment preferences for these two types of sentences in the absence of overt prosody were assessed in a written study. Results indicated that readers retrieved one clear meaning for one type whereas ambiguity was not clearly resolved for the other type. A sentence comprehension study was conducted using auditory versions of both sentence types, each produced with two prosodic structures. Results demonstrated the crucial use of prosodic boundary information in retrieving syntactic clause boundary information. Most importantly, prosodic boundaries affected the way listeners posited empty pronouns for the subject of main or subordinate predicates. These results demonstrated the fundamental importance of prosodic phrasal structure to the assignment of syntactic constituency during sentence comprehension, particularly in the case of a headfinal, pro-drop language.