Subtypes of Developmental Dyslexia & Universality?

core phonological processing deficit theory - but individual variation in ability to store & retrieve different types of written & spoken info across dyslexics .. so .. not homogeneous disorder!

double deficit hypothesis - wolf & bowers, 1999

core phonological processing deficit
- difficulty in processing small units of sound
- snowling, 1995 - inhibits development of letter-sound mappings that are required for reading novel words

double-deficit hypothesis
- wolf & bowers, 1999 - dyslexic symptoms include not only a deficit in phonological processing (accuracy) but also a deficit in central processing speed (fluency)

+ for d-d hypoth
- sirling & miles, 1988 - dyslexics tend to speak slower than non-dyslexics
- felton, 1990 - rapid naming is a persistent problem for many dyslexics

developmental phonological dyslexia - temple & marshall, 1983
- 17y/o f - HM
- avrg. verbal intelligence
- unexpectedly low reading age of 10y11m
- v. poor at reading nonwords
- good at reading aloud words
- sublexical route poorly developed
- snowling & hulme, 1989 - often associated with underlying deficit in phonological awareness

discrete subtypes vs continuum
- castles & coltheart, 1993 - discrete
- ellis, 1996 - continuum

developmental deep dyslexia - start & howard, 1995
- 13y/o f - KJ
- below avrg intelligence
- reading age of 6y2m
- semantic/vis/morphological errors
- underlying semantic deficit

RH hypoth - pitchford & morgan, 2007
- 29y/o f - JPJ
- history of difficulties with learning to read
- good receptive & expressive vocab
- poor auditory-verbal mem & poor nonword repetition & reading
- fMRI - RH hyperactivation during imageable word & nonword reading
- indicates strategic use of RH mem. systems in order to compensate for the lack of phonological processing

dual route theory - forster & chambers, 1973; baron, 1977

grain size theory - ziegler & goswami, 2006

- paulesu, 2001 - dyslexia has universal basis in the brain

- siok, 2004 - impaired chinese readers showed reduced activation of large neural circuits - so.. maybe phonological deficits aren't universal cause of dyslexia at a biological level