Early acquisition of sign language What neuroimaging data tell us

Associations Between Sign Language Skills and Resting-State Functional Connectivity in Deaf Early Signers

The processing of a language involves a neural language network including temporal, parietal, and frontal cortical regions. This applies to spoken as well as signed languages. Previous research suggests that spoken language proficiency is associated with resting-state functional connectivity (rsFC) between language regions and other regions of the brain. Given the similarities in neural activation for spoken and signed languages, rsFC-behavior associations should also exist for sign language tasks. In this study, we explored the associations between rsFC and two types of linguistic skills in sign language: phonological processing skill and accuracy in elicited sentence production. Fifteen adult, deaf early signers were enrolled in a resting-state functional magnetic resonance imaging (fMRI) study. In addition to fMRI data, behavioral tests of sign language phonological processing and sentence reproduction were administered. Using seed-to-voxel connectivity analysis, we investigated associations between behavioral proficiency and rsFC from language-relevant nodes: bilateral inferior frontal gyrus (IFG) and posterior superior temporal gyrus (STG). Results showed that worse sentence processing skill was associated with stronger positive rsFC between the left IFG and left sensorimotor regions. Further, sign language phonological processing skill was associated with positive rsFC from right IFG to middle frontal gyrus/frontal pole although this association could possibly be explained by domain-general cognitive functions. Our findings suggest a possible connection between rsFC and developmental language outcomes in deaf individuals.

Sign and Spoken Language Processing Differences in the Brain: A Brief Review of Recent Research

Background:

It is currently accepted that sign languages and spoken languages have significant processing commonalities. The evidence supporting this often merely investigates frontotemporal pathways, perisylvian language areas, hemispheric lateralization, and event-related potentials in typical settings. However, recent evidence has explored beyond this and uncovered numerous modality-dependent processing differences between sign languages and spoken languages by accounting for confounds that previously invalidated processing comparisons and by delving into the specific conditions in which they arise. However, these processing differences are often shallowly dismissed as unspecific to language.

Summary:

This review examined recent neuroscientific evidence for processing differences between sign and spoken language modalities and the arguments against these differences’ importance. Key distinctions exist in the topography of the left anterior negativity (LAN) and with modulations of event-related potential (ERP) components like the N400. There is also differential activation of typical spoken language processing areas, such as the conditional role of the temporal areas in sign language (SL) processing. Importantly, sign language processing uniquely recruits parietal areas for processing phonology and syntax and requires the mapping of spatial information to internal representations. Additionally, modality-specific feedback mechanisms distinctively involve proprioceptive post-output monitoring in sign languages, contrary to spoken languages’ auditory and visual feedback mechanisms. The only study to find ERP differences post-production revealed earlier lexical access in sign than spoken languages. Themes of temporality, the validity of an analogous anatomical mechanisms viewpoint, and the comprehensiveness of current language models were also discussed to suggest improvements for future research.

Key message:

Current neuroscience evidence suggests various ways in which processing differs between sign and spoken language modalities that extend beyond simple differences between languages. Consideration and further exploration of these differences will be integral in developing a more comprehensive view of language in the brain.

Age of sign language acquisition has lifelong effect on syntactic preferences in sign language users

Acquisition of natural language has been shown to fundamentally impact both one's ability to use the first language, and the ability to learn subsequent languages later in life. Sign languages offer a unique perspective on this issue, because Deaf signers receive access to signed input at varying ages. The majority acquires sign language in (early) childhood, but some learn sign language later - a situation that is drastically different from that of spoken language acquisition. To investigate the effect of age of sign language acquisition and its potential interplay with age in signers, we examined grammatical acceptability ratings and reaction time measures in a group of Deaf signers (age range: 28-58 years) with early (0-3 years) or later (4-7 years) acquisition of sign language in childhood. Behavioral responses to grammatical word order variations (subject-object-verb vs. object-subject-verb) were examined in sentences that included: 1) simple sentences, 2) topicalized sentences, and 3) sentences involving manual classifier constructions, uniquely characteristic of sign languages. Overall, older participants responded more slowly. Age of acquisition had subtle effects on acceptability ratings, whereby the direction of the effect depended on the specific linguistic structure.

White matter alteration in adults with prelingual deafness: A TBSS and SBM analysis of fractional anisotropy data

A loss of hearing in early life leads to diversifications of important white matter networks. Previous studies related to WM alterations in adult deaf individuals mainly involved univariate analysis of fractional anisotropy (FA) data and volumetric analysis, which yielded inconsistent results. To address this issue, we investigated the FA value alterations in 38 prelingual adult deaf individuals and compared the results with those obtained from the same number of adults with normal hearing by using univariate (tract-based spatial statistics) and multivariate (source-based morphometry) methods. The findings from tract-based spatial statistics suggested an increased FA value in regions such as the left cingulate gyrus, left inferior frontal occipital fasciculus, left inferior longitudinal fasciculus and superior corona radiata; however, the results indicated a decreased FA value in the left planum temporale of adult deaf individuals. While source-based morphometry analysis outlined higher FA values in regions such as bilateral lingual gyrus, bilateral cerebellum, bilateral putamen and bilateral caudate, a considerable decrease was observed in the bilateral superior temporal region of the deaf group. These alterations in multiple neural regions might be linked to the compensatory cross-modal reorganizations attributed to early hearing loss.

The Comparison of the Morphological and Syntactic Awareness Skills of Deaf and Hard of Hearing Students Regarding Agreement and Tense Categories that Exist in Verbs in Reading Activities with those of Students Without Hearing Disabilities

The difficulties in learning skills that deaf and hard of hearing students encounter stem from morphology and syntactic morphology (morpho-syntax) and it is clear that there are limited studies related to these. In this study, it is aimed at examining hearing and deaf and hard of hearing students' morpho-syntactic actions which are compatible with the Turkish Sign Language and the awareness skills of these actions in the time categories. In total 122 students; 57 deaf and hard of hearing students from secondary and high school and 65 hearing students have participated this study. The data is gathered through DMASTR and SuperLab 5 software programs where data is collected by a process with a "word reading method" and "an inclusion of agreement and tense categories in actions". In the outcome of the study it is identified that students hard of hearing had an underachievement in the agreement and tense categories compared to hearing students. At the agreement category, in terms of reading duration it is seen that deaf students' verbs with disagreement compared with verbs with agreement, they read faster. In the tense category, it is clear that deaf and hard of hearing students' accuracy rate of reading words have got similarities in the categories of past and future tenses whereas they have got inadequacies in the present tense, when the data is observed in terms of the speed of reaction and reading duration, it is seen that they are more successful in the past tense. In accordance with these findings, it is indicated that hard of hearing students have shared the same reading skills with their hearing peers whereas they had plenty of difficulties related to reading skills some of them which are from the fields of morphology and syntactic morphology, in the steps of formal education.

Age of acquisition effects differ across linguistic domains in sign language: EEG evidence

One of the key questions in the study of human language acquisition is the extent to which the development of neural processing networks for different components of language are modulated by exposure to linguistic stimuli. Sign languages offer a unique perspective on this issue, because prelingually Deaf children who receive access to complex linguistic input later in life provide a window into brain maturation in the absence of language, and subsequent neuroplasticity of neurolinguistic networks during late language learning. While the duration of sensitive periods of acquisition of linguistic subsystems (sound, vocabulary, and syntactic structure) is well established on the basis of L2 acquisition in spoken language, for sign languages, the relative timelines for development of neural processing networks for linguistic sub-domains are unknown. We examined neural responses of a group of Deaf signers who received access to signed input at varying ages to three linguistic phenomena at the levels of classifier signs, syntactic structure, and information structure. The amplitude of the N400 response to the marked word order condition negatively correlated with the age of acquisition for syntax and information structure, indicating increased cognitive load in these conditions. Additionally, the combination of behavioral and neural data suggested that late learners preferentially relied on classifiers over word order for meaning extraction. This suggests that late acquisition of sign language significantly increases cognitive load during analysis of syntax and information structure, but not word-level meaning.

The Impact of Transitional Movements and Non-Manual Markings on the Disambiguation of Locally Ambiguous Argument Structures in Austrian Sign Language (ÖGS)

Previous studies of Austrian Sign Language (ÖGS) word-order variations have demonstrated the human processing system's tendency to interpret a sentence-initial (case-) ambiguous argument as the subject of the clause ("subject preference"). The electroencephalogram study motivating the current report revealed earlier reanalysis effects for object-subject compared to subject-object sentences, in particular, before the start of the movement of the agreement marking sign. The effects were bound to time points prior to when both arguments were referenced in space and/or the transitional hand movement prior to producing the disambiguating sign. Due to the temporal proximity of these time points, it was not clear which visual cues led to disambiguation; that is, whether non-manual markings (body/shoulder/head shift towards the subject position) or the transitional hand movement resolved ambiguity. The present gating study further supports that disambiguation in ÖGS is triggered by cues occurring before the movement of the disambiguating sign. Further, the present study also confirms the presence of the subject preference in ÖGS, showing again that signers and speakers draw on similar strategies during language processing independent of language modality. Although the ultimate role of the visual cues leading to disambiguation (i.e., non-manual markings and transitional movements) requires further investigation, the present study shows that they contribute crucial information about argument structure during online processing. This finding provides strong support for granting these cues some degree of linguistic status (at least in ÖGS).

Syllable as a unit of information transfer in linguistic communication: The entropy syllable parsing model

To understand human language-both spoken and signed-the listener or viewer has to parse the continuous external signal into components. The question of what those components are (e.g., phrases, words, sounds, phonemes?) has been a subject of long-standing debate. We re-frame this question to ask: What properties of the incoming visual or auditory signal are indispensable to eliciting language comprehension? In this review, we assess the phenomenon of language parsing from modality-independent viewpoint. We show that the interplay between dynamic changes in the entropy of the signal and between neural entrainment to the signal at syllable level (4-5 Hz range) is causally related to language comprehension in both speech and sign language. This modality-independent Entropy Syllable Parsing model for the linguistic signal offers insight into the mechanisms of language processing, suggesting common neurocomputational bases for syllables in speech and sign language. This article is categorized under: Linguistics > Linguistic Theory Linguistics > Language in Mind and Brain Linguistics > Computational Models of Language Psychology > Language.

Subject preference emerges as cross-modal strategy for linguistic processing

Research on spoken languages has identified a "subject preference" processing strategy for tackling input that is syntactically ambiguous as to whether a sentence-initial NP is a subject or object. The present study documents that the "subject preference" strategy is also seen in the processing of a sign language, supporting the hypothesis that the "subject"-first strategy is universal and not dependent on the language modality (spoken vs. signed). Deaf signers of Austrian Sign Language (ÖGS) were shown videos of locally ambiguous signed sentences in SOV and OSV word orders. Electroencephalogram (EEG) data indicated higher cognitive load in response to OSV stimuli (i.e. a negativity for OSV compared to SOV), indicative of syntactic reanalysis cost. A finding that is specific to the visual modality is that the ERP (event-related potential) effect reflecting linguistic reanalysis occurred earlier than might have been expected, that is, before the time point when the path movement of the disambiguating sign was visible. We suggest that in the visual modality, transitional movement of the articulators prior to the disambiguating verb position or co-occurring non-manual (face/body) markings were used in resolving the local ambiguity in ÖGS. Thus, whereas the processing strategy of "subject preference" is cross-modal at the linguistic level, the cues that enable the processor to apply that strategy differ in signing as compared to speech.

Academic Achievement of Deaf and Hard-of-Hearing Students in an ASL/English Bilingual Program

There has been a scarcity of studies exploring the influence of students' American Sign Language (ASL) proficiency on their academic achievement in ASL/English bilingual programs. The aim of this study was to determine the effects of ASL proficiency on reading comprehension skills and academic achievement of 85 deaf or hard-of-hearing signing students. Two subgroups, differing in ASL proficiency, were compared on the Northwest Evaluation Association Measures of Academic Progress and the reading comprehension subtest of the Stanford Achievement Test, 10th edition. Findings suggested that students highly proficient in ASL outperformed their less proficient peers in nationally standardized measures of reading comprehension, English language use, and mathematics. Moreover, a regression model consisting of 5 predictors including variables regarding education, hearing devices, and secondary disabilities as well as ASL proficiency and home language showed that ASL proficiency was the single variable significantly predicting results on all outcome measures. This study calls for a paradigm shift in thinking about deaf education by focusing on characteristics shared among successful deaf signing readers, specifically ASL fluency.

The Cognitive Neuroscience of Sign Language: Engaging Undergraduate Students' Critical Thinking Skills Using the Primary Literature

This article presents a modular activity on the neurobiology of sign language that engages undergraduate students in reading and analyzing the primary functional magnetic resonance imaging (fMRI) literature. Drawing on a seed empirical article and subsequently published critique and rebuttal, students are introduced to a scientific debate concerning the functional significance of right-hemisphere recruitment observed in some fMRI studies of sign language processing. The activity requires minimal background knowledge and is not designed to provide students with a specific conclusion regarding the debate. Instead, the activity and set of articles allow students to consider key issues in experimental design and analysis of the primary literature, including critical thinking regarding the cognitive subtractions used in blocked-design fMRI studies, as well as possible confounds in comparing results across different experimental tasks. By presenting articles representing different perspectives, each cogently argued by leading scientists, the readings and activity also model the type of debate and dialogue critical to science, but often invisible to undergraduate science students. Student self-report data indicate that undergraduates find the readings interesting and that the activity enhances their ability to read and interpret primary fMRI articles, including evaluating research design and considering alternate explanations of study results. As a stand-alone activity completed primarily in one 60-minute class block, the activity can be easily incorporated into existing courses, providing students with an introduction both to the analysis of empirical fMRI articles and to the role of debate and critique in the field of neuroscience.

Neuronal bases of structural coherence in contemporary dance observation

The neuronal processes underlying dance observation have been the focus of an increasing number of brain imaging studies over the past decade. However, the existing literature mainly dealt with effects of motor and visual expertise, whereas the neural and cognitive mechanisms that underlie the interpretation of dance choreographies remained unexplored. Hence, much attention has been given to the action observation network (AON) whereas the role of other potentially relevant neuro-cognitive mechanisms such as mentalizing (theory of mind) or language (narrative comprehension) in dance understanding is yet to be elucidated. We report the results of an fMRI study where the structural coherence of short contemporary dance choreographies was manipulated parametrically using the same taped movement material. Our participants were all trained dancers. The whole-brain analysis argues that the interpretation of structurally coherent dance phrases involves a subpart (superior parietal) of the AON as well as mentalizing regions in the dorsomedial prefrontal cortex. An ROI analysis based on a similar study using linguistic materials (Pallier et al., 2011) suggests that structural processing in language and dance might share certain neural mechanisms.

Functional connectivity in task-negative network of the Deaf: effects of sign language experience

Prior studies investigating cortical processing in Deaf signers suggest that life-long experience with sign language and/or auditory deprivation may alter the brain’s anatomical structure and the function of brain regions typically recruited for auditory processing (Emmorey et al., 2010; Pénicaud et al., 2013 inter alia). We report the first investigation of the task-negative network in Deaf signers and its functional connectivity—the temporal correlations among spatially remote neurophysiological events. We show that Deaf signers manifest increased functional connectivity between posterior cingulate/precuneus and left medial temporal gyrus (MTG), but also inferior parietal lobe and medial temporal gyrus in the right hemisphere- areas that have been found to show functional recruitment specifically during sign language processing. These findings suggest that the organization of the brain at the level of inter-network connectivity is likely affected by experience with processing visual language, although sensory deprivation could be another source of the difference. We hypothesize that connectivity alterations in the task negative network reflect predictive/automatized processing of the visual signal.