پوتامن و درک جملات زبان اول و دوم: شواهدی از تصویربرداری تشدید مغناطیسی عملکردی (مقاله علمی وزارت علوم)
درجه علمی: نشریه علمی (وزارت علوم)
آرشیو
چکیده
اگرچه پوتامن یک ساختار زیرقشری محسوب می شود، مطالعات تصویربرداری دخالت ناحیه پوتامن چپ را در کارکردهای زبانی مانند پردازش زبان دوزبانه ها نشان داده اند. برخی مطالعات نیز به نقش پوتامن راست در عملکردهای زبانی مرتبه بالاتر اشاره کرده اند. هدف از بازتحلیل حاضر، بررسی نقش پوتامن چپ و راست در درک جملات زبان اول و دوم در افراد دوزبانه با استفاده از روش تصویربرداری تشدید مغناطیسی عملکردی (fMRI) است. بدین ترتیب، تعداد 36 نفر دوزبانه ترکی-فارسی (21 زن و 15 مرد) که زبان دوم شان را در سن 7 سالگی و به هنگام ورود به مدرسه به طور رسمی آموخته بودند، به روش هدفمند در سال 1398 انتخاب شدند. شرکت کنندگان یک آزمون شنیداری قضاوت دستوری بودگی با پارادایم زبان گردانی جایگزین را اجرا کردند. به دنبال شناسایی فعالیت دوجانبه پوتامن در سطح کل-مغز در FSL، درصد تغییر سیگنال به عنوان معیار «شدت» برای هر شرکت کننده استخراج و در نرم افزار SPSS-26 تجزیه و تحلیل آماری شد. در سطح کل-مغز، نتایج نشان داد که ناحیه پوتامن در نیمکره های چپ و راست در درک نحوی جملات در حین ارائه همزمان محرک های زبان اول و دوم دخالت دارد. علاوه براین، صرف نظر از نوع نیمکره فعال، معناداری اثر دستوری بودگی برای زبان اول و حساسیت بیشتر به محرک های نادستوری زبان اول در مقایسه با محرک های نادستوری زبان دوم مشاهده شد که می تواند دال بر اثر استاندارد تسلط زبان باشد.Putamen and L1-L2 sentence comprehension: Evidence from functional magnetic resonance mapping
The putamen is a subcortical structure. However, neuroimaging studies have demonstrated the involvement of the left putamen in other language functions such as bilingual language processing. Some studies have also shown the role of the right putamen in higher-order language functions. The present reanalysis aims to investigate the role of the bilateral putamen during the L1-L2 sentence comprehension in bilinguals using functional magnetic resonance imaging (fMRI). Hence, 36 Turkish-Persian bilinguals (21 females and 15 males), who had acquired their second language at the age of seven after entering school, were selected in a purposive sampling method to perform an auditory grammaticality judgment task within an alternative language switching paradigm. After detecting the activity of the bilateral putamen at the whole-brain level, in FSL, percent signal change was extracted per participant as an intensity measure and analyzed statistically in SPSS. At the whole-brain level, the findings demonstrated that the bilateral putamen was involved in the comprehension of syntactic structures during the alternating presentation of L1 and L2 stimuli. In addition, regardless of the hemisphere involved, the significant grammaticality effect for L1 as well as the increased sensitivity for L1-violation stimuli compared to L2-violation stimuli may imply the standard language dominance effect also in the putamen.
Keywords: Bilingualism, Sentence comprehension, Putamen, L1, fMRI
Introduction
Subcortical structures are considered a key component in language processing in bilinguals. Basal ganglia are a group of subcortical structures found deep within the White Matter of the brain and have extensive connections with the cerebral cortex, especially Broca's area and speech motor cortex. These nuclei include Putamen, Caudate, Pallidum, substantia nigra and subthalamic. Nowadays, the involvement of Putamen in production processes is evidenced, nevertheless, very little is known about the contribution of this region in understanding syntax in bilinguals. To our knowledge, no studies have examined the role of Putamen in syntactic processing in bilinguals. Here, we aimed to explore it within an alternative language switching paradigm.
To address this gap, the current reanalysis focuses on the following research question.
How is the performance of bilateral Putamen during L1-L2 syntactic processing?
To answer this research question guiding this study, a bilingual task with alternating language switching paradigm were developed. In this task, brain imaging was performed using event-related fMRI while the participants listened to a total of 128 sentences in two Turkish and Persian languages.
Materials and methods
To allow for reliable ROI-based analysis, 36 right-handed and balanced Turkish-Persian bilingual students were recruited to participate in this study. All participants were native speakers of Turkish and learned Persian at school from the age of seven. Participants' language proficiency levels were assessed by the Bilingual Dominance Scale (BDS) and no significant difference was observed between Turkish and Persian (i.e., between L1 and L2) in language dominance. During a bilingual grammaticality judgement task, participants heard 128 test sentences (64 in L1 and 64 in L2, with 50% violation per language) and made their judgment by pressing a button. Stimuli were presented using the Psychtoolbox in MATLAB via headphones. Stimuli were randomized for each condition, but alternated in a fixed sequence for language. MRI data were collected in NBML, Tehran, Iran, using a Siemens Prisma 3T scanner with a 20-channel head coil. For each participant, a high-resolution T1-weighted anatomical scan was acquired (TR = 1800msec, TE = 3053 msec, flip angle: 7°, 192 axial slices, slice thickness = 1 mm, field of view (FOV) = 256 mm2, 256 × 256 acquisition matrix, voxel size: 1×1×1 mm). After the anatomical scan, participants underwent a 21.5-min fMRI scan that used a whole brain echo planar imaging (EPI) sequence (TE: 30 ms, TR: 3000 ms, flip angle: 90°, slice thickness: 3 mm, voxel size: 3×3×3 mm, matrix size: 64×64, FOV: 192 mm2, 430 volumes and 45 axial slices per volume). Processing of the fMRI data was carried out using FEAT in FSL. Preprocessing steps included motion correction, slice-timing correction, non-brain removal using BET, spatial smoothing (6 mm FWHM), normalization, temporal filtering (with sigma = 50.0 s), and exploratory ICA-based data analysis. Statistical analyses of fMRI data were conducted using general linear modeling (GLM), as implemented in FSL. Z statistic images were thresholded using clusters determined by Z > 2.6 and a (corrected) cluster significance threshold of P < 0.05. After detecting the Cerebellum activation in the whole-brain analysis, percent signal changes were extracted as an intensity measure in this brain region. All statistical analyses were conducted in IBM SPSS Statistics 26.
Discussion of results and conclusions
The present reanalysis investigate the contribution of Putamen in Turkish-Persian participants during processing syntax. Our research question concerns whether there are differences in syntactic processing between L1 and L2 in bilateral Putamen in non-native participants. At the whole-brain level, the findings indicated that the bilateral Putamen is involved in modulating the syntactic aspects of language, supporting the previous pathological studies on Putamen as well as its association with cortical areas in the realm of bilingualism. Another crucial point is regarding the significant effect of grammaticality in L1 and significant differences between L1-ungrammatical and L2-ungrammatical sentences, irrespective of the involved hemisphere. This is in line with the behavioral performance of present sample in which bilinguals had longer reaction time and more errors for L1 which was leading to more brain activations. This could be arguably because of the standard language dominance effect placed on L1, as mentioned by Declerck & Koch (2023), demonstrating that the present population may have relied more on their L1 than L2. Accordingly, using Chinese-English bilingual speakers, Wang and his colleagues (2009) found that sustained and transient language control induced differential activation patterns, and that sustained and transient activities in the human brain modulate the behavioral costs during switching-related language control. Thus, it is reasonable to say that in mixed-language blocks, balanced bilinguals performed better in L1 than in L2. In sum, based on current sample and task, we propose that bilinguals who had learnt L2 at the age of seven when entering school have employed the bilateral Putamen during processing syntax with standard language dominance effect (i.e., better performance in L1 than in L2).
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