the neural signature of reading in deaf individuals

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

Outline

Introduction– Deaf populations– Communication systems– Reading in Deaf populations

Functional neuroanatomy of reading in deaf and hearing populations

– ASL– English

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

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?

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

Cued Speech

ASL and Cued Speech

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 CuersSkilled readers who show strong phonological awareness (Leybaert et al. 1996; Alegria et al., 1999; Charlier & Leybaert, 2000)

ProblemParallel studies using different paradigms make comparisons difficult (LaSasso et al., 2003; Koo et al, in press)

Behavioral DataPhoneme Detection Test

cent cat

Koo et al. (in press)

0

500

1000

1500

2000

2500

3000

3500

4000

Reaction Time

Time (

ms)

Hearing

Deaf Cuers

Hearing ASL

Deaf ASL

0

0.2

0.4

0.6

0.8

1

1.2

Accuracy

Hearing

Deaf Cuers

Hearing ASL

Deaf ASL

Behavioral DataPhoneme Detection Test

* p < .05 (2-tailed)

Koo et al. (in press)

**

Outline

Introduction– Deaf populations– Communication systems– Reading in Deaf populations

Functional neuroanatomy of reading in deaf and hearing populations

– ASL– English

Functional Anatomy of Word Reading

Pugh et al. (2000)

Left Occipito-Temporal Region

(Fusiform Gyrus)

Linguistically structured memory-based word identification system

Left Temporo-Parietal Region

(Inferior Parietal Lobule/Posterior Superior Temporal Gyrus)

Rule-based grapheme-to-phoneme analysis

Left Inferior Frontal Gyrus

Sequencing and control of fine-grained articulatory recoding

Phonological Mapping

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)

Previous Neuroanatomical work in Deaf Populations

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)

Deaf > Hearing