| In recent decades, theories and researches about incidental vocabulary acquisition (IVA) have aroused great and continuous attention from scholars of SLA. A great number of researchers have already done plenty of researches about IVA through reading with wealth of findings. However, much fewer studies have been done about IVA in listening, and most present ones are just applying findings in reading to listening with lack of original researches based on listening itself. Moreover, scarcely any researches have investigated about how to improve effectiveness of IVA through listening, let alone from the perspective of unknown word density. This thesis tries to explore the influence of unknown word density to listening comprehension and IVA by using Rieder’s degree of focus and enrichment theory as theoretical support.Based on 95%-98% text coverage (percentage of running words already known by learners in a text) as the optimal range for reading comprehension and IVA claimed by many researchers (e.g. Laufer,2001; Nation,2006), this study sets up four unknown word densities (the opposite of term text coverage) to investigate the best text coverage for listening comprehension and IVA. Three research questions are thus put forward. (1) In terms of listening comprehension and incidental vocabulary acquisition, are there any differences among the four densities in immediate test? If there is or are, what is/are the difference/differences? (2) Are there any differences about incidental vocabulary acquisition among the four densities in the post test? If there is or are, what is/are the difference/differences? (3) What is the optimal unknown word density for IVA through listening? The aim of this research is trying to find out the optimal unknown word density for IVA through listening and thereby benefit listening teaching and vocabulary learning.40 non-English major college students in the first grade were chosen from a top university from China. They were asked to participate in a vocabulary size test before the experiment to make sure the consistency of subjects. Nonwords were used as target words to make sure they are unknown to all participants. Participants were free to use glossaries containing nonwords and some distracting words during the listening process, but they were not informed about the vocabulary test before listening. After listening, all participants handed in their answer sheets and glossaries, and took the vocabulary test. After the vocabulary test,10 subjects were chosen randomly to take part in a semi-structured interview. And one week later, they had the same vocabulary test as in immediate test to see the retention of words. SPSS 19.0 was used for analyzing data collected. The results show that 1% unknown word density has the highest pickup rate both in immediate and post test while 6% density gets the lowest; pickup rate of 2% density is lower than that of 4% density in immediate test but becomes higher in the post test; there are significant differences about listening comprehension among the four densities with score of 1% density being significantly higher than the other three and 2% getting the lowest. Subjects’ answers in interview also suggest that the two passages of 2% density are the most difficult ones, which is not caused by nonwords.There are several major findings in this research. First, there exists incidental vocabulary acquisition in the listening process. Second, 1%-2% unknown word density is probably the best range for IVA through listening. Third, there is a positive correlation between listing comprehension and immediate vocabulary acquisition. Fourth,1% unknown word density facilitates listening comprehension the best, and the other three densities’ influence to listening comprehension does not have any significant differences. This thesis is supposed to have both theoretical and practical significance for L2 IVA investigation, especially L2 IVA through listening, and the findings also have referential value for listening material design. |
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