Restricted language access during childhood affects adult brain structure in selective language regions.

Due to the ubiquitous nature of language in the environment of infants, how it affects the anatomical structure of the brain language system over the lifespan is not well understood. In this study, we investigated the effects of early language experience on the adult brain by examining anatomical features of individuals born deaf with typical or restricted language experience in early childhood. Twenty-two deaf adults whose primary language was American Sign Language and were first immersed in it at ages ranging from birth to 14 y participated. The control group was 21 hearing non-signers. We acquired T1-weighted magnetic resonance images and used FreeSurfer [B. Fischl, Neuroimage 62, 774-781(2012)] to reconstruct the brain surface. Using an a priori regions of interest (ROI) approach, we identified 17 language and 19 somatomotor ROIs in each hemisphere from the Human Connectome Project parcellation map [M. F. Glasser et al., Nature 536, 171-178 (2016)]. Restricted language experience in early childhood was associated with negative changes in adjusted grey matter volume and/or cortical thickness in bilateral fronto-temporal regions. No evidence of anatomical differences was observed in any of these regions when deaf signers with infant sign language experience were compared with hearing speakers with infant spoken language experience, showing that the effects of early language experience on the brain language system are supramodal.

Impoverished language in early childhood affects the development of complex sentence structure.

The hypothesis that impoverished language experience affects complex sentence structure development around the end of early childhood was tested using a fully randomized, sentence-to-picture matching study in American Sign Language (ASL). The participants were ASL signers who had impoverished or typical access to language in early childhood. Deaf signers whose access to language was highly impoverished in early childhood (N = 11) primarily comprehended structures consisting of a single verb and argument (Subject or Object), agreeing verbs, and the spatial relation or path of semantic classifiers. They showed difficulty comprehending more complex sentence structures involving dual lexical arguments or multiple verbs. As predicted, participants with typical language access in early childhood, deaf native signers (N = 17) or hearing second-language learners (N = 10), comprehended the range of 12 ASL sentence structures, independent of the subjective iconicity or frequency of the stimulus lexical items, or length of ASL experience and performance on non-verbal cognitive tasks. The results show that language experience in early childhood is necessary for the development of complex syntax. RESEARCH HIGHLIGHTS: Previous research with deaf signers suggests an inflection point around the end of early childhood for sentence structure development. Deaf signers who experienced impoverished language until the age of 9 or older comprehend several basic sentence structures but few complex structures. Language experience in early childhood is necessary for the development of complex sentence structure.

The Cortical Organization of Syntactic Processing Is Supramodal: Evidence from American Sign Language.

Areas within the left-lateralized neural network for language have been found to be sensitive to syntactic complexity in spoken and written language. Previous research has revealed that these areas are active for sign language as well, but whether these areas are specifically responsive to syntactic complexity in sign language independent of lexical processing has yet to be found. To investigate the question, we used fMRI to neuroimage deaf native signers' comprehension of 180 sign strings in American Sign Language (ASL) with a picture-probe recognition task. The ASL strings were all six signs in length but varied at three levels of syntactic complexity: sign lists, two-word sentences, and complex sentences. Syntactic complexity significantly affected comprehension and memory, both behaviorally and neurally, by facilitating accuracy and response time on the picture-probe recognition task and eliciting a left lateralized activation response pattern in anterior and posterior superior temporal sulcus (aSTS and pSTS). Minimal or absent syntactic structure reduced picture-probe recognition and elicited activation in bilateral pSTS and occipital-temporal cortex. These results provide evidence from a sign language, ASL, that the combinatorial processing of anterior STS and pSTS is supramodal in nature. The results further suggest that the neurolinguistic processing of ASL is characterized by overlapping and separable neural systems for syntactic and lexical processing.

When event knowledge overrides word order in sentence comprehension: Learning a first language after childhood.

Limited language experience in childhood is common among deaf individuals, which prior research has shown to lead to low levels of language processing. Although basic structures such as word order have been found to be resilient to conditions of sparse language input in early life, whether they are robust to conditions of extreme language delay is unknown. The sentence comprehension strategies of post-childhood, first-language (L1) learners of American Sign Language (ASL) with at least 9 years of language experience were investigated, in comparison to two control groups of learners with full access to language from birth (deaf native signers and hearing L2 learners who were native English speakers). The results of a sentence-to-picture matching experiment show that event knowledge overrides word order for post-childhood L1 learners, regardless of the animacy of the subject, while both deaf native signers and hearing L2 signers consistently rely on word order to comprehend sentences. Language inaccessibility throughout early childhood impedes the acquisition of even basic word order. Similar to the strategies used by very young children prior to the development of basic sentence structure, post-childhood L1 learners rely more on context and event knowledge to comprehend sentences. Language experience during childhood is critical to the development of basic sentence structure.

Implicit causality biases and thematic roles in American Sign Language.

Implicit causality (IC) biases, the tendency of certain verbs to elicit re-mention of either the first-mentioned noun phrase (NP1) or the second-mentioned noun phrase (NP2) from the previous clause, are important in psycholinguistic research. Understanding IC verbs and the source of their biases in signed as well as spoken languages helps elucidate whether these phenomena are language general or specific to the spoken modality. As the first of its kind, this study investigates IC biases in American Sign Language (ASL) and provides IC bias norms for over 200 verbs, facilitating future psycholinguistic studies of ASL and comparisons of spoken versus signed languages. We investigated whether native ASL signers continued sentences with IC verbs (e.g., ASL equivalents of 'Lisa annoys Maya because…') by mentioning NP1 (i.e., Lisa) or NP2 (i.e., Maya). We found a tendency towards more NP2-biased verbs. Previous work has found that a verb's thematic roles predict bias direction: stimulus-experiencer verbs (e.g., 'annoy'), where the first argument is the stimulus (causing annoyance) and the second argument is the experiencer (experiencing annoyance), elicit more NP1 continuations. Verbs with experiencer-stimulus thematic roles (e.g., 'love') elicit more NP2 continuations. We probed whether the trend towards more NP2-biased verbs was related to an existing claim that stimulus-experiencer verbs do not exist in sign languages. We found that stimulus-experiencer structure, while permitted, is infrequent, impacting the IC bias distribution in ASL. Nevertheless, thematic roles predict IC bias in ASL, suggesting that the thematic role-IC bias relationship is stable across languages as well as modalities.

Acquiring a first language in adolescence: the case of basic word order in American Sign Language.

Previous studies suggest that age of acquisition affects the outcomes of learning, especially at the morphosyntactic level. Unknown is how syntactic development is affected by increased cognitive maturity and delayed language onset. The current paper studied the early syntactic development of adolescent first language learners by examining word order patterns in American Sign Language (ASL). ASL uses a basic Subject-Verb-Object order, but also employs multiple word order variations. Child learners produce variable word order at the initial stage of acquisition, but later primarily produce canonical word order. We asked whether adolescent first language learners acquire ASL word order in a fashion parallel to child learners. We analyzed word order preference in spontaneous language samples from four adolescent L1 learners collected longitudinally from 12 months to six years of ASL exposure. Our results suggest that adolescent L1 learners go through stages similar to child native learners, although this process also appears to be prolonged.

Neural Language Processing in Adolescent First-Language Learners: Longitudinal Case Studies in American Sign Language.

One key question in neurolinguistics is the extent to which the neural processing system for language requires linguistic experience during early life to develop fully. We conducted a longitudinal anatomically constrained magnetoencephalography (aMEG) analysis of lexico-semantic processing in 2 deaf adolescents who had no sustained language input until 14 years of age, when they became fully immersed in American Sign Language. After 2 to 3 years of language, the adolescents' neural responses to signed words were highly atypical, localizing mainly to right dorsal frontoparietal regions and often responding more strongly to semantically primed words (Ferjan Ramirez N, Leonard MK, Torres C, Hatrak M, Halgren E, Mayberry RI. 2014. Neural language processing in adolescent first-language learners. Cereb Cortex. 24 (10): 2772-2783). Here, we show that after an additional 15 months of language experience, the adolescents' neural responses remained atypical in terms of polarity. While their responses to less familiar signed words still showed atypical localization patterns, the localization of responses to highly familiar signed words became more concentrated in the left perisylvian language network. Our findings suggest that the timing of language experience affects the organization of neural language processing; however, even in adolescence, language representation in the human brain continues to evolve with experience.

Acceptability judgments still matter: Deafness and documentation.

The target article's call to end reliance on acceptability judgments is premature. First, it restricts syntactic inquiry to cases were a semantically equivalent alternative is available. Second, priming studies require groups of participants who are linguistically homogenous and whose grammar is known to the researcher. These requirements would eliminate two major research areas: syntactic competence in d/Deaf individuals, and language documentation. (We follow the convention of using deaf to describe hearing levels, Deaf to describe cultural identity, and d/Deaf to include both. Our own work has focused on Deaf signers, but the same concerns could apply to other deaf populations.).

Who's on First? Investigating the referential hierarchy in simple native ASL narratives.

Discussions of reference tracking in spoken languages often invoke some version of a referential hierarchy. In this paper, we asked whether this hierarchy applies equally well to reference tracking in a visual language, American Sign Language, or whether modality differences influence its structure. Expanding the results of previous studies, this study looked at ASL referential devices beyond nouns, pronouns, and zero anaphora. We elicited four simple narratives from eight native ASL signers, and examined how the signers tracked reference throughout their stories. We found that ASL signers follow general principles of the referential hierarchy proposed for spoken languages by using nouns for referent introductions, and zero anaphora for referent maintenance. However, we also found significant differences such as the absence of pronouns in the narratives, despite their existence in ASL, and differential use of verbal and constructed action zero anaphora. Moreover, we found that native signers' use of classifiers varied with discourse status in a way that deviated from our expectations derived from the referential hierarchy for spoken languages. On this basis, we propose a tentative hierarchy of referential expressions for ASL that incorporates modality specific referential devices.

Neural language processing in adolescent first-language learners.

The relation between the timing of language input and development of neural organization for language processing in adulthood has been difficult to tease apart because language is ubiquitous in the environment of nearly all infants. However, within the congenitally deaf population are individuals who do not experience language until after early childhood. Here, we investigated the neural underpinnings of American Sign Language (ASL) in 2 adolescents who had no sustained language input until they were approximately 14 years old. Using anatomically constrained magnetoencephalography, we found that recently learned signed words mainly activated right superior parietal, anterior occipital, and dorsolateral prefrontal areas in these 2 individuals. This spatiotemporal activity pattern was significantly different from the left fronto-temporal pattern observed in young deaf adults who acquired ASL from birth, and from that of hearing young adults learning ASL as a second language for a similar length of time as the cases. These results provide direct evidence that the timing of language experience over human development affects the organization of neural language processing.

Subjective frequency ratings for 432 ASL signs.

Given the importance of lexical frequency for psycholinguistic research and the lack of comprehensive frequency data for sign languages, we collected subjective estimates of lexical frequency for 432 signs in American Sign Language (ASL). Our participants were 59 deaf signers who first began to acquire ASL at ages ranging from birth to 14 years old and who had a minimum of 10 years of experience. Subjective frequency estimates were made on a scale ranging from 1 = rarely see the sign to 7 = always see the sign. The mean subjective frequency ratings for individual signs did not vary in relation to age of sign language exposure (AoLE), chronological age, or length of ASL experience. Nor did AoLE show significant effects on the response times (RTs) for making the ratings. However, RTs were highly correlated with mean frequency ratings. These results suggest that the distributions of subjective lexical frequencies are consistent across signers with varying AoLEs. The implications for research practice are that subjective frequency ratings from random samples of highly experienced deaf signers can provide a reasonable measure of lexical control in sign language experiments. The Appendix gives the mean and median subjective frequency ratings and the mean and median log(RT) of the ASL signs for the entire sample; the supplemental material gives these measures for the three AoLE groups: native, early, and late.

Signed words in the congenitally deaf evoke typical late lexicosemantic responses with no early visual responses in left superior temporal cortex.

Congenitally deaf individuals receive little or no auditory input, and when raised by deaf parents, they acquire sign as their native and primary language. We asked two questions regarding how the deaf brain in humans adapts to sensory deprivation: (1) is meaning extracted and integrated from signs using the same classical left hemisphere frontotemporal network used for speech in hearing individuals, and (2) in deafness, is superior temporal cortex encompassing primary and secondary auditory regions reorganized to receive and process visual sensory information at short latencies? Using MEG constrained by individual cortical anatomy obtained with MRI, we examined an early time window associated with sensory processing and a late time window associated with lexicosemantic integration. We found that sign in deaf individuals and speech in hearing individuals activate a highly similar left frontotemporal network (including superior temporal regions surrounding auditory cortex) during lexicosemantic processing, but only speech in hearing individuals activates auditory regions during sensory processing. Thus, neural systems dedicated to processing high-level linguistic information are used for processing language regardless of modality or hearing status, and we do not find evidence for rewiring of afferent connections from visual systems to auditory cortex.

Structural brain changes linked to delayed first language acquisition in congenitally deaf individuals.

Early language experience is essential for the development of a high level of linguistic proficiency in adulthood and in a recent functional Magnetic Resonance Imaging (fMRI) experiment, we showed that a delayed acquisition of a first language results in changes in the functional organization of the adult brain (Mayberry et al., 2011). The present study extends the question to explore if delayed acquisition of a first language also modulates the structural development of the brain. To this end, we carried out anatomical MRI in the same group of congenitally deaf individuals who varied in the age of acquisition of a first language, American Sign Language -ASL (Mayberry et al., 2011) and used a neuroanatomical technique, Voxel-Based Morphometry (VBM), to explore changes in gray and white matter concentrations across the brain related to the age of first language acquisition. The results show that delayed acquisition of a first language is associated with changes in tissue concentration in the occipital cortex close to the area that has been found to show functional recruitment during language processing in these deaf individuals with a late age of acquisition. These findings suggest that a lack of early language experience affects not only the functional but also the anatomical organization of the brain.

Sign language aphasia from a neurodegenerative disease.

While Alois Alzheimer recognized the effects of the disease he described on speech and language in his original description of the disease in 1907, the effects of Alzheimer's disease (AD) on language in deaf signers has not previously been reported. We evaluated a 55-year-old right-handed congenitally deaf woman with a 2-year history of progressive memory loss and a deterioration of her ability to communicate in American Sign Language, which she learned at the age of eight. Examination revealed that she had impaired episodic memory as well as marked impairments in the production and comprehension of fingerspelling and grammatically complex sentences. She also had signs of anomia as well as an ideomotor apraxia and visual-spatial dysfunction. This report illustrates the challenges in evaluation of a patient for the presence of degenerative dementia when the person is deaf from birth, uses sign language, and has a late age of primary language acquisition. Although our patient could neither speak nor hear, in many respects her cognitive disorders mirror those of patients with AD who had normally learned to speak.

Skilled deaf readers have an enhanced perceptual span in reading.

Recent evidence suggests that, compared with hearing people, deaf people have enhanced visual attention to simple stimuli viewed in the parafovea and periphery. Although a large part of reading involves processing the fixated words in foveal vision, readers also utilize information in parafoveal vision to preprocess upcoming words and decide where to look next. In the study reported here, we investigated whether auditory deprivation affects low-level visual processing during reading by comparing the perceptual span of deaf signers who were skilled and less-skilled readers with the perceptual span of skilled hearing readers. Compared with hearing readers, the two groups of deaf readers had a larger perceptual span than would be expected given their reading ability. These results provide the first evidence that deaf readers' enhanced attentional allocation to the parafovea is used during complex cognitive tasks, such as reading.

Pronoun Production and Comprehension in American Sign Language: The Interaction of Space, Grammar, and Semantics.

Spoken language research has investigated how pronouns are influenced by grammar and semantics/pragmatics. In contrast, sign language research has focused on unambiguous pronominal reference arising from spatial co-reference. However, understanding signed pronouns contributes to cross-linguistically valid models of pronoun production and comprehension. In two sentence-continuation experiments, the present study investigated how linguistic use of space (modality-specific), antecedent grammatical role and verb implicit causality bias (modality-independent) affect American Sign Language (ASL) pronouns. Production of pronouns was determined by antecedent grammatical role, and overt pronouns were marginally more frequent for referents articulated in specific areas of signing space compared to neutral space. Signers interpreted pronouns using spatial information and, notably, verb bias, despite spatial co-reference supposedly removing the ambiguity that verb bias resolves. These findings demonstrate that ASL pronouns are subject to modality-independent factors, despite their use of space, and lend support to models of pronominal reference positing a production/comprehension asymmetry.

Reading achievement in relation to phonological coding and awareness in deaf readers: a meta-analysis.

The relation between reading ability and phonological coding and awareness (PCA) skills in individuals who are severely and profoundly deaf was investigated with a meta-analysis. From an initial set of 230 relevant publications, 57 studies were analyzed that experimentally tested PCA skills in 2,078 deaf participants. Half of the studies found statistically significant evidence for PCA skills and half did not. A subset of 25 studies also tested reading proficiency and showed a wide range of effect sizes. Overall PCA skills predicted 11% of the variance in reading proficiency in the deaf participants. Other possible modulating factors, such as task type and reading grade level, did not explain the remaining variance. In 7 studies where it was measured, language ability predicted 35% of the variance in reading proficiency. These meta-analytic results indicate that PCA skills are a low to moderate predictor of reading achievement in deaf individuals and that other factors, most notably language ability, have a greater influence on reading development, as has been found to be the case in the hearing population.

Numeral Incorporation in Russian Sign Language: Phonological Constraints on Simultaneous Morphology.

This paper looks at numeral incorporation in Russian Sign Language (RSL). Numeral incorporation is the simultaneous combination of a numeral and a base sign into one sign. Incorporating forms typically use the numerical handshape combined simultaneously with the movement, location, and orientation of the base lexical sign; for example, "three months" will be expressed through an incorporating form 3_month. RSL is a language with a two-handed numeral system. Investigating two-handed numeral incorporation in RSL provides important insights into the constraints on numeral incorporation across languages as well as into the phonological structure of RSL. Numeral incorporation is a general preference in RSL that is highly constrained: not all calendric terms can incorporate, and not all numbers can be incorporated. For example, the sign month incorporates numbers one through nine (one through five are one-handed, and six through nine are two-handed). The incorporating one-handed form 5_minute exists, while the two-handed *6_minute form does not occur (that is, its meaning is expressed sequentially), and the sign day does not incorporate numbers at all. These limits are conditioned for semantic (lexical frequency, pragmatics) and phonological reasons. Because the numeral system of RSL is two-handed, the results show, first, that numeral incorporation is not limited to one-handed numerals. In addition, the results indicate that limits on numeral incorporation are not universal across sign languages. In RSL, each paradigm shows specific numeral incorporation limits that are phonologically conditioned. These limits are explained by the interaction of phonological rules at all levels of sign sublexical features for both the numeral and lexical sign: location, orientation, handshape, and movement. The location and orientation parameters of sign, however, have not been previously noted as being factors that limit numeral incorporation and sign complexity in a sign language. Our analyses, from both the numeral incorporation data and from elicitation and RSL corpus data, show that location and orientation function as phonological constraints in the composition of two-handed signs. Specifically, location and orientation operate in handshape symmetry restrictions. Our analyses also show that signs located on the head do not allow two-handed numeral incorporation. The corpus analyses corroborated this finding: all two-handed signs on the head that we found in our RSL corpus were symmetrical and frequently included weak drop, such that we found no asymmetrical two-handed signs on the head. Another symmetry restriction relates to orientation. Analyses of the RSL numeral incorporation data and the RSL corpus data and dictionaries show that RSL disprefers asymmetrical handshapes in two-handed signs having lateral orientation (palm facing the central line) (Fenlon et al. 2013).

Reference tracking in early stages of different modality L2 acquisition: Limited over-explicitness in novice ASL signers' referring expressions.

Previous research on reference tracking has revealed a tendency towards over-explicitness in second language (L2) learners. Only limited evidence exists that this trend extends to situations where the learner's first and second languages do not share a sensory-motor modality. Using a story-telling paradigm, this study examined how hearing novice L2 learners accomplish reference tracking in American Sign Language (ASL), and whether they transfer strategies from gesture. Our results revealed limited evidence of over-explicitness. Instead there was an overall similarity in the L2 learners' reference tracking to that of a native signer control group, even in the use of lexical nominals, pronouns and zero anaphora - areas where research on spoken L2 reference tracking predicts differences. Our data also revealed, however, that L2 learners have problems with the referential value of ASL classifiers, and with target-like use of zero anaphora from different verb types, as well as spatial modification. This suggests that over-explicitness occurs in the early stages of different modality L2 acquisition to a limited extent. We found no evidence of gestural transfer. Finally, we found that L2 learners reintroduce more than native signers, which could indicate that they, unlike native signers are not yet capable of utilizing the affordances of the visual modality to reference multiple entities simultaneously.

Effects of Early Language Deprivation on Brain Connectivity: Language Pathways in Deaf Native and Late First-Language Learners of American Sign Language.

Previous research has identified ventral and dorsal white matter tracts as being crucial for language processing; their maturation correlates with increased language processing capacity. Unknown is whether the growth or maintenance of these language-relevant pathways is shaped by language experience in early life. To investigate the effects of early language deprivation and the sensory-motor modality of language on white matter tracts, we examined the white matter connectivity of language-relevant pathways in congenitally deaf people with or without early access to language. We acquired diffusion tensor imaging (DTI) data from two groups of individuals who experienced language from birth, twelve deaf native signers of American Sign Language, and twelve hearing L2 signers of ASL (native English speakers), and from three, well-studied individual cases who experienced minimal language during childhood. The results indicate that the sensory-motor modality of early language experience does not affect the white matter microstructure between crucial language regions. Both groups with early language experience, deaf and hearing, show leftward laterality in the two language-related tracts. However, all three cases with early language deprivation showed altered white matter microstructure, especially in the left dorsal arcuate fasciculus (AF) pathway.