不同言語速度下國語韻律的計時等時性

The Timing Isochrony of Spoken Mandarin at Different Speaking Rates

本研究的主要目的在了解國語說話者在語音製造和知覺的韻律計時特性，考驗國語以音節計時的假設。實驗一使用的語音材料包括三十三個片語句組及兩篇短文，有三十位正常的說話者（男女各半）參與錄音實驗。由於言語中時長變項易受到語速影響，為控制語速在實驗一中先使用節拍器調節說話者的語速，再讓說者以同樣的速度說出語句。共有五種語速變化。以頻譜圖分析各說話者在各句中各音段的時長（子音、母音、停頓等）。使用成對變異指數（pairwise variability index, PVI）比較語句中兩種假設性等時單位（全音節單位、母音起始單位）的時長變異性。結果發現母音起始單位的PVI顯著小於以全音節為計時單位的PVI，顯示母音起始單位較具有等時性。以母音為計時單位起點正是所謂的語音知覺中心（perceptual center, P-center）的所在。實驗二使用較自然的語速控制方式，說者先聽語速示範帶後再說出句子。有二十一位正常的說話者（男女各半）參與錄音，並分析各語句音段時長後，同樣地以PVI考驗兩種計時單位的等時性，結果和實驗一相近似。實驗一和實驗二的結果顯示不管使用何種語速控制方式母音起始單位皆顯著地比全音節單位較具有等時性。在實驗三中有十八位受試者評估具有不同PVI句子的自然度，結果發現自然度分數和PVI值呈現高負相關，即PVI值愈大聽起來愈不自然，並發現使用母音起始單位計算的PVI值和自然度分數間的相關高於使用全音節單位PVI和自然度間的相關。無論是在言語的製造和知覺方面，本研究的結果支持母音起始單位為國語韻律計時的等時單位。

The behavior of speech timing plays an important role in the process of speech perception and production. The source of speech rhythm is based on the "isochrony". Isochrony unit is a hypothetical unit which has an equal duration interval existing in the speech stream. The users of a language base on the isochrony unit to process the speech information during speech process. The purpose of this study is to investigate two candidates of speech timing units in connected Mandarin. The first candidate is "the whole syllables unit (pause / gap + CV)" and the other is "the rime onset unit (rime + pause / gap + C)". This study consists of three experiments; the first two experiments are production tasks, and the third is a perceptual task. In the first experiment, 30 mandarin speakers read 33 sets of Chinese phrases and sentences and two passages at five speaking rates by using a metronome to modulate the speaking rates. Segmental durations were obtained via acoustic analysis, and then, the pairwise variation index (PVI) was computed for the two candidate units to compare the degree of isochrony. The results show that the rime onset unit had significantly less PVI value than the whole syllable unit, and the two kinds of units had the maximum difference at the slow speaking rates, but at the fast speaking rates there was no difference between them. The second experiment is the replicate of the first one, and the major difference is the method of speaking rate control. The second experiment had similar results as the first one, again, the rime onset unit had the less PVI. In the third experiment, 18 listeners estimated the degree of naturalness of 24 sentences with different PVI values. The results show that the degree of naturalness is highly correlated with PVI values; moreover, for the PVI calculated by the rime onset unit, the correlation is stronger than that by whole syllable unit. These findings support the rime onset unit is the isochrony unit in speech timing process of Mandarin. The results suggest the basic unit of Mandarin speech timing is related with rime onset, where is also known as the locus of "perceptual center".