Role of word-external contexts in native speakers' identification of vowel length in Japanese.

Five groups of native Japanese listeners were assigned to five conditions differing in word-external contexts. In the Intact condition, three types of target disyllables, /mVmV/, /mV:mV/, and /mVmV:/ were spoken in a carrier sentence at two speaking rates. In the other four conditions, the target disyllables of the Intact condition were excised from the original carrier sentence (Excised); embedded in the carrier sentence of the other rate (Mismatch); presented only with the preceding three syllables (Preceding), and presented only with the following three syllables (Following). The accuracy for identifying the word types was higher for the Intact than Excised and Mismatch conditions, indicating that the presence of the carrier sentence with an appropriate rate was important for accurate identification. It was also found that either the preceding or the following short phrase contained sufficient information for identifying the word types. Further, there were effects of the preceding and following phrases on both the first and second vowels of the targets, suggesting that the distant speech materials more than two phonemes away from a target in both sides can affect identification accuracy. Implications are discussed in terms of the adjacency principle for rate normalization.