the neural signature of reading in deaf individuals
TRANSCRIPT
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