In the old days of language acquisition, vocabulary teaching and learning were given little importance (Alemi and Tayebi 2011). However, the scenario today is drastically different as very few language instructors ' if any ' would even consider overlooking the lexical dimension in their regular teaching.
The crucial role of lexis in both first and second language acquisition has been acknowledged by researchers. As Singleton (1999) aptly put it ' 'the major challenge of learning and using a language, whether as L1 or L2, lies not in the area of broad syntactic principles but in the 'nitty-gritty' of the lexicon'. A large body of empirical research has suggested that lexis is a major concern for learners and teachers in the language classroom context. A wide recognition of the crucial role of lexis in language learning and teaching culminated in sets of principles proposed by some vocabulary researchers (Barcroft 2002; Laufer 2005a; Meara 2005; Nation 2005a; S??kmen 1997; Zimmerman 2008).
In fact, language learners themselves regard vocabulary knowledge to be of primary importance and often feel that many of their difficulties in both receptive and productive language use result from inadequate vocabulary (Nation 1990). The crucial role that vocabulary plays in language competence has been repeatedly acknowledged, particularly so since the 1990s. Laufer (1998) stated that the most striking difference between foreign learners and native speakers is in the quantity of words each group possesses. In the same vein, Lewis (2000) argued that the single most important task facing language learners is acquiring a sufficiently large vocabulary.
Apart from their role in the dissemination of scholarly knowledge, academic reading has been found to be sources of vocabulary acquisition for second language (L2) learners (Parry 1991; Vidal 2003). This is especially relevant for students entering English-medium institutions who need to enhance the breadth and depth of their vocabulary knowledge in order to succeed in their academic and professional pursuits.
With regards to the general discussions in L2 acquisition research, one glaring issue has always been whether explicit attention to vocabulary is absolutely necessary in vocabulary learning (Hunt and Beglar 2005; Laufer 2005; Hulstijn 2001).Various studies have come up with opposing conclusions and the consensus appears to be a compromise between the implicit and the explicit, summarized fittingly by Nation (2005) in his assertion that every course should involve some deliberate attention to vocabulary. One important way to develop vocabulary knowledge is through extensive reading. Students by reading extensively will be exposed to different new scope of vocabulary which is necessary in reading comprehension. Extensive reading (ER) is an important aspect of any English as a foreign/second language reading program. Bell (2001) states that ER is a type of reading instruction program that has been used in ESL or EFL settings, as an effective means of developing reading fluency, comprehension, and vocabulary development.
Day and Bamford (2004) argue strongly for including extensive reading in the L2/FL curriculum. There is new piece of evidence that extensive reading can have a significant impact on learners' L2/FL development. Not only can extensive reading improve reading ability, it can also enhance learners' overall language proficiency (e.g., spelling, grammar, vocabulary, and writing). In addition, extensive reading within language is in line with current principles for second and foreign language pedagogy.
1.2. Significance of the study
In line with the points mentioned in the introduction, it is obvious that vocabulary is the key factor in comprehending the texts and researchers believe that there is a language threshold for reading comprehension, that is, students should know 95-98% of the words in a passage so that they could manage deciphering the meaning of the text. The main motivation for the current study aroused from the evidence that although vocabulary has attracted increased interest since the 1980s, researchers and teachers continue to give less importance to it than to syntax and phonology (Laufer 1986, cited in Zimmerman 1997). It is not surprising that vocabulary is a serious obstacle to many L2 learners. In Meara's (1989) study of L2 university students, for example, lexical errors outnumbered grammatical errors.
The picture does not seem to be different in the EFL classrooms in Iran where the focus of vocabulary teaching in most L2 classrooms is highly based on traditional definition-based vocabulary teaching (Zafarani 2009). The students just memorize the vocabulary to pass the exam. Observing these missing points teachers have become aware of the severe problems concerning vocabulary learning.
Researchers have conducted a number of investigations on variables affecting vocabulary acquisition (Nation 2001; Read 2000). Among these, implicit and explicit lexical elaborations have attracted researchers' attention. These are two of the methods used to teach vocabulary. Regarding the significance of the two proposed methods of lexical elaborations and their effects on vocabulary acquisition, in the present study, the researcher intends to concentrate on these methods to show that which one of them affects more on vocabulary acquisition.
1.3. Statement of the problem
In the 1970s, Richards (1976:88) pointed out that 'vocabulary has for some time been one area of the syllabus where the link between approach, method and technique has been neglected. Meara (1980) also lamented the neglect of vocabulary and the treatment of lexis as a 'step child (i.e. secondary consideration) in the field of English language teaching. In recent years, however, there has been a renewed interest in lexis across the world. Broady (2008: 259) contended that vocabulary is no longer 'a Cinderella topic', given its widespread coverage in research journals and major concern in language pedagogy. In a recent editorial about trends in language teaching research, Ellis (2012: 141) referred to Stapleton's (2013) analysis which indicates that vocabulary has received increasing attention. As an important curricular area in language pedagogy, lexis has emerged an issue in research on teacher language awareness (Andrews and McNeill 2005), form-focused instruction (Basturkmen, Loewen and Ellis 2004), and classroom interaction (Dobinson 2001).
Psychological studies about implicit/explicit learning in language acquisition have typically been concerned with the acquisition of grammatical structures. Reber (1967) was the first researcher to formulate a theory of implicit learning on the basis of experiments on the learning of miniature artificial grammars, in which he demonstrated that information was abstracted out of the environment without conscious operations; since then, the analysis of implicit and explicit learning has developed considerably, and theories have been proposed which go beyond the context of learning artificial languages in experimental settings (cf. Ellis 1994b). In the field of vocabulary acquisition, the nature of the implicit/explicit distinction is somewhat different than in grammar learning, and research in this area is still very scarce. Furthermore, it seems that the debate about implicit/explicit learning and vocabulary acquisition has frequently been blurred by a confusion of the issue under discussion. This can be illustrated some extent by the diverse terminology used, contrasting e.g. 'implicit' acquisition vs. 'explicit' directed learning. Therefore, in this research the researcher sought to investigate the effect of explicit and implicit lexical elaboration on Iranian EFL learners' vocabulary acquisition from extensive reading.
1.4. Research Question
Since this study concentrates on investigating the effect of explicit/implicit lexical elaboration on Iranian EFL learners' vocabulary acquisition from extensive reading, the researcher has tried to answer the following question:
1) Is there any significant difference between the effect of explicit and implicit lexical elaboration on Iranian EFL learners' vocabulary acquisition from extensive reading?
1.5. Research Hypothesis
In line with the previous research question a null hypothesis was proposed to be investigated in the study:
There is no significant difference between the effect of explicit and implicit lexical elaboration on Iranian EFL learners' vocabulary acquisition from extensive reading.
1.6. Definition of the Key Terms
Implicit learning: Implicit learning is typically defined as 'acquisition of knowledge about the underlying structure of a complex stimulus environment by a process which takes place naturally, simply and without conscious operation'. (Ellis 1994b: 1).
Implicit vocabulary learning, also known as incidental vocabulary learning, occurs when the mind is concentrated elsewhere, such as on comprehending a written text or understanding spoken material. One of the premises of implicit vocabulary learning is that new words should not be presented in isolation and should not be learnt by mere rote memorization. It follows that new vocabulary items should be presented in contexts rich enough to provide clues to meaning and that learners should be given multiple exposure to items they are supposed to learn (Nation 1990).
Explicit learning: Explicit learning is said to be characterized by 'more conscious operation where the individual makes and tests hypotheses in a search for structure' (Ellis 1994b: 1).
Explicit vocabulary learning, engages learners in activities that focus attention primarily on vocabulary. Several key principles which can help guide teachers in deciding basic questions of what to teach and how to teach include integrating new vocabulary with old, facilitating imaging, using a variety of techniques, providing a number of encounters with a word, encouraging independent learning strategies, and promoting a deep level of processing (Sokmen 1997).
Elaboration: Elaboration (Kim 2006: 344) is the extension of the input the L2 learners are exposed to, by giving the meaning of the words after the words which the L2 learners are unfamiliar with. Elaborative devices (Ellis 1994b, Lee 2007, Watanabe 1997) in this study include definitions and synonyms which come directly after the target words.
Extensive reading: Bell (2001) states that ER is a type of reading instruction program that has been used in ESL or EFL settings, as an effective means of developing reading fluency, comprehension, and vocabulary development. Day and Bamford (2004) argue strongly for including extensive reading in the L2/FL curriculum. There is new piece of evidence that extensive reading can have a significant impact on learners' L2/FL development. Not only can extensive reading improve reading ability, it can also enhance learners' overall language proficiency (e.g., spelling, grammar, vocabulary, and writing). In addition, extensive reading within language is in line with current principles for second and foreign language pedagogy.
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