The Neural Signature of Reading in Deaf Individuals

1. The Neural Signature of Reading in Deaf Individuals Daniel Koo, Joe Maisog, Carol LaSasso, Kelly Crain, Guinevere Eden Center for the Study of Learning Department of Pediatrics, Georgetown University Department of Hearing, Speech and Language Sciences, Gallaudet University

2. Outline Introduction • Deaf populations • Communication systems • Reading in Deaf populations Functional neuroanatomy of reading in deaf and hearing populations • ASL • English

3. Introduction to Deaf Populations • Approximately 28 million Americans have some degree of hearing loss • Approximately 600,000 to 1 million are “functionally deaf” • Acquired or congenital deafness before the age of 2 has significant implications for language development • Communication options: • American Sign Language • Cued Speech • Oral communication Sources: National Institute on Deafness and Other Communication Disorders, Gallaudet Research Institute, National Center for Health Statistics

4. American Sign Language (ASL) • Complete and Independent Language • Distinct Phonology, Morphology, Syntax • No relationship to English • Visuo-spatial Language • No writing system • Fingerspelling as sign-to-orthography correspondence?

5. Cued Speech • A visual/manual system based on the phonemic units of spoken language • Developed at Gallaudet College in 1966 by Dr. R. Orin Cornett • Designed to disambiguate and supplement information seen through lip-reading alone • Uses handshapes and hand placements near the face to visually represent phonemes

6. Cued Speech

7. ASL and Cued Speech

8. Reading in Deaf Populations 3rd to 4th grade reading achievement levels (Trybus & Karchmer, 1977; Allen, 1986; Traxler, 2000) Deaf Signers Variable reading proficiency but good readers show evidence of phonological influence in rhymed words (Hanson & Fowler, 1987; Hanson & McGarr, 1989) Deaf Cuers Skilled readers who show strong phonological awareness (Leybaert et al. 1996; Alegria et al., 1999; Charlier & Leybaert, 2000) Problem Parallel studies using different paradigms make comparisons difficult (LaSasso et al., 2003; Koo et al, in press)

9. Behavioral Data Phoneme Detection Test cent cat Koo et al. (in press)

10. * * Behavioral Data Phoneme Detection Test * p < .05 (2-tailed) Koo et al. (in press)

11. Outline Introduction • Deaf populations • Communication systems • Reading in Deaf populations Functional neuroanatomy of reading in deaf and hearing populations • ASL • English

12. Functional Anatomy of Word Reading Left Inferior Frontal Gyrus Sequencing and control of fine-grained articulatory recoding Phonological Mapping Left Temporo-Parietal Region (Inferior Parietal Lobule/Posterior Superior Temporal Gyrus) Rule-based grapheme-to-phoneme analysis Left Occipito-Temporal Region (Fusiform Gyrus) Linguistically structured memory-based word identification system Pugh et al. (2000)

13. Previous Neuroanatomical work in Deaf Populations Neville et al. (1998) • When reading English sentences, hearing subjects showed strong left lateralization in language processing areas (Left IFG and STS). But deaf subjects did not, instead showing robust right STS activity. • Interpretation: Deaf individuals rely on the right hemisphere for visual-form information when reading and encoding written English. From Neville et al. (1998)

14. Previous Neuroanatomical work in Deaf Populations Deaf > Hearing Aparicio et al. (2007) • During a lexical decision task, French deaf subjects activated the same left IFG, left occipito-temporal and inferior parietal regions as hearing subjects • Deaf subjects showed significantly higher activation in right IFG, left STG, and posterior medial frontal gyrus • Interpretation: Increased use of right IFG and left STG serves as a compensatory mechanism for limited use of the indirect route (assembled phonology) Adapted from Aparicio et al. (2007)