Chapter 1 Introduction 1.1 Research Background 1.2 Regular and Irregular Forms in English 1.3 Research Questions and Significance 1.4 Organization of the Dissertation Chapter 2 The Theoretical Framework 2.1 The Single-Mechanism Approach 2.2 The Dual-Mechanism Approach 2.3 Diagnostic Devices Chapter 3 Literature Review 3.1 Child First Language Acquisition 3.2 Adult First Language 3.3 First Language Disorders 3.4 Second Language Acquisition Chapter 4 The Past Tense Production Task 4.1 Method 4.2 Results 4.3 Discussion Chapter 5 The Visual Lexical Decision Task 5.1 Method 5.2 Results 5.3 Discussion Chapter 6 The Masked Priming Task 6.1 Method 6.2 Results 6.3 Discussion Chapter 7 General Discussion 7.1 Frequency Effects 7.2 Phonological Similarity Effects 7.3 The Role of Regularity 7.4 The Role of Learners Factors 7.5 Advantages of the Dual-mechanism Models 7.6 Problems with the Current Models Chapter 8 Concluding Remarks 8.1 Major Findings 8.2 Implications 8.3 Limitations 8.4 Final Words Appendix 1 The Proficiency Test Appendix 2 The Real Verbs in the Production Task Appendix 3 The Familiarity Rating Task in the Production Task Appendix 4 The Target Real Verbs in the Production Task Appendix 5 The Real Verbs in the Visual Lexical Decision Task Appendix 6 The Familiarity Rating Task in the Visual Lexical Decision Task Appendix 7 The Target Real Verbs in the Visual Lexical Decision Task References Index