Justyna Kotowicz (Pedagogical University in Cracow, Poland) : “Sign language and cognition in deaf and hearing native signers”

Abstract:

Sign languages are fully-fledged, natural languages used by Deaf communities all over the world (Klima & Bellugi, 1979). Since the 1960s (e.g. Stokoe, 1960), the complexity and the uniqueness of sign languages have been investigated in a growing body of studies. However, up to the present, it is not fully understood how experience of sign language is connected with the cognitive processes in Deaf and hearing signers. In order to shed some light on the topic, I conducted two types of research: 1. studies focused on language skills in  deaf native signers and 2. investigations of cognitive functions in Deaf and hearing native signers. All participants, both Deaf and hearing, of my previous research were native users of sign language who were immersed in the visual-spatial language from birth. 

The first type of research concerned language skills of deaf native signers who used two languages: Polish Sign Language (Polski Język Migowy, PJM) and written Polish. Firstly, we adapted the British Sign Language Receptive Skills Test, the first standardized test to determine sign language proficiency in children (Herman et al., 1999), into Polish Sign Language (PJM), a less researched sign language (Kotowicz et al., 2020). At that time no valid and reliable test was available to assess Polish Sign Language (PJM) skills in deaf children. Additionally, the PJM Receptive Skills Test scores predicted reading comprehension skills in native signers (school-aged children) supporting the hypothesis that language competences in sign language are of significant importance for reading abilities of Deaf students (Mayberry et al., 2011). Currently, we are conducting a study that aim to analyse the fMRI data of deaf adults, Polish Sign Language (PJM) users, who performed the semantic judgement task (SJT) in the scanner. The sentence-level reading process in deaf individuals who use Polish Sign Language were compared to hearing individuals in order to investigate “the plasticity of the reading system” (Emmorey & Lee, 2021). The preliminary results showed that Deaf individuals had different activation pattern than hearing individuals (e.g. Deaf readers exhibited greater activation in the right hemisphere in: the inferior frontal gyrus (IFG, pars triangularis), the inferior temporal gyrus (ITG) and the left hemisphere: in the inferior occipital gyrus (IOG) and in the inferior temporal gyrus (ITG)).

The second type of studies aimed to investigate cognitive processes in Deaf and hearing signers, precisely, I was interested in cognitive control that encompasses high-level processes necessary to obtain a chosen goal or to overcome new challenges; this ability to control thinking is crucial for learning or for social life (Hughes et al., 2004). In the first study, we found that deaf children of deaf parents with early exposure to sign language did not have cognitive control deficits in: cognitive flexibility, planning or working memory when compared to hearing peers on a variety of task-based assessments. Deaf parents are likely to provide good language input and supportive parental behavior for cognitive control development in their deaf children (Hall et al., 2018). Exposure to natural sign language from infancy may support higher cognitive functioning in deaf children (Hall, 2020). The goal of another two study was to investigate cognitive control in hearing individuals who are native signers, raised by Deaf parents. Experience of a sign language and a spoken language provides a unique opportunity to examine the cognitive effect of using two highly different languages with two distinct perceptual and motor systems (Emmorey et al., 2008). In one study we looked on cognitive control in hearing children (native signers) and in another one – in hearing adults (users of sign language). In both studies hearing native signers were compared to monolinguals and bilinguals using two spoken languages.  The results showed that hearing children did not significantly outperform other children, however, hearing adult (sign language users) had cognitive control advantage over monolinguals. Hence, we proposed that cognitive control skills may be connected with language switching opportunities and language processing demands and not only by simple usage of two highly different languages: sign language and spoken language (Anderson et al., 2018).