- 認知科学 (ISSN:13417924)
- vol.13, no.3, pp.428-442, 2006 (Released:2008-11-13)
In spoken sentence comprehension, prosody is regarded as an important information source for syntax. However, prosody can also be affected by various non-syntactic factors. The present study demonstrates that lexical accent, which itself is not relevant to syntax, is relevant to, and can have a considerable impact on the resolution of syntactic ambiguity in human sentence comprehension. In a (LB) left-vs. (RB) right-branching ambiguity in Japanese as in the example below, the presence or absence of lexical accent (indicated by “’”) on the initial adjective, (e.g., ao’i (blue): accented vs. kiiroi (yellow): unaccented) is known to influence phrasal level prosody. This in turn affected listeners' analyses on branching structure, as will be shown in the production study. ao’i⁄kiiroi siidi’i-no ke’esu-o sa’sitekudasai blue⁄yellow CD-Gen case-Acc point “Point at the case of the blue⁄yellow CD.” (LB-interpretation) “Point at the blue⁄yellow case of the CD.” (RB-interpretation) In the production task, naive speakers (n=7) gave verbal instructions to their partners to identify the target object, using a fixed phrase as indicated in the example above, where either RB or LB was intended. The F0 contour on the collected utterances showed little distinctive difference among conditions except for the LB-intended utterances with an accented adjective. The collected utterances were then fed to a perception test (forced choice task identifying the intended meaning) with a separate group of subjects (N=48). Listeners' performance in correctly identifying LB-intended utterances was significantly better for items with an accented adjective (ao’i) than with an unaccented adjective (kiiroi), whereas performance on RB-intended utterances were relatively poor regardless of the presence of an accent on the initial adjective. The results of the perception study can be explained by what was found in the production study: the successive downstep (which is conditioned to occur following an accented item) as a major cue indicating a left-branching structure was not available for items with an unaccented adjective. It is also suggested that when the relevant F0 cue is not available or useful, hearers rely more on durational cues.