The importance of vocabulary knowledge

Introduction
CHAPTER 1
INTRODUCTION
1.1 Background and motivation
The aim of the present thesis is to investigate the relationship between EFL learners’ depth and breadth of vocabulary knowledge[1] and the extent to which vocabulary knowledge contributes to listening comprehension in English as a foreign language[2].
Over the last 20 years vocabulary has assumed a more prominent role within the field of second language acquisition research, and vocabulary is no longer “a neglected aspect of language learn­ing” as it was designated by Paul Meara in 1980. While researchers in applied linguistics were pre­viously concerned mainly with the development of learners’ grammatical, and to some extent phono­logical, competence, more attention is now being paid to their lexical competence. This has happened as a consequence of the growing realisation that lexical competence forms an important part of learners’ communicative competence in a foreign language. As observed by McCarthy (1990: viii) in the introduction to his book Vocabulary:
No matter how well the student learns grammar, no matter how successfully the sounds of L2 are mastered, without words to express a wide range of meanings, communication in an L2 just cannot happen in any meaningful way.
The importance of vocabulary knowledge in communicative competence has similarly been stressed by Meara who has argued that “lexical competence is at the heart of communicative competence” (1996a: 35) and that “vocabulary knowledge is heavily implicated in all practical language skills (Meara and Jones, 1988: 80).
In order to fully uncover the role of vocabulary knowledge in second language use, we therefore need to explore the extent to which it contributes to different language skills. The above claims by Meara have been solidly supported by findings from a considerable number of empirical studies investigating the relationship between learners’ vocabulary knowledge and their reading compre­hension. Such studies have found that vocabulary knowledge is a significant determinant of reading success in L1 as well as L2. However, as will be come evident in the present thesis, very little re­search has addressed the relationship between vocabulary knowledge and the skill of listening in L2 and, at present, we can only tentatively assume that vocabulary knowledge will also play some kind of role in learners’ listening comprehension in English as a foreign language. Research of the relationship between vocabulary knowledge and listening is important as findings from studies of reading cannot automatically be applied to listening despite the fact that reading and listening are both receptive skills.
The present study is thus motivated by a critical lack of empirical research on the relationship be­tween vocabulary knowledge and listening comprehension and by the resultant need to explore the extent to which learners’ vocabulary knowledge will contribute to their listening success in L2.
A prerequisite for exploring the relationship between vocabulary knowledge and listening, or any other language skill, is a clear notion of what is involved in being lexically competent in a foreign language. A further motivation behind the study therefore springs from the need to gain more in­sight into the nature of learners’ vocabulary knowledge. As evidenced in the research literature, the field suffers from a lack of consensus as to ways of defining learners’ vocabulary knowledge, partly due to the complexity and multi-dimensionality of the construct. Very often the relationship be­tween vocabulary knowledge and L2 performance has been addressed simply from the perspective of vocabulary size. However, as other dimensions of learners’ vocabulary knowledge have been recognised, notably the dimension of depth, we need to empirically investigate how such dimen­sions interact and how they can make individual contributions to learners’ language use.
1.2 Aims and research questions
The overriding aim of the thesis is to empirically investigate the relationships between

depth and breadth of vocabulary knowledge, and
vocabulary knowledge and listening comprehension in English as a foreign language.

The point of departure for this investigation is the construct of vocabulary knowledge, specifically depth of vocabulary knowledge. Although the notion of depth in L2 learners’ vocabulary has re­ceived an increasing degree of attention in recent vocabulary research, the construct severely lacks conceptual clarity. For this reason an analytic aim of the thesis is to provide a clear and consistent theoretical framework for describing and operationalising the construct of depth of vocabulary knowledge. This is done by drawing on research within the field of L2 vocabulary acquisition and testing. The analytic aim then serves as a prerequisite for empirically investigating the following two main research questions:

To what extent are EFL learners’ depth and breadth of vocabulary knowledge interrelated?
To what extent is vocabulary knowledge associated with successful listening comprehension in English as a foreign language?

While the first research question addresses the interrelationship between two dimensions of learn­ers’ vocabulary knowledge, namely a qualitative and quantitative dimension, the second research question is concerned with the extent to which these two dimensions will contribute to successful listening comprehension in English as a foreign language. The above research questions will be addressed through an empirical study comprising 100 Danish advanced learners of English. The theoretical basis and the methodology of this study will be introduced below.
1.3 Theoretical basis
Although the present study draws on research in different fields, it is first and foremost a study rooted within the field of second language vocabulary knowledge and acquisition. The widely rec­ognised theoretical distinction between depth and breadth of vocabulary knowledge will serve as a theoretical basis for reviewing different ways of defining and operationalising L2 learners’ vocabu­lary knowledge and for empirically investigating the relationship between quantitative and qualita­tive aspects of learners’ vocabulary knowledge and their listening comprehension.

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In exploring whether vocabulary knowledge is associated with successful listening comprehension in L2, the study also draws on theory and research from the field of L1 and L2 listening. Prevalent theoretical models of listening and listening comprehension will be outlined, and factors assumed to influence successful listening will be described, but this account is far from exhaustive and will only serve as a backdrop for examining the role of vocabulary in listening comprehension. This will furthermore be evident from the theoretical framework developed to describe and explore the rela­tionship between vocabulary knowledge and listening comprehension in the study. This framework draws on concepts from vocabulary as well as listening research, but the pivotal factor of the framework is vocabulary knowledge, emphasising that this is the main area of research in the study.
In attempting to operationalise vocabulary knowledge and develop instruments that can tap learn­ers’ depth of vocabulary knowledge within the context of the present research design, the study furthermore draws on concepts from testing theory and language testing research. However, the study will limit itself to primarily draw on research within the field of vocabulary testing and in particular focus on the assessment of depth of vocabulary knowledge. As will become evident, depth of vocabulary knowledge is frequently conceptualised in relation to what is made possible by assessment instruments, and the construct often becomes an artefact of the instruments used to as­sess it. This means that an important aspect of reviewing how this construct has been defined in various research contexts is to examine the way in which it has been operationalised. In view of this, concepts mainly related to vocabulary testing will be drawn upon in the present study.
In addition to this, it is important to note that the vocabulary tests developed in the study are in­tended entirely as research tools that can be used for the investigation of learners’ vocabulary knowledge within the context of the present research design. No attempts have been made to de­velop generic and practical vocabulary tests that might be used for other kinds of research or peda­gogical purposes.
1.4 Data and methodology
The empirical study comprises 100 Danish EFL learners who are all first-year students of English at the Copenhagen Business School. These participants are given a range of tests intended to tap the depth and breadth of their vocabulary knowledge as well as their listening comprehension in Eng­lish. While some of the tests are standardised measures of vocabulary size and listening comprehen­sion, others have been designed specifically for the present study to assess the participants’ depth of vocabulary knowledge. Hence, a central aspect of the methodology is the operationalisation of depth of vocabulary knowledge. Different theoretical approaches to the construct will be discussed and these will serve as a basis for operationalising the construct from two distinctly different per­spectives.
The quantitative data collected through these tests will be subjected to different kinds of statistical analyses to explore relationships between the different variables of the study. SPSS[3] is chosen as the statistical program used for the analysis of the data and the principal statistical methods will be correlational and multiple regression analyses.
As noted above, very little research has been done on the relationship between vocabulary know­ledge and listening comprehension in L2 and none of this research has addressed the role of depth of vocabulary knowledge in listening. This means that there is little solid ground for the present study to build on and it must therefore be characterised as an exploratory study.
1.5 Structure of the thesis
The thesis falls in two main parts. The first part, comprising Chapters 2 and 3, provides the theoreti­cal background for the thesis, while the second part, comprising Chapters 4 to 7, describes the theo­retical framework of the empirical study as well as the research design, and presents and discusses the results of the study. Although Chapter 4 is included in the empirical part, it can be viewed as a bridge between the two parts of the thesis. This will become evident from the description of the chapters below.
Chapter 2 constitutes the main theoretical chapter of the thesis. This chapter provides an account of different ways in which the constructs of depth and breadth of vocabulary knowledge have been defined and operationalised in the research literature. Furthermore, the chapter presents two com­prehensive conceptualisations of lexical competence and ability that attempt to integrate different dimensions of vocabulary of knowledge and explain their interrelationships.
Chapter 3 examines the role of vocabulary knowledge in listening comprehension. While the first part of the chapter presents key concepts related to listening, the sec­ond part focuses explicitly on the role of lexis in listening comprehension. This includes a brief description of word recognition models, followed by a more elaborate review of findings from empirical studies investigating the relationship between vocabulary knowledge and listening comprehension in L2.
Chapter 4 outlines the theoretical framework underpinning the empirical study. Drawing on theo­retical approaches and empirical findings dealt with in Chapters 2 and 3, the key constructs of the study will be defined and the rationale for including them will be provided. Moreover, the chapter proposes a framework for describing the relationship between vocabulary knowledge and listening comprehension and presents a number of more specific research questions that will be addressed in the study.
Chapter 5 presents the research design of the study, describing how the theoretical framework is operationalised. This includes information about participants, research instruments, the data collec­tion and the data analyses. Furthermore, a pre-testing phase involving native speakers of English will be described and the results of a pilot study will be reported. 
Chapter 6 describes the statistical analyses conducted and presents the results of the study in six phases. These phases address the various, specific research questions of the study.
Chapter 7 interprets the findings of the study, discusses implications for theory and assessment and suggests directions for future research. Furthermore, the chapter addresses a number of limitations of the study and includes suggestions for further analyses of the data collected.
Chapter 8 sums up the main findings and contributions of the thesis.

[1] The concepts of depth and breadth of vocabulary knowledge will be defined in the chapters to come. However, at this point, it should be noted that the terms breadth of vocabulary knowledge and vocabulary size will be used interchangeably in the thesis.
[2] No distinction will be made between English as second language and English as foreign language (EFL). The terms second language and foreign language will be used interchangeably.
[3] Statistical Package for the Social Sciences