The study of the mental lexicon deals with how words are acquired, comprehended, organized, stored, retrieved, and produces. The term “mental lexicon” is used interchangeably with what some scholars refer to as “internal lexicon” (Bonin, 2004). It involves the different processes and activations done in the brain in order to store the words and form an internal memory which functions as a mental dictionary. Psychologist and linguists who are concerned with this study believe that words are stored in relation to their phonological, semantic, syntactic and even orthographical features.
Early studies in this field were established by the end of the 1960s. The major focus of the studies was on the comprehension and production of the words. Most of the studies were oriented to psychology. The introduction of this concept into linguistics shifted the attention to the phonological, semantic, and syntactic representations in the mind. Aitchison (1994) described mental lexicon as the permanent human dictionary in which words and their meanings are stored in the brain. On the other hand, Richards (2000) described mental lexicon as the organized mental representations of the concepts and knowledge which are related to the words. There are three scopes of word knowledge; phonological, morphological, syntactic, and semantic.
I. Phonological Knowledge
The focus on the phonological mental memory was first initiated by Paul Meara (1980). He argued that the organization of words in memory depend on the phonological knowledge of the words in second language acquisition. However, in first language acquisition the memory depends on the semantic knowledge. Mear (1980) conducted a study on lexical performance in first language and second language. The study test native speakers and second language learners’ lexical abilities. The responses of the native speakers were noticeably different from those of the second language learners. In other words, the contribution of second language learners indicated that their mental lexicon depends greatly on the phonological representation of the words. Accordingly, words are mostly organized and associated by their similarities in pronunciation.
The same conclusion was also reached in another study done by Zhang (2004). He applied his study on two groups. The first group included forty Chinese students who were learning English as a second language. The second group of participants involved nineteen native speakers of English language. The study proved that learners of the second language depend more on phonological knowledge in their comprehension, organization, and production. However, Singleton (1999) and Soderman (1993) argued that mental lexicon organization is similar in both first language and second language acquisition. Singleton based his studies on a project which proved that native and second language learners order their word knowledge by their semantic associations.