Sign language processing and reading comprehension in deaf and hard-of-hearing individuals : evidence from event-related potentials and behavioural studies

Abstract

Deaf and hard-of-hearing (DHH) individuals comprise a special bilingual group of people that use sign language for daily communication and are expected to become good readers. However, it remains unclear how deaf signers perceive sign language. Also, there is no consensus regarding the heterogeneous nature of reading profiles among DHH students and the association of these profiles with language and cognitive skills. Therefore, the present thesis had a threefold aim: (1) to explore the time course of lexical sign processing; (2) to classify the heterogeneous reading profiles of DHH students and investigate their association with phonological and cognitive skills; (3) to identify unexpected poor comprehenders among the DHH population and understand the association between poor comprehension and language and cognitive deficits.

Study 1 examined automatic lexical sign processing in users of Hong Kong Sign Language. Using a visual oddball paradigm, deaf adult signers and hearing non-signers were presented with a sequence of lexical signs and non-signs in static images. When compared with hearing non-signers, deaf signers exhibited an enhanced vMMN that was elicited by the lexical signs at approximately 230 ms. Moreover, relative to the hearing non-signers, the deaf signers showed a larger P1-N170 complex evoked by both lexical sign and non-sign standards in the early time window between 65 ms and 170 ms. These findings underscore the presence of implicit lexical sign processing in deaf signers and that neural response difference between deaf signers and hearing non-signers occurs at the early stage of sign processing.

Study 2 identified the heterogeneous reading profiles of DHH students and examined the relationship between reading profiles and phonological and cognitive skills. Specifically, 146 DHH students aged 9-22 years underwent measurements of nonverbal intelligence, working memory, executive function, phonological skills, vocabulary, sight word reading, sign language comprehension, and text reading comprehension. We first categorized students based on their sight word reading and text reading comprehension, while the second categorization focused on the diversity of sign language comprehension and text reading comprehension. The results showed that segmental and suprasegmental phonological awareness and executive function skills distinguished poor profiles from good profiles for both types of categorization. These findings demonstrate the heterogeneous reading profile for DHH population and emphasize the relative importance of phonological and cognitive skills for different reading profiles.

Study 3 aimed to understand the unexpected poor comprehender profile of DHH students. Using a rigorous regression approach, 19 unexpected poor comprehenders, 24 expected average comprehenders, and 16 unexpected good comprehenders were identified. Compared with the expected average comprehenders, the unexpected poor comprehenders performed worse in sign language comprehension and segmental and suprasegmental phonological awareness but not in working memory and executive function. These findings underline the importance of language skills in text reading comprehension, suggesting that broad language deficits in DHH students may serve as precursors of their reading comprehension difficulties.

Taken together, this thesis reveals the automatic lexical sign processing and heterogeneous reading profiles of DHH students and further emphasizes that language and cognitive skills are crucial in differentiating their reading profiles.