Forty Years of Development of Study on Incidental Vocabulary Acquisition in the Field of Second Language Acquisition: From 1984 to 2014

词汇知识对语言能力至关重要。附带词汇习得作为词汇学习方法的一种，因其具有的普遍性、语境相关性、个体性而广受二语习得研究者的关注。本文基于既有文献，并借助Citespace软件，从指导理论、变化趋势、现有不足三个方面，对过去四十年间二语习得领域内附带词汇习得相关的研究进行了回顾。在指导理论方面，本文简要介绍了在相关研究中起到重要影响的三个理论，即输入假说、投入量假说和双重编码理论；在变化趋势方面，本文总结出过去四十年间，相关研究的主要三个变化趋势，即研究重点从发生条件向学习者个体的认知过程的转变、输入模式从单一的阅读材料输入向多模态输入的转变、词汇测试方法从传统的客观纸笔测试向主观测试方法、计算机辅助测试方法的转变。基于这些内容，在现有不足方面，本文讨论了未来的研究应该更加关注的五个方面：1) 目标习得词汇本身固有的特征。现有研究过度关注词汇学习的外部因素，而忽视了目标习得词汇本身的发音、形式、类型等特征可能对附带词汇习得结果造成的影响。目前已有研究证实词汇的类型能显著影响附带词汇习得效果，因此，后续研究可以讨论词汇的其他内在特征，如拼写方式等对附带词汇习得效率的影响。2) 能够影响附带词汇习得效果的因素的影响能力。不同因素对二语学习者附带词汇习得和留存的影响能力的差异可以为教材的编写提供依据，如教材编写是否需要提高关键词复现频率、注意确保语境信息充分性等。此外，同一因素对不同母语背景的二语学习者的附带词汇习得效果的影响也可能存在。3) 目标二语不同、语言背景不同的二语学习者群体。当前研究的研究对象主要集中于英语二语学习者，而对其他语种的二语学习者的研究则存在空白。更值得注意的是，语言少数群体与移民群体在附带词汇习得研究中长期被忽视。相较于普通二语学习者，语言少数群体和移民群体的语言学习动机与语言学习环境与一般的二语学习者存在较大差异，可能表现出独特的语言行为特征，是值得重点关注的特殊二语群体。4) 对多词词项的习得。现有的附带词汇习得研究多聚焦于对单个单词的学习，但在自然语境中，母语者对多词词项的使用频率很高，而二语学习者对多词表达的掌握却相对薄弱。二语教师与研究者应加强对多词词项及与其相关的搭配的关注。5) 词汇知识测试相关的理论和方法。词汇知识是多维度的，远非形–义联结所能涵盖。目前，由于缺乏统一理论框架，二语研究者采用的词汇测试方法往往精确性不足，普遍忽视对学习者在搭配、内涵意义、及语体意义等实用维度上的词汇知识的考察，导致研究结论难以准确反映不同因素对各维度词汇知识的影响的差异。未来实验设计应立足词汇知识的多维本质，构建更精准的词汇测试体系。Vocabulary knowledge is crucial for language proficiency. As an universal, contextualized and individualized way to learn lexical items, incidental vocabulary acquisition has attracted considerable academic attention for nearly four decades. Based on the previous literature and the help of Citespace, this literature review aims to provide an overview of previous research on incidental vocabulary learning in the field of second language acquisition by focusing on three main aspects: the guiding theoretical frameworks, the changing trends and the current shortcomings. For the guiding theories, this study briefly introduces three hypotheses that are related to the experiments in this academic field, namely, Input Hypothesis, Involvement Load Hypothesis and Dual Code Theory. As for changing trends, the findings identify some changes in researchers’ focus, types of input and methods used to test learners’ vocabulary knowledge. Based on this, further research in this area calls for attention to five aspects as follows: 1) The characteristics of target vocabulary itself. Current researchers focus on external factors of vocabulary learning while neglecting the potential influence of the pronunciation, morphology and types of target words on learners’ learning outcomes. Since some experiments have preliminarily concluded that the type of vocabulary can affect the vocabulary retention, other characteristics of vocabulary that have not been discussed yet should also be noted in the future research. 2) The predictive power of factors that can affect the effectiveness and retention of incidental vocabulary learning for second language learners. The importance of different factors can serve as a reference for experts in designing teaching materials, such as increasing the frequency of the occurrence of key words and ensuring that contextual information is rich enough. Additionally, the degree to which the same factor can predict the learning effects may differ among learners of different second languages. 3) Second language learners of different language backgrounds. Present researches primarily focus on second language learners of English, leaving learners of other languages undiscussed. Moreover, linguistic minorities and immigrants are ignored in most of the research on incidental vocabulary learning. Compared with other L2 learners, they may differ in their motivation and approaches to learn the target language and hence display different language performance in the experiment. In another word, they are the special group of L2 learners who are worth more attention. 4) The acquisition of multiword expressions. When it comes to incidental vocabulary learning, we usually mean the incidental learning of isolated words. However, considering the high frequency of use of multiword lexical items in natural language environment and second language learners’ relatively weak mastery of collocations and idiomatic expressions, multiword items and collocations should receive more attention from teachers and researchers. 5) Vocabulary knowledge test theory and methods. Word knowledge is multidimensional and is far beyond the knowledge of form and meaning. Currently, due to the lack of a unified theory, the methods used by second language researchers to test learners’ vocabulary knowledge are often not precise enough. They often neglect learners’ mastery of word collocations, connotative meanings and stylistic meanings, to name but few, which are important for practical word use. This may result in research findings that do not accurately reflect the influence of different factors on learners’ vocabulary knowledge in different aspects. Therefore, future experiment designers should take the multidimensional nature of vocabulary knowledge into consideration and make efforts to test learners’ knowledge more accurately.