特定型語言障礙學齡兒童的語音知覺特性

Abstract

特定型語言障礙兒童（specific language impairment, SLI）的非語文認知及生理各方面發展正常，語言學習卻特別出現困難。有些以英語語障兒童為對象的研究認為特定型語言障礙兒童有「快速聽覺處理缺陷」，故使其語言發展受阻，亦即，相較於年齡對照組，特定型語言障礙兒童不易利用短促且快速變化的聲學線索來區辨語音的差異。本研究的目的之一，即在於檢驗國語特定型語言障礙學齡兒童是否出現和英語語障兒童相似的缺陷。此外，本研究也檢驗國語語障兒童是否出現國語「聲調」的處理困難。本研究以系列的三個實驗來檢視特定型語言障礙學齡兒童的語音知覺特性。實驗一以正常的大學生為受試者，發現輔音共振峰頻率變化速率會影響輔音區辨的敏感度，「時間」效果也同樣出現在區辨非語音的「連續音頻（tone sweep）」。實驗二以語言正常發展的六歲幼兒為受試者，發現「時間」並沒有顯著影響幼兒區辨輔音「構音部位」及「連續音頻」，而「基頻範圍」也對「聲調」區辨沒有顯著影響。迴歸分析的結果顯示，幼兒「聲調」敏感度最能解釋整體語音區辨敏感度的變異量。實驗三以國語為母語的語障兒童（平均年齡九歲，n = 14）以及年齡和非語文認知能力相當的對照組兒童（n = 17）為受試者，實驗作業為語音（塞音構音部位及國語聲調）及非語音（連續音頻, tone sweep）的區辨作業。結果顯示，和對照組相比，語障兒童對「聲調」及輔音「構音部位」的區辨正確率表現較差，但是對「連續音頻」的區辨敏感度則與對照組沒有顯著差異，顯示語障兒童有語音特定的知覺處理缺陷。延長語音聲學特徵並未提升語障兒童的區辨正確率，在輔音的共振峰轉接（formant transition）時間較長時，語障兒童的「構音部位」聽辨表現依然比對照組兒童差，顯示其處理時間較長的聲學線索也有困難。因此，語障兒童的處理缺陷並非都來自處理短促訊息的「時間」限制；而是對需要整合「較長」時間聲學特性的輔音共振峰轉接以區辨「輔音」，及一段時間「基頻（fundamental frequency）」變化來區辨「聲調」出現困難。整體而言，學齡語障兒童出現「語音」處理限制，但是這樣的限制似乎不是「聽覺」處理的限制，而是語音知覺表徵形成或運作的困難。此外，「聲調」基頻範圍擴大時，有助於提升區辨正確率，同時，「聲調」敏感度也對國語兒童語音知覺能力、口語理解能力有重要影響。既然「聲調」是國語的特性，這樣的結果也顯現特定型語言障礙兒童「語言特定（language specific）」的語音處理困難。

Children with specific language impairment (SLI) are characterized by difficulty with language learning but without severe cognitive and physical development deficits. Some studies on English-learning SLI children propose that these children are restricted by “rapid temporal processing deficit”, so that they can’t efficiently process speech sounds, and result in language learning difficulties. The study aimed to investigate the “rapid processing deficit” hypothesis in Mandarin-learning SLI children, and also examined the consonant and lexical tone perception in this group of children. A series of three experiments were conducted. Experiment 1 explored the “temporal effect” on Mandarin-speaking adults discriminating stop consonants with different place of articulation, and found that the duration of formant transition affected the consonant discrimination performance. Experiment 2 investigated the “consonant” and “lexical tone” perception in 6-year-old typically-developed children, and failed to found the “temporal effect” on consonant and “tone sweep” discrimination. However, the regression analysis showed that “lexical tone” contributed more in accounting for the overall phonetic discrimination variance. Experiment 3 compared the Mandarin-learning 9-year-old SLI children (n = 14) with age and nonverbal IQ matched control group (n = 17) on three speech discrimination tasks -- “lexical tone”, “consonant, the place of articulation (stop-vowel syllables)”, and “tone sweep”. The results showed that SLI children performed significantly less accurate in “lexical tone” and ”consonant” discrimination than controls, but they performed similar “tone sweep” sensitivity with controls. It seemed the perceptual processing deficit of SLI was “speech-specific” rather than “auditory” in detecting spectral cues of lexical tones and temporal cues of stop-vowel syllables. On the other hand, the speech processing deficit might not be “rapid processing limit”. Results showed that lengthening the formant transition didn’t improve the consonant discrimination performance. The performance of SLI children was still poorer than controls on discriminating consonants with prolonged formant transitions. Thus, Mandarin-learning SLI children might have processing difficulties in integrating essential acoustic-phonetic cues to detect phonetic differences. Besides, exaggerated F0 range of lexical tones improved both groups’ performance. Results of regression analysis showed that lexical tone sensitivity contributed most in accounting for the overall speech discrimination variance, and also significantly related to language production performance. Results suggest that lexical tone processing is critical to Mandarin-speaking SLI children to learn language and also demonstrate the “language-specific processing deficit” in SLI children.