Concept Mediation Model VS Word Association Model

These two models were proposed by Potter et al in 1984.

The Word Association Model (WAM) suggests that the lexicon of the L1 is linked to a concept but the lexicon of the L2 is linked to the lexicon of the L1, not the concept. So an L2 learner would simply think of the word in the L1 and then connect it to the word in the L2. No other processing takes place.

Concept Mediation Model (CMM) on the other hand believes otherwise. The focus on this model is on conceptual understanding. This model believes that the lexicon of both languages are linked through concepts. Hence when a L2 learner wishes to retrieve a word in the L2, they think of it in the L1, then relate it to the concept and the concept relates back to the word in the L2.

Here is the WAM and CMM models visually:

Reversed Hierarchical Model

The Revised Hierarchical Model (RHM) is another model of mental representation in the bilingual mind. It is the revised model by Kroll & Stewart in 1994 and combines both aspects of the CMM and WAM. The RHM believes that in the initial stages of L2 acquisition, the brain uses the WAM as learners in L2 classrooms tend to learn new words by comparing it against the lexicon of their L1. However as their proficiency of the L2 increases, the brain evolves and they begin to use the CMM to store the lexicon. This is particularly useful when more experienced L2 learners come across expressions that do not exist in their L1. The CMM allows them to store these by developing new concepts. These concepts include grammar as the grammar system of an L1 and L2 may be different and translating word for word in such cases would result in ineffective communication.

Shared Memory Theory VS Memory Independence Theory

In discussing these two theories, the distinction between two categories of bilinguals is important; Compound Bilinguals and Coordinate Bilinguals. Compound Bilinguals are defined as bilinguals who learn two language in the same context where they are used concurrently. This can be from birth, in bilingual household, and can also be bilinguals coming from a bilingual education system where there is a focus on both languages such as immersion programs. Coordinate bilinguals are defined as Learning two languages in 2 different environments that never overlap. These refer mostly to older learners who learn the L2 purely academically, and have little use for the language outside of the classroom.

The Shared Memory Theory and Memory Independence theory is another set of ways in which the brain handles languages. It is similar to the RHM as proficiency determines which theory a L2 learners mind is more adjusted to however they differ as well because the focus is not on how memory is retrieved as it was in the CMM or WAM (4.1.1) and  RHM (4.1.2) but on how it is stored. In the Shared Memory Theory, compound bilinguals are more capable of alternating between their languages with ease as the theory believes both languages share a single memory store for both languages that enable them to work closely together. The Memory Independence hypotheses however believes that each language in the brain has its own individual memory systems. Thus the storage and operation of each language is independent. This hypotheses is associated most with coordinate bilinguals who tend to have difficulty code-switching.