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

Development, Reliability, and Concurrent Validity of the American Sign Language Version of the Computerized Revised Token Test

PURPOSE

The present study assessed the test-retest reliability of the American Sign Language (ASL) version of the Computerized Revised Token Test (CRTT-ASL) and compared the differences and similarities between ASL and English reading by Deaf and hearing users of ASL.

METHOD

Creation of the CRTT-ASL involved filming, editing, and validating CRTT instructions, sentence commands, and scoring. Deaf proficient (DP), hearing nonproficient (HNP), and hearing proficient sign language users completed the CRTT-ASL and the English self-paced, word-by-word reading CRTT (CRTT-Reading-Word Fade [CRTT-R-wf]). Both tests were administered twice, 7-14 days apart, to assess test-retest reliability.

RESULTS

Preliminary findings suggested that the CRTT-ASL was acceptably reliable for the DP group across CRTT metrics. All groups showed adequate test-retest reliability for the CRTT-R-wf. The DP group scored comparably across the two language conditions, and on average, the DP group produced significantly lower scores than the two hearing groups on the CRTT-R-wf. The hearing groups did not differ significantly from each other on the CRTT-R-wf.

CONCLUSIONS

The CRTT-ASL may be reliable for assessing Deaf ASL users, the target population for its use. These findings serve as preliminary support for clinical and research use of the novel CRTT-ASL to assess language processing in Deaf individuals who use ASL. The CRTT-ASL may be sensitive to lexical processing inefficiencies in the Deaf signing population.

SUPPLEMENTAL MATERIAL

https://doi.org/10.23641/asha.28216259.

Assessing sign language comprehension in adults with intellectual disability and deafness

Language comprehension is an essential component of human development that is associated not only with expressive language development and knowledge acquisition, but also with social inclusion, mental health, and quality of life. For deaf and hard-of-hearing adults with intellectual disability, there is a paucity of measures of receptive sign language skills, although these are a prerequisite for individualized planning and evaluation of intervention. Assessments require materials and procedures that are accurate, feasible, and suitable for low levels of functioning. We adapted measures of English-language comprehension in young children-a direct assessment and a caregiver questionnaire-into Austrian Sign Language and to the target group of adults with intellectual disability and used them with a non-preselected sample of 67 deaf and hard-of-hearing adults with intellectual disability living in therapeutic communities specifically for deaf and hard-of-hearing people with multiple disabilities in Austria. Findings for both assessments demonstrate their construct validity, excellent internal consistency, and a large symmetrical distribution over the referential age range. Acceptance by the deaf and hard-of-hearing individuals and the caregivers and time-efficient administration suggest high practicability. We recommend further implementation in clinical practice, albeit with cautious interpretation of the results, and the inclusion of the instruments in research on intellectual disability and deafness.

Production of real signs but not pseudosigns affected by age of acquisition in American Sign Language

Research shows that insufficient language access in early childhood significantly affects language processing. While the majority of this work focuses on syntax, phonology also appears to be affected, though it is unclear exactly how. Here we investigated phonological production across age of acquisition of American Sign Language (ASL). Participants were deaf adult signers who first learned ASL at ages ranging from birth to 14 years and they performed both lexical decisions and repetitions of ASL signs and pseudosigns. Because phonological production has been understudied across age of acquisition, we were particularly interested in production accuracy for the sublexical phonological parameters of handshape, movement, and location. Lexical decision responses were slower and more accurate for impossible pseudosigns compared with possible pseudosigns, indicating participants were sensitive to ASL phonological structure regardless of age of acquisition. Despite this, age of acquisition affected repetition accuracy. Handshape errors were highest for those with earlier ages of acquisition, but movement errors were highest for those with later ages of acquisition, though this effect of age of acquisition was only seen for real ASL signs and not pseudosigns. The parameter error pattern for pseudosigns was not affected by age of acquisition. These results indicate that later age of acquisition does not inhibit the ability to produce ASL phonology but ultimately alters the processing of the phonological parameters when meaning and phonology are integrated.

Effect of sign language learning on temporal resolution of visual attention

The visual environment of sign language users is markedly distinct in its spatiotemporal parameters compared to that of non-signers. Although the importance of temporal and spectral resolution in the auditory modality for language development is well established, the spectrotemporal parameters of visual attention necessary for sign language comprehension remain less understood. This study investigates visual temporal resolution in learners of American Sign Language (ASL) at various stages of acquisition to determine how experience with sign language affects perceptual sampling. Using a flicker paradigm, we assessed the accuracy of identifying out-of-phase visual flicker objects at frequencies up to 60 Hz. Our findings reveal that third-semester ASL learners show increased accuracy in detecting high-frequency flicker, indicating enhanced temporal resolution. Interestingly, as learners achieve higher proficiency in ASL, their perceptual sampling reverts to typical levels, likely because of a shift toward predictive processing mechanisms in sign language comprehension. These results suggest that the temporal resolution of visual attention is malleable and can be influenced by the process of learning a visual language.

Bimodal aphasia and dysgraphia: Phonological output buffer aphasia and orthographic output buffer dysgraphia in spoken and sign language

We report a case of crossmodal bilingual aphasia-aphasia in two modalities, spoken and sign language-and dysgraphia in both writing and fingerspelling. The patient, Sunny, was a 42 year-old woman after a left temporo-parietal stroke, a speaker of Hebrew, Romanian, and English and an adult learner, daily user of Israeli Sign language (ISL). We assessed Sunny's spoken and sign languages using a comprehensive test battery of naming, reading, and repetition tasks, and also analysed her spontaneous-speech and sign. Her writing and fingerspelling were assessed using tasks of dictation, naming, and delayed copying. In spoken language production, Sunny showed a classical phonological output buffer (POB) impairment in naming, reading, repetition, and spontaneous production, with phonological errors (transpositions, substitutions, insertions, and omissions) in words and pseudo-words, and whole-unit errors in morphological affixes, function-words, and number-words, with a length effect. Importantly, her error pattern in ISL was remarkably similar in the parallel tasks, with phonological errors in signs and pseudo-signs, affecting all the phonological parameters of the sign (movement, handshape, location, and orientation), and whole-unit errors in morphemes, function-signs, and number-signs. Sunny's impairment was selective to the POB, without phonological input, semantic-conceptual, or syntactic deficits. This shows for the first time how POB impairment, a kind of conduction aphasia, manifests itself in a sign language, and indicates that the POB for sign-language has the same cognitive architecture as the one for spoken language. It may also indicate similar neural underpinnings for spoken and sign languages. In writing, Sunny forms the first case of a selective type of dysgraphia in fingerspelling, orthographic (graphemic) output buffer dysgraphia. In both writing and fingerspelling, she made letter errors (letter transpositions, substitutions, insertions, and omissions), as well as morphological errors and errors in function words, and showed length effect. Sunny's impairment was selective to the orthographic output buffer, whereas her reading, including orthographic input processing, was intact. This suggests that the orthographic output buffer is shared for writing and fingerspelling, at least in a late learner of sign language. The results shed further light on the architecture of phonological and orthographic production.

Argument ordering in simple sentences is affected by age of first language acquisition: Evidence from late first language signers of ASL

Research on the language acquisition of deaf individuals who are exposed to accessible linguistic input at a variety of ages has provided evidence for a sensitive period of first language acquisition. Recent studies have shown that deaf individuals who first learn language after early childhood, late first-language learners (LL1), do not comprehend reversible Subject-Verb-Object (SVO) sentences. The present study analyzed 478 signed productions elicited with pictures depicting simple events with one or two arguments by 28 signers. The argument order patterns of native signers converged with one another and the word order patterns of American Sign Language (ASL). By contrast, the ordering patterns of the LL1 signers did not converge with one another or with the patterns of the native signers. This indicates that early childhood is a period of heightened sensitivity to basic word order and may help explain why complex structures are difficult for LL1 signers to learn.

Individual differences in the neural dynamics of visual narrative comprehension: The effects of proficiency and age of acquisition

Understanding visual narrative sequences, as found in comics, is known to recruit similar cognitive mechanisms to verbal language. As measured by event-related potentials (ERPs), these manifest as initial negativities (N400, LAN) and subsequent positivities (P600). While these components are thought to index discrete processing stages, they differentially arise across participants for any given stimulus. In language contexts, proficiency modulates brain responses, with smaller N400 effects and larger P600 effects appearing with increasing proficiency. In visual narratives, recent work has also emphasized the role of proficiency in neural response patterns. We thus explored whether individual differences in proficiency modulate neural responses to visual narrative sequencing in similar ways as in language. We combined ERP data from 12 studies examining semantic and/or grammatical processing of visual narrative sequences. Using linear mixed effects modeling, we demonstrate differential effects of visual language proficiency and "age of acquisition" on N400 and P600 responses. Our results align with those reported in language contexts, providing further evidence for the similarity of linguistic and visual narrative processing, and emphasize the role of both proficiency and age of acquisition in visual narrative comprehension.

Predictive Processing in Sign Languages: A Systematic Review

The objective of this article was to review existing research to assess the evidence for predictive processing (PP) in sign language, the conditions under which it occurs, and the effects of language mastery (sign language as a first language, sign language as a second language, bimodal bilingualism) on the neural bases of PP. This review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) framework. We searched peer-reviewed electronic databases (SCOPUS, Web of Science, PubMed, ScienceDirect, and EBSCO host) and gray literature (dissertations in ProQuest). We also searched the reference lists of records selected for the review and forward citations to identify all relevant publications. We searched for records based on five criteria (original work, peer-reviewed, published in English, research topic related to PP or neural entrainment, and human sign language processing). To reduce the risk of bias, the remaining two authors with expertise in sign language processing and a variety of research methods reviewed the results. Disagreements were resolved through extensive discussion. In the final review, 7 records were included, of which 5 were published articles and 2 were dissertations. The reviewed records provide evidence for PP in signing populations, although the underlying mechanism in the visual modality is not clear. The reviewed studies addressed the motor simulation proposals, neural basis of PP, as well as the development of PP. All studies used dynamic sign stimuli. Most of the studies focused on semantic prediction. The question of the mechanism for the interaction between one’s sign language competence (L1 vs. L2 vs. bimodal bilingual) and PP in the manual-visual modality remains unclear, primarily due to the scarcity of participants with varying degrees of language dominance. There is a paucity of evidence for PP in sign languages, especially for frequency-based, phonetic (articulatory), and syntactic prediction. However, studies published to date indicate that Deaf native/native-like L1 signers predict linguistic information during sign language processing, suggesting that PP is an amodal property of language processing.

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.

Acquisition of Sign Languages

Natural sign languages of deaf communities are acquired on the same time scale as that of spoken languages if children have access to fluent signers providing input from birth. Infants are sensitive to linguistic information provided visually, and early milestones show many parallels. The modality may affect various areas of language acquisition; such effects include the form of signs (sign phonology), the potential advantage presented by visual iconicity, and the use of spatial locations to represent referents, locations, and movement events. Unfortunately, the vast majority of deaf children do not receive accessible linguistic input in infancy, and these children experience language deprivation. Negative effects on language are observed when first-language acquisition is delayed. For those who eventually begin to learn a sign language, earlier input is associated with better language and academic outcomes. Further research is especially needed with a broader diversity of participants.

Sensitive periods in cortical specialization for language: insights from studies with Deaf and blind individuals

Studies with Deaf and blind individuals demonstrate that linguistic and sensory experiences during sensitive periods have potent effects on neurocognitive basis of language. Native users of sign and spoken languages recruit similar fronto-temporal systems during language processing. By contrast, delays in sign language access impact proficiency and the neural basis of language. Analogously, early but not late-onset blindness modifies the neural basis of language. People born blind recruit 'visual' areas during language processing, show reduced left-lateralization of language and enhanced performance on some language tasks. Sensitive period plasticity in and outside fronto-temporal language systems shapes the neural basis of language.