台灣大學生在兩種自然口語類型相異詞比例及詞彙密度之比較研究

A Comparative Study on Lexical Richness and Lexical Density in Two Spontaneous Speeches of Chinese EFL Learners

Vocabulary is essential for language acquisition and language use with regard to the use of content words and function words as part of the linguistic competence. Lexical density has been considered a valid measure to determine the relationship between lexical items and grammatical items in any written or spoken texts. Results of previous studies revealed that task types can be a variable affecting lexical density (Lauren, 2002). On the other hand, since lexical variation and lexical density are crucial in detecting the literacy degree of a spoken text and semi-direct oral proficiency interview (SOPI) has been recognized as an efficient medium to measure ESL/EFL learners' spoken performance (Shohamy, 1994; Wu, 2005), this study thus aims to examine the lexical richness and lexical density of spoken texts obtained from a structured spontaneous speech and a less structured spontaneous speech in two SOPI tests. Speech samples of 51 Chinese EFL college students were collected, transcribed, and analyzed to explore the lexical variation and lexical density of their speech production, with speech samples from six native speakers of English serving as a baseline for comparison. The EFL subjects were further categorized into two proficiency groups on the basis of their scores on the SPEAK test. Results of two major types of lexical variation and lexical density measurements were reported: type-token ratios and lexical density (O'Laughlin, 2001). The results indicated that weighted lexical density is a more reliable measure of a learner's oral vocabulary use.實詞與功能詞的使用是語言能力的一部分，因此字彙在語言習得與語言使用上更顯重要。欲測量文章中實詞與功能詞的關係時，詞彙密度是項具有效度的測量方式（Halliday，1985；Ure，1971）。另外，文獻也顯示測試任務類型會影響詞彙密度（Lauren，2002）。相異詞比例與詞彙密度常用於衡量口語能力，且口語能力模擬測試也被視為可以用來測量以英語為第二外語學生的口語能力的測驗方式。因此，本研究旨在比較台灣大學生在單張圖片及連環圖片兩種自然口語類型測驗中的相異詞比例及詞彙密度。本研究收集51位台灣大學生的口語語料，分析語料中的相異詞比例及詞彙密度。此外，也收集6位以英語為母語人士的語料，以便和台灣大學生的口語表現做比較。再者，本研究根據托福口語測驗成績，將台灣大學生分為高口語能力組與低口語能力組。研究結果顯示低能力組學生在兩種口語測驗中的相異詞比例明顯比以英語為母語人士大，但高能力組的表現卻與以英語為母語人士極為類似。相對地，低能力組在連環圖片的總詞彙密度卻明顯較以英語為母語人士和高能力組低；而低能力組和高能力組在單張圖片的總詞彙密度卻明顯都較以英語為母語人士低。就加權詞彙密度而言，高能力組在連環圖片的詞彙密度明顯較低能力組高；在單張圖片測驗中，低能力組和高能力組的加權詞彙密度卻明顯都較以英語為母語英語人士低。研究結果顯示，加權詞彙密度在測量口語字彙能力時較其他兩種測量方法有效。