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The neurobiology of word and sign semantic processing in deaf adult signers: Evidence from N400 priming and language proficiency
Poster Session E, Friday, October 2, 11:00 am - 1:00 pm, Wangari Maathai
Zed Sehyr1, Erin Campbell2; 1Chapman University, 2Boston University
The N400 is an event‑related potential (ERP) component linked to semantic processing, characterized by a negative‑going waveform ~400 ms post-stimulus onset. N400 responses are typically larger for semantically unrelated than related word pairs and are interpreted as reflecting increased demands on semantic integration (Kutas & Hillyard, 1980). The N400 has played a central role in theories of how meaning is organized and processed in the brain. However, most N400 research is based on hearing individuals using spoken languages, leaving open the question of whether the neural mechanisms supporting semantic integration are language‑specific or reflect broader, modality‑independent processes operating across spoken, written, and signed languages. This study examined N400 responses to written English words in deaf adult ASL signers and hearing non‑signers, and N400 responses to ASL signs in deaf signers. We examined how neural responses across these tasks relate to individual differences in language and reading skill, and the extent to which semantic processing of words and signs is associated within individuals. Twenty-three deaf ASL signers and 27 hearing non‑signers completed an assessment battery measuring English spelling, vocabulary (Dunn& Dunn, 2007), reading fluency (Schrank et al., 2014), and non‑verbal reasoning (Kaufman & Kaufman, 2004). Deaf participants also completed an ASL comprehension assessment (VL2, Gallaudet University). Both groups completed a visual word‑pair judgment task (ERP‑CORE; Kappenman et al., 2021), where they judged whether pairs of words were semantically related or unrelated. Deaf participants also completed a sign‑pair judgment task, with two ASL signs presented sequentially and participants judged them for semantic relatedness. ASL signs were drawn from a semantic association dataset (Kezar et al., 2023), modeled by a deaf native signer, and matched in structure and timing to the word‑pair task. EEG was recorded from 32 scalp electrodes using an actiCHamp system and processed using EEGLAB and ERPLAB. The N400 effect was quantified as the mean amplitude difference between unrelated and related trials (300–500 ms post‑target onset for words; 400–700 ms for signs) over centroparietal electrodes. On the word‑pair task, both deaf and hearing participants showed robust N400 effects, with unrelated targets eliciting more negative responses than related targets. The N400 effect was larger in hearing participants than in deaf participants and was associated with English reading skill: larger N400 effects were correlated with higher spelling (r = -0.42, p = .004) and reading fluency (r = -0.38, p = .01) scores. On the sign‑pair task, deaf participants showed a clear, albeit delayed, N400-like response to semantic relatedness, congruent with prior work (Leonard et al., 2012), but sign‑evoked N400 magnitude was not associated with English language measures (ps > .05), suggesting that associations between N400 amplitude and language scores are language-specific. Notably, N400 effect sizes for words and signs were positively correlated. Results suggest that the magnitude of the N400 reflects language‑specific proficiency, while semantic integration engages modality‑independent neural mechanisms. By examining semantic processing across written and signed languages within the same individuals, we improve our understanding of how sensory experience and language proficiency shape the neurobiology of semantic processing.
Topic Areas: Meaning: Lexical Semantics, Signed Language and Gesture