聲調相似度對漢語周歲嬰兒聲調知覺的影響

The Effect of Acoustical Similarity on Lexical- Tone Perception of One- Year-Old Mandarin- Learning Infants

在周歲左右，嬰兒的語音知覺能力經歷快速的變化。嬰兒開始呈現語言特定的知覺處理歷程，例如，開始降低對外語的語音音段（例如，元音與輔音）敏感度，同時提高對母語語音及超音段（例如，音韻規律）的知覺敏感度。然而，到目前為止，只有少數的研究探討「聲調」，這個在聲調語言當中用來區分音節語義的重要語音單位。而且，尚無研究探索漢語為母語嬰兒的聲調知覺發展。本研究的目的在於探究嬰兒對母語聲調知覺的發展，特定而言，檢視聲調之間聲學特性相似的程度，是否會影響嬰兒對不同聲調對比區辨的敏感度。周歲大的嬰兒（n = 109），參加以「轉頭步驟（head-turn procedure）」進行的聲調區辨實驗。其中一組分辨聲學特性差異最大的「一聲和三聲（n = 33）」，另一組分辨聲學特性最接近的「二聲和三聲（n = 36）」，還有一組區分聲學特性相似性在兩組對比之間的「二聲和四聲（n = 40）」。結果顯示，一聲和三聲對比的區辨正確率（M = 73.39%），明顯地高於二聲和三聲（M = 60.74%）及二聲和四聲（M = 57.87%）的區辨正確率。此外，結果也顯示當嬰兒區辨一聲及三聲時，目標音節為「三聲」會比「一聲」的區辨正確率高，也就是呈現「方向不對稱性」。但是此一現象只出現於聲學特性差異最大的一及三聲對比，其他聲調對比沒有此一現象。研究結果呈現周歲嬰兒的漢語聲調知覺發展情形。而聲調的聲學相似性對區辨敏感度的作用，也意涵一般聽覺發展機制在嬰兒發展母語聲調知覺上的重要性，以及周歲嬰兒對聲調聲學線索的處理特性與說漢語的大人不同。

Speech perception abilities undergo rapid changes around the first birthday, such as developing the language- specific phonetic perception and word segmentation, but only a few studies have examined the development of lexical-tones, an essential phonetic unit to distinguish the meanings of syllables in Mandarin Chinese. This study explored the native tone perception of one- year-old Mandarin- learning infants. Specifically, this study addressed whether the acoustic similarity between lexical tones affected infants' perceptual discrimination performance. Infants (n = 109) were tested with the conditioned head- turn procedure when discriminating tone contrasts, Tone 1 vs. 3, 2 vs. 3, and 2 vs. 4, varying in the similarity of average fundamental frequency (F0) and F0 contour. Results showed that infants better discriminated tone contrast with greater acoustical differences (Tone 1 vs. 3), but they were less accurate discriminating acoustically similar tone contrasts (Tone 2 vs. 3 and Tone 2 vs. 4). Directional asymmetry was evident with the Tone 1 vs. 3 contrast, as the change from the background Tone 1 syllable to the target Tone 3 syllable was easier than the reverse. The results suggest that auditory processing is the essential mechanism for one- year- old infants to perceive native lexical tones, and that the perceptual mechanism for lexical tone in infants differs from Mandarin- speaking adults.