Poster E6, Saturday, August 18, 3:00 – 4:45 pm, Room 2000AB
Investigating brain lateralization during speechreading and reading in deaf adults using functional transcranial Doppler sonography (fTCD).
Eva Gutierrez-Sigut1,2, Victoria Mousley2, Laura Monroy2, Sophie Harte2, Mairead MacSweeney2;1University of Valencia, 2University College London
Among hearing people, the use of phonological information is strongly linked to reading ability. It has been proposed that as reading development progresses, the processing of words becomes increasingly left lateralized due to mapping of orthographic forms onto already left lateralized phonological representations of speech (e.g. Maurer and McCandliss, 2008). Consistent with this hypothesis, greater phonological awareness has been linked with stronger left lateralization for visual word processing (Sacchi & Laszlo, 2016). Furthermore, weaker language lateralization has often been linked to language disorders, including developmental dyslexia (see Bishop, 2013). Reading is a difficult task for most people born deaf (e.g. Conrad, 1979; Traxler, 2000). Knowledge about the phonological structure of words in deaf people is thought to be mainly based upon articulatory feedback from speech and visual information from lip patterns, (i.e. speechreading; Kyle et al., 2016). Support for this hypothesis would come from evidence of left-lateralisation for phonological skills in deaf adults which correlate with speech-related skills, such as speechreading. Here we use functional Transcranial Doppler sonography (fTCD), a reliable, easy, noninvasive and inexpensive way to establish hemispheric dominance during cognitive tasks (Deppe et al., 2004) to investigate lateralization in adult congenitally profoundly deaf participants (N=14) during a range of different on-line language tasks. We have previously validated these tasks in hearing readers. Specifically, we measured the laterality indices (LIs) during language generation (semantic fluency), on-line reading, speechreading of short stories and rhyme judgement tasks. We investigate the relationships between strength of lateralization for these tasks and performance during the tasks (accuracy) as well as standardized measures of reading and speechreading abilities. Results showed that deaf participants were predominantly left lateralized during the language generation task. This is the gold standard task to establish hemispheric lateralization. The strength of lateralization for the rhyme judgment task was lower but not significantly different from the generation task. Finally, significantly lower LIs were found for both the reading and speechreading tasks than for the generation task. Consistent with previous research with deaf people, behavioural scores on the speechreading test were positively correlated with accuracy during the rhyme judgement and reading tasks. The data suggest a gradation in strength of lateralization depending on the task. We discuss the patterns of lateralization in terms of the language demands of the different tasks (see Bradshaw et al., 2017).
Topic Area: Phonology and Phonological Working Memory