The scarce literature on the processing of internally headed relative clauses (IHRCs) seems to challenge the universality of the subject advantage (e.g., Lau & Tanaka [2021, Glossa: A Journal of General Linguistics, 6(1), 34], for spoken languages; Hauser et al. [2021, Glossa: A Journal of General Linguistics, 6(1), 72], for sign languages). In this study, we investigate the comprehension of subject and object IHRCs in Italian Sign Language (LIS) deaf native and non-native signers, and hearing LIS/Italian CODAs (children of deaf adults). We use the eye-tracking Visual-only World Paradigm (Hauser & Pozniak [2019, Poster presented at the AMLAP 2019 conference]) recording online and offline responses. Results show that a subject advantage is detected in the online and offline responses of CODAs and in the offline responses of deaf native signers. Results also reveal a higher rate of accuracy in CODAs' responses. We discuss the difference in performance between the two populations in the light of bilingualism-related cognitive advantages, and lack of proper educational training in Italian and LIS for the deaf population in Italy.

Bimodal bilinguals master languages in two modalities, spoken and signed, and can use them simultaneously due to the independence of the articulators. This behavior, named code-blending, is one of the hallmarks of bimodal bilingualism. Lexical experiments on production and comprehension in American Sign Language/English showed that blending is not cognitively costly and facilitates lexical access. In this work, we replicated the blending advantage in lexical comprehension for hearing bimodal bilinguals with two other language pairs, French Sign Language (LSF)–French and Italian Sign Language (LIS)–Italian, and we explored whether the facilitation is also found at the sentential level. Results show that blended utterances for languages with incongruent word order like LIS–Italian were processed slower than monolingual utterances, while no difference was found when the word orders were congruent (LSF–French). We discuss these findings in light of linguistic theories of syntactic structure derivation in bimodal bilinguals.

The present study provides insight into cross-language activation in hearing bimodal bilinguals by (1) examining co-activation of spoken words during processing of signs by hearing bimodal bilingual users of Dutch (their L1) and Sign Language of the Netherlands (NGT; late learners) and (2) investigating the contribution of mouthings to bimodal cross-language activation. NGT signs were presented with or without mouthings in two sign-picture verification experiments. In both experiments the phonological relation (unrelated, cohort overlap or final rhyme overlap) between the Dutch translation equivalents of the NGT signs and pictures was manipulated. Across both experiments, the results showed slower responses for sign-picture pairs with final rhyme overlap relative to phonologically unrelated sign-picture pairs, indicating co-activation of the spoken language during sign processing, but no significant effect for sign-picture pairs with cohort overlap in Dutch. In addition, co-activation was not affected by the presence or absence of mouthings.

To investigate cross-linguistic interactions in bimodal bilingual production, behavioural and electrophysiological measures (ERPs) were recorded from 24 deaf bimodal bilinguals while naming pictures in Catalan Sign Language (LSC). Two tasks were employed, a picture-word interference and a picture-picture interference task. Cross-linguistic effects were explored via distractors that were either semantically related to the target picture, to the phonology/orthography of the Spanish name of the target picture, or were unrelated. No semantic effects were observed in sign latencies, but ERPs differed between semantically related and unrelated distractors. For the form-related manipulation, a facilitation effect was observed both behaviourally and at the ERP level. Importantly, these effects were not influenced by the type of distractor (word/picture) presented providing the first piece of evidence that deaf bimodal bilinguals are sensitive to oral language in sign production. Implications for models of cross-linguistic interactions in bimodal bilinguals are discussed.

Previous work indicates that 1) adults with native sign language experience produce more manual co-speech gestures than monolingual non-signers, and 2) one year of ASL instruction increases gesture production in adults, but not enough to differentiate them from non-signers. To elucidate these effects, we asked early ASL–English bilinguals, fluent late second language (L2) signers (≥ 10 years of experience signing), and monolingual non-signers to retell a story depicted in cartoon clips to a monolingual partner. Early and L2 signers produced manual gestures at higher rates compared to non-signers, particularly iconic gestures, and used a greater variety of handshapes. These results indicate susceptibility of the co-speech gesture system to modification by extensive sign language experience, regardless of the age of acquisition. L2 signers produced more ASL signs and more handshape varieties than early signers, suggesting less separation between the ASL lexicon and the co-speech gesture system for L2 signers.

No previous research has investigated the neural correlates of vocabulary acquisition in second language learners of sign language. The present study investigated whether poor vocabulary knowledge engaged similar prefrontal lexico-semantic regions as seen in unimodal L2 learners. Behavioral improvements in vocabulary knowledge in a cohort of M2L2 learners were quantified. Results indicated that there is significant increase in vocabulary knowledge after one semester, but stabilized in the second semester. A longitudinal fMRI analysis was implemented for a subset of learners who were followed for the entire 10 months during initial sign language acquisition. The results indicated that learners who had poor sign vocabulary knowledge consistently showed greater activation in regions involved in motor simulation, salience, biological motion and spatial processing, and lexico-semantic retrieval. In conclusion, poor vocabulary knowledge requires greater engagement of modality-independent and modality-dependent regions, which could account for behavioral evidence of difficulty in visual phonology processing.

In language switching, it is assumed that in order to produce a response in one language, the other language must be inhibited. In unimodal (spoken-spoken) language switching, the fact that the languages share the same primary output channel (the mouth) means that only one language can be produced at a time. In bimodal (spoken-signed) language switching, however, it is possible to produce both languages simultaneously. In our study, we examined modality effects in language switching using multilingual subjects (speaking German, English, and German Sign Language). Focusing on German vocal responses, since they are directly compatible across conditions, we found shorter reaction times, lower error rates, and smaller switch costs in bimodal vs. unimodal switching. This result suggests that there are different inhibitory mechanisms at work in unimodal and bimodal language switching. We propose that lexical inhibition is involved in unimodal switching, whereas output channel inhibition is involved in bimodal switching.

Mouthings, the spoken language elements in sign language discourse, are typically analysed as having a redundant, one-on-one relationship with manual signs, both semantically and temporally. We explore exceptions to this presupposed semantic and temporal congruency in a corpus of spontaneous signed conversation by deaf users of Sign Language of the Netherlands (NGT). We identify specifying mouthings (words with a different meaning than the co-occurring sign), solo mouthings (uttered while the hands are inactive) and added mouthings (words added to a signing stream without their corresponding sign), and make a sentence-level analysis of their occurrences. These non-redundant mouthings occurred in 12% of all utterances, and were made by almost all signers. We argue for the presence of a code-blending continuum for NGT, where NGT is the matrix language and spoken Dutch is blended in, in various degrees. We suggest expansion of existing code-mixing models, to allow for description of bimodal mixing.

In this study we followed the characteristics and use of code-mixing by eight KODAs – hearing children of Deaf parents – from the age of 12 to 36 months. The children's interaction was video-recorded twice a year during three different play sessions: with their Deaf parent, with the Deaf parent and a hearing adult, and with the hearing adult alone. Additionally, data were collected on the children's overall language development in both sign language and spoken language. Our results showed that the children preferred to produce code-blends – simultaneous production of semantically congruent signs and words – in a way that was in accordance with the morphosyntactic structure of both languages being acquired. A Deaf parent as the interlocutor increased the number of and affected the type of code-blended utterances. These findings suggest that code-mixing in young bimodal bilingual KODA children can be highly systematic and synchronised in nature and can indicate pragmatic development.

Many bimodal bilinguals are immersed in a spoken language-dominant environment from an early age and, unlike unimodal bilinguals, do not necessarily divide their language use between languages. Nonetheless, early ASL–English bilinguals retrieved fewer words in a letter fluency task in their dominant language compared to monolingual English speakers with equal vocabulary level. This finding demonstrates that reduced vocabulary size and/or frequency of use cannot completely account for bilingual disadvantages in verbal fluency. Instead, retrieval difficulties likely reflect between-language interference. Furthermore, it suggests that the two languages of bilinguals compete for selection even when they are expressed with distinct articulators.

This study investigated the structure of the bimodal bilingual lexicon. In the cross-modal priming task nonnative sign language learners heard an English word (e.g., keys) and responded to the lexicality of a signed target: an underlying rhyme (e.g., cheese) or a sign neighbor of that word (e.g., paper). The results indicated that rhyme words were retrieved more quickly and the L2 neighbors were faster for beginner learners. An item analysis also indicated that semantics did not facilitate neighbor retrieval and high frequency signs were retrieved more quickly. The AX discrimination task showed that learners focus on handshape and movement parameters and discriminate equally. The interlanguage dynamics play an important role in which phonological parameters are used and the spread of activation over time. A nonselective, integrated model of the bimodal bilingual lexicon is proposed such that lateral connections are weakened over time and handshape parameter feeds most of the activation to neighboring signs as a function of system dynamics.

Bimodal bilinguals, fluent in a signed and a spoken language, exhibit a unique form of bilingualism because their two languages access distinct sensory-motor systems for comprehension and production. Differences between unimodal and bimodal bilinguals have implications for how the brain is organized to control, process, and represent two languages. Evidence from code-blending (simultaneous production of a word and a sign) indicates that the production system can access two lexical representations without cost, and the comprehension system must be able to simultaneously integrate lexical information from two languages. Further, evidence of cross-language activation in bimodal bilinguals indicates the necessity of links between languages at the lexical or semantic level. Finally, the bimodal bilingual brain differs from the unimodal bilingual brain with respect to the degree and extent of neural overlap for the two languages, with less overlap for bimodal bilinguals.

We used picture–word interference (PWI) to discover a) whether cross-language activation at the lexical level can yield phonological priming effects when languages do not share phonological representations, and b) whether semantic interference effects occur without articulatory competition. Bimodal bilinguals fluent in American Sign Language (ASL) and English named pictures in ASL while listening to distractor words that were 1) translation equivalents, 2) phonologically related to the target sign through translation, 3) semantically related, or 4) unrelated. Monolingual speakers named pictures in English. Production of ASL signs was facilitated by words that were phonologically related through translation and by translation equivalents, indicating that cross-language activation spreads from lexical to phonological levels for production. Semantic interference effects were not observed for bimodal bilinguals, providing some support for a post-lexical locus of semantic interference, but which we suggest may instead reflect time course differences in spoken and signed production in the PWI task.

To address the negative effects of deafness on spoken language acquisition, many clinicians suggest using cochlear implant (CI) and oral education and advise against sign language, even when combined with spoken language (i.e., bilingualism), believing that it may slow down spoken language development. In a deaf child with CI who was exposed at an early age to Italian Sign Language and spoken Italian, we evaluated language development and the relationship between the two languages. The number of words/signs produced by the child consistently increased with age, and the vocabulary growth rate in spoken Italian was equivalent to that of hearing peers. Before CI, the child relied almost exclusively on sign language; after CI, he gradually shifted to spoken Italian yet still used sign language when unable to retrieve words in spoken Italian. We conclude that bimodal bilingualism may scaffold the development of spoken language also in deaf children with CI.

This study examined temporal reference marking in texts written by Dutch deaf children and adults who differed in sign language proficiency. The temporal reference marking systems in Dutch and Sign Language of the Netherlands (SLN) differ substantially, with Dutch having a wide range of lexical and morphological markers of temporal reference, and SLN relying on lexical marking of temporal reference. The results showed that the youngest proficient signers had difficulties with tense morphology: they avoided the marked past tense form in narratives and omitted verbs, but showed no problems with lexical marking of temporal reference. In the older proficient signing writers, verb morphology emerged, and in proficient signing adults temporal reference marking resembled that of the hearing adults. This study shows that in order to gain more insight into deaf people's writing, it is important to adopt a bilingual perspective and take variations in sign language proficiency into account.