Intonational Structure Influences Perception of Contrastive Vowel Length: The Case of Phrase-Final Lengthening in Tokyo Japanese.

Recent research has proposed that listeners use prosodic information to guide their processing of phonemic contrasts. Given that prosodic organization of the speech signal systematically modulates durational patterns (e.g., accentual lengthening and phrase-final (PF) lengthening), listeners' perception of durational contrasts has been argued to be influenced by prosodic factors. For example, given that sounds are generally lengthened preceding a prosodic boundary, listeners may adjust their perception of durational cues accordingly, effectively compensating for prosodically-driven temporal patterns. In the present study we present two experiments designed to test the importance of pitch-based cues to prosodic structure for listeners' perception of contrastive vowel length (CVL) in Tokyo Japanese along these lines. We tested if, when a target sound is cued as being PF, listeners compensatorily adjust categorization of vowel duration, in accordance with PF lengthening. Both experiments were a two-alternative forced choice task in which listeners categorized a vowel duration continuum as a phonemically short or long vowel. We manipulated only pitch surrounding the target sound in a carrier phrase to cue it as intonational phrase final, or accentual phrase medial. In Experiment 1 we tested perception of an accented target word, and in Experiment 2 we tested perception of an unaccented target word. In both experiments, we found that contextual changes in pitch influenced listeners' perception of CVL, in accordance with their function as signaling intonational structure. Results therefore suggest that listeners use tonal information to compute prosodic structure and bring this to bear on their perception of durational contrasts in speech.