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REVIEW ARTICLE
Year : 2019  |  Volume : 32  |  Issue : 1  |  Page : 38-44

Language processing in a bilingual child


1 Phoniatrics Unit, Otorhinolaryngology Department, Ain Shams University, Cairo, Egypt
2 Phoniatrics Unit, Otorhinolaryngology Department, Cairo University, Cairo, Egypt
3 Phoniatrics Unit, Otorhinolaryngology Department, Menoufia University, Menoufia, Egypt
4 Phoniatrics Unit, Otorhinolaryngology Department, Menoufi University, Ministry of Health, Egypt

Date of Submission01-Apr-2018
Date of Acceptance01-Jun-2018
Date of Web Publication17-Apr-2019

Correspondence Address:
Fatima M Al-Sharif
Tanta, El-Gharbia
Egypt
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/mmj.mmj_151_18

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  Abstract 


Objectives
To review the language processing, 'central and linguistic processing,' in bilingual children. The age of second language acquisition, a factor which may impact language processing, was also reviewed.
Data sources
Medline databases (PubMed, Medscape, and Science Direct) using the terms 'bilingual' or 'bilingualism' with the word 'children' as the search criteria. The resulting materials available in the internet from 1980 to 2017 were further screened for the terms 'processing,' 'cognition,' or 'age of acquisition.'
Study selection
Our refined search included 124 articles and book's chapters out of which 83 met our selection criteria. Those data related to late bilingualism were excluded.
Data extraction
If the studies did not fulfill the inclusion criteria, they were excluded. Study quality assessment included whether ethical approval was gained, eligibility criteria specified, adequate information, and defined assessment measures were made.
Data synthesis
Significant data were collected. It was heterogeneous. Thus, a structured review was performed with the results tabulated.
Conclusion
An unresolved issue in bilingualism is how different languages are represented in the brain and which cognitive mechanisms are required to regulate their use. In learning a second language, the brain has to build on a neural network that enables the segregation of the new language from the native one. A bilingual child can create languages' activation and inhibitory links at the lexical and the morphological level and also can develop the ability to select a word and its syntactic characters correctly.

Keywords: age of acquisition, bilingual brain, bilingual child, bilingualism, code mixing, code switching, cognitive processing, second language


How to cite this article:
Baraka M, El-Dessouky H, Ezzat E, Al-Sharif FM. Language processing in a bilingual child. Menoufia Med J 2019;32:38-44

How to cite this URL:
Baraka M, El-Dessouky H, Ezzat E, Al-Sharif FM. Language processing in a bilingual child. Menoufia Med J [serial online] 2019 [cited 2019 May 21];32:38-44. Available from: http://www.mmj.eg.net/text.asp?2019/32/1/38/256086




  Introduction Top


One of the most remarkable functions of the human cortex is the generation and comprehension of language, which may be a more complex process when dealing with more than one language. Systematic investigations of child bilingualism began ~100 years ago with a careful study [1].

The broad definition of bilingual person is a speaker of one language who can speak in another language. This definition fits the person who speaks two languages equally fluently. It also fits a person who has not yet acquired a full grammar for a language, but may still be able to construct meaningful utterances in that language. The narrow definition of this term describes a person with a native-like control of two languages. This would exclude a beginning language student and those who easily comprehends, but does not produce utterances in a second language and who has a 'foreign accent.' It only implies that a person has two mother tongues [2].

Early bilingualism is a term that refers to one of the two subtypes: either simultaneous or successive. Simultaneous early bilingualism means a child who learns two languages at the same time from birth. This generally produces a strong bilingualism. Successive (or consecutive) early bilingualism refers to a child who has already partially acquired a first language and then learns a second language early in childhood. This also produces a strong bilingualism because the second language is learned at the same time as the child learns to speak [3].

Late bilingualism refers to bilingualism when the second language is learned after the age of 6 or 7 years. Late bilingualism is a consecutive bilingualism which occurs after the acquisition of the first language (after complete language development). With the first language already acquired, the late bilingual uses his experience to learn the second language [4].

The importance of being bilingual or the effects of bilingualism has been linked to both cognitive advantages as well as disadvantages in children's cognitive development. Researches have indicated increased concentration abilities among bilinguals, and found a strong connection between the level of bilingual proficiency and cognitive flexibility. Similarly, researchers mentioned enhanced executive functioning amid bilinguals. However, some studies have implied the opposite, as bilinguals have shown a delay in grammatical structure and vocabulary acquisition. Many studies suggest a positive relationship between bilingualism and cognitive development (far outnumber the ones indicating the opposite) where social networks and language valorization play important roles in determining the level of bilingual proficiency [5].

A deeper understanding of both language and its principles governing brain organization can come from investigating the degree to which language affects the relevant neural system. 'Language regions' of the brain are specialized for the symbolic representation of communication, rather than being specialized for spoken versus written language. Bilingual Neuroscience and Cognitive Psychology have a leading role in understanding languages confusions. Neuroscience researches show that the brain mechanisms that allow bilinguals to achieve better switching between several tasks correlates with the activation of language networks in bilinguals, but not in monolinguals [6].

In the current study, we aimed to review the literature regarding central language processing as well as linguistic processing in bilingual children. The age of second language acquisition as a factor, which may impact language processing, was also reviewed.


  Materials and Methods Top


Search strategy: We reviewed papers on language processing in bilingual child Medline databases (PubMed, Medscape, and Science Direct) and also materials available on the internet from 1985 to 2017. We used 'bilingualism' as a main term of search plus one of these items: brain areas/processing/linguistic processing/universal language neural network/mapping lexical representations/the unitary language system hypothesis/early and late bilingualism/quantitative language assessment as searching guides and terms/age of acquisition.

Study selection

All the studies were independently assessed for inclusion. They were included if they fulfilled the following criteria:

  1. Original work study.
  2. Well designed with clear selection criteria and clear results.
  3. Published in English language.
  4. Published in peer-reviewed journals.
  5. Focused on bilingualism and second language development.
  6. If a study had several publications on certain aspects, we used the latest publication giving the most relevant data.


Data extraction

If the studies did not fulfill the above criteria, they were excluded. The analyzed publications were evaluated according to evidence-based medicine criteria using the classification of the U S Preventive Services Task Force.

U S Preventive Services Task Force

Level I: evidence obtained from at least one properly designed, randomized, controlled trial.

Level II-1: evidence obtained from well-designed controlled trials without randomization.

Level II-2: evidence obtained from well-designed cohort or case–control analytic studies, preferably from more than one center or research group.

Level II-3: evidence obtained from multiple time series with or without the intervention. Dramatic results in uncontrolled trials might also be regarded as this type of evidence.

Level III: opinions of respected authorities, based on clinical experience, descriptive studies, or reports of expert committees.

Quality assessment

The quality of all the studies was assessed. Important factors included study design, attainment of ethical approval, evidence of power calculation, specified eligibility criteria, appropriate controls and adequate information and specified assessment measures. It was expected that the confounding factors would be reported and controlled for and appropriate data analysis made in addition to an explanation of missing data.

Data synthesis

A structured systematic review was performed with the results tabulated.


  Results Top


On the basis of our selection criteria, 37 well-designed studies were included. Studies which were not original or poorly designed were excluded from our review.

Regarding language processing, four studies showed that the data were much heterogeneous especially for the age of included participants, types of L1/L2 languages of bilingualism (e.g. English, Spanish, French, etc.), and assessment tools [MRI, functional near-infrared spectroscopy (fNIRS), positron emission tomography (PET) scan, etc.].

However, 10 of the studies showed that there are no language-specific areas for L2 in bilinguals. However, based on the task 'whether language production, word comprehension, sentence comprehension.etc.' there is increased activation of certain language areas in the brain. Also, there is activation of certain subnetwork pathways during the L2 different tasks as shown in [Table 1].
Table 1: Central language processing

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About 11 studies that concerned linguistic skills were much heterogeneous. Evaluation tests as well as assessment tools differ completely between studies. However, for most, there was no group difference between monolingual and bilingual children on either visual or auditory tasks. In situations of simultaneous competition, phonologically overlapping items appear to compete between languages. This supports the parallel activation hypothesis of both languages. Unequal exposure to the minor language in bilinguals leads to retardation of the minor language. Also one study that supports the performance of bilingual children on TOM (for thinking and memory skills) was significantly higher compared with the performance of monolingual peers [Table 2].
Table 2: Linguistic skills

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Regarding age of acquisition 13 of the available studies showed that here is higher activation of language areas through late language acquisition than that for early language acquisition children [Table 3].
Table 3: Age of acquisition

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  Discussion Top


A primary question of this article is whether central language processing in bilinguals differs from those in monolinguals. Unfortunately, the research in this perspective is much heterogeneous regarding the nature of bilingualism (e.g. Spanish, English, French, Chinese, etc.) and also by the tested task (e.g. cognition, word production, and comprehension).

PET is a technique that measures the physiological function by looking at the blood flow, 'for example, regional cerebral blood flow (rCBF),' metabolism, neurotransmitters, and radiolabelled drugs. However, it provides less accurate anatomical data. So, many scanners started to run a combined PET/MRI scan to combine functional/anatomical data [26].

The landmark PET investigation by researchers used a word repetition task in native/ first language and second language to explain if the production of a second language involved the same neural substrates as in the first language. This study was conducted on native English speakers who learnt French after the age of 5 years. They demonstrated that the pattern of regional cerebral blood flow distribution was similar across the two languages. By suggestion of that repetition involves largely overlapping neural structures, the only difference was found in the selective activation of the left putamen [7].

Other PET studies, addressing the question whether memory processing in two languages belongs to different linguistic groups, use common neural systems. They looked for (shared and nonshared) neural substrates in a paired-word association paradigm for Finnish and English. Results showed differential activations in Broca's area and in the cerebellum as well as in the angular/supramarginal gyri according to the language used [8].

MRI was another extensively used assessment tool of central language processing in bilinguals. The advantage of MRI was the lack of radiation exposure with many variable techniques that can provide both anatomical and functional data. Brain scans of bilingual individuals found greater gray-matter density in the inferior parietal cortex, an area in the brain's language-dominant left hemisphere. The density was most pronounced in people who were highly proficient in a second language and in those who learned a second language before the age of 5 years [9].

An alternative technique of MRI is functional MRI (fMRI), which can provide both anatomical and functional data. The fMRI analyses revealed that both monolinguals and bilinguals showed increased activation in classic language areas [e.g. left inferior frontal cortex (LIFC)]. An important difference between monolinguals and bilinguals was that bilinguals had a significantly greater increase in the blood oxygenation level [12].

These results were also recruited by researchers who investigated a group of Spanish/Catalan bilingual versus Spanish monolinguals. Taken together, these data suggest that early bilingualism shapes the brain for cognitive processes in sentence comprehension even in their native language. On the other hand, they indicate that brain overactivation in bilinguals is not constrained to a specific area [14].

Diffusion tensor imaging is an MRI-based neuroimaging technique which makes it possible to estimate the location, orientation, and anisotropy of the brain's white-matter tracts. Using diffusion-weighted MRI tractography techniques and a network-based statistic procedure, Garcia-Penton et al. [15], in his work conducted in Spanish–Basque either monolinguals or bilinguals, found two structural subnetworks more connected by white-matter tracts in bilinguals than in monolinguals, confirming white-matter brain plasticity in bilinguals. These results suggest that bilinguals develop specialized language subnetworks to deal with the two languages [15].

Measurement of relative changes in hemoglobin concentration through the use of light attenuation at multiple wavelengths during differences in the absorption spectra of deoxy-hemoglobin and oxy-hemoglobin allow the functional near-infrared spectroscopy (fNIR or fNIRS) takes advantage of the optical window as skin, tissues, and bones are mostly transparent to near-infrared light [27].

While fNIRS cannot record deep into the human brain (about 4 cm depth), it has good spatial resolution that is excellent for studies of human higher cognition and language. Also it has better temporal resolution than fMRI. Unlike the large size of fMRI, fNIRS is very small, highly portable (the size of a desktop computer), and particularly child friendly [11].

Application of fNIRS showed that monolingual and bilingual children have activation in the same language areas classically observed in adults, including the left superior temporal gyrus and the LIFC. However, activation of the left superior temporal gyrus was observed earlier and remained with stable activity over time. The LIFC showed greater increase in neural activation in older babies, corresponding to the age of catching the first universal milestone of language acquisition. This concludes that bilingual babies maintained linguistic sensitivity opens for a longer time [13].

Linguistic abilities seem to be sensitive to the age of exposure to a second language. The understanding of these age effects is complicated by the fact that the different components of language have different critical periods.

The question, 'Is there is a critical age of acquisition that can reshape the language areas in bilingual brains during second language?' remains partially replied. According to researchers, comparisons of behavioral data between high-proficiency early acquisitions and high-proficiency late acquisition revealed no significant differences in L2 between the two groups. Grammatical judgment for both groups showed significantly more extensive activation involving Broca's region and subcortical structures during grammatical processing in L2. Semantic judgment for both late acquisition groups showed a bilateral greater activation in the inferior frontal areas in semantic judgment L2, with the activation of the low-proficiency late acquisition group being in Broca's area (BA 44) compared with the high-proficiency late acquisition group, which showed a more inferior frontal activation (BA 47) [22].

Researchers showed that representation of a bilingual storage increases gradually with the age of L2 acquisition. Sequential bilinguals had much variance in the number of activated fMRI voxels when compared with simultaneous bilinguals. These data suggest a gradual change from the simple representation of two languages in 'early bilingualism' to the more complex representation in 'late multilingualism' [23].

In accordance with previous results, Wei et al. [24] suggest that the structure of the human brain is reworked by the experience of acquiring a second/non-native language and when considering structural changes in bilingual brains. Age of second language acquisition, proficiency, and exposure level should all be taken into consideration [24].

In a recent study by using electrical stimulation mapping to evaluate the activation of language cortical areas in bilinguals was found to be not homogeneous. It is influenced by language acquisition time, since early-acquired languages have a greater cortical representation than those that are acquired subsequently [18].


  Conclusion Top


An unresolved issue in bilingualism is how different languages are represented in the brain and which linguistic mechanisms are required to express and regulate their use. In acquiring a second language, the brain has to build on a neural network that enables to connect the new language to the native one. The bilingual child can create languages' activation and inhibitory links at the lexical, morphological, and syntactic levels. Bilinguals can develop the ability to correct the words selection and its syntactic properties in the target language which is currently in use. As a limitation of researches on that field, low power and heterogeneity of methodology must be increased (e.g. age of participants, studied language, assessment tools, and variety of linguistic tasks). Also, most of the studies run for balanced bilinguals, that is, bilinguals who have spoken both their languages approximately equally since acquiring those languages. Unfortunately, this kind of bilingualism is not the one commonly encountered in our community. More powered researches based on strict selection criteria with more unified methodology are still required to answer the unresolved issues. Currently, no data is available regarding Arabic bilingual children. Further organized researches are warranted for Arabic children.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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