Bilingual interactive activation plus

According to the BIA+ model shown in the figure, during word identification, the visual input activates the sublexical orthographic representations which simultaneously activate both the orthographic whole-word lexical and the sublexical phonological representations. Both whole-word orthographic and phonological representations then activate the semantic representations and language nodes which indicate membership to a particular language. All of this information is then used in the task/decision subsystem to carry out the remainder of the task at hand. The two subsystems are further described by the assumptions associated with them below.

The integrated lexicon assumption describes the interactivity of the visual representation of word or word parts and orthography, the phonologic or auditory component of language processing, and the semantic or significance and meaning representations of words.[4] This theory was tested with orthographic neighbors, words of the same length that differ by one letter only (e.g. BALL and FALL). The number of target and non-target language neighbors influenced target word processing in both the primary language (L1) and the secondary language (L2).[5] This cross-language neighborhood effect was supposed to reflect a co-activation of words whatever the language they belong to, that is a lexical access that is language nonselective. Both target and nontarget languages can be automatically and unconsciously activated even in a pure monolingual mode. This does not imply, however, that there may not be features unique to one language (i.e. the use of different alphabets) or that, at the semantic level, there are no shared features.

This assumption states that language nodes/tags exist to provide a representation for the language of membership based on the information from upstream orthographic and phonological word ID processes. According to the BIA+ model, these tags have no effect on the activation level representation of words.[1] The focus of activation of these nodes is postlexical: the existence of these nodes enables bilingual individuals not to get too much interference from the nontarget language while they process one of their language.

Parallel access assumes that language is nonselective and that both potential word choices are activated in the bilingual brain when exposed to the same stimulus. For example, test subjects reading in their second language have been found to unconsciously translate to their primary language.[6] N400 stimulus response activation measurements show that semantic priming effects were seen in both languages and an individual cannot consciously focus their attention to only one language, even when told to ignore the second.[7] This language nonselective lexical access has been shown during semantic activation across languages, but also at the orthographic and phonological levels.

The temporal delay assumption is based on the principle of resting potential activation which reflects the frequency of word use by the bilingual such that high frequency words correlate to high resting level activation potentials, and words used with little frequency correlate to low resting level activation potentials. A high resting potential is one that is less negative or closer to zero, the point of activation, and therefore needs less stimuli in order to become activated. Because the less commonly used words of L2 have a lower resting level activation, L1 is likely to be activated before L2 as seen by N400 ERP patterns.[8]

This resting level activation of words also reflects the proficiency level of bilinguals and their frequency of usage of the two languages. When a bilingual’s language proficiency is lower in L2 than L1, the activation of L2 lexical representations will be further delayed as more extensive or higher-level brain activation is necessary for language control.[4] Both low and high proficiency bilinguals have parallel activation of the word representations, however the less proficient language, L2, becomes active more slowly contributing to the temporal delay assumption.

The locations of many of the word identification processing tasks have been determined with fMRI studies. Word retrieval is localized in Broca's area of the prefrontal cortex,[9] whereas storage of information is localized in the inferior temporal lobes. Globally, the same brain areas have been shown to be activated across the L1 and L2 in highly proficient bilinguals. Some subtle differences between L1 and L2 activations emerge though when testing lower proficient bilinguals.

The task/decision subsystem of the BIA+ model determines which actions must be executed for the task at hand based on the relevant information that becomes available after word identification processing.[1] This subsystem involves many of the executive processes including monitoring and control associated with the prefrontal cortex.

Action plans that meet the task at hand are executed by the task/decision system on the basis of activation information from the word identification subsystem.[7] Studies that tested bilinguals with homographs showed that conflicts between target and non-target language readings of the homographs still led to a difference in activation between it and a control, implying that bilinguals are not able to regulate activation in the word identification system.[10] Therefore, the action plans of the task/decision system have no direct influence on activations of word identification language subsystem.

The neural correlates of the task/ decision subsystem consist of multiple components that map onto different areas of prefrontal cortex responsible for executing control functions. For example, the general executive functions of language switching have been found to activate the anterior cingulate cortex and dorsolateral prefrontal cortex areas.,[11][12]

Translation, on the other hand, requires controlled actions in language representations and has been associated with the left basal ganglia,[12][13] The left caudate nucleus has been associated with control of in-use language,[14] and the left mid-prefrontal cortex is responsible for monitoring interference and suppressing competing responses between languages.,[13][15]