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Cognitive models of spelling and writing Types of dysgraphia

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1 Cognitive models of spelling and writing Types of dysgraphia
What is dysgraphia? Cognitive models of spelling and writing Types of dysgraphia Central dysgraphias Peripheral dysgraphias Nonlexical spelling? Summary

2 What is dysgraphia? A broad division: Central and peripheral acquired dysgraphias (or agraphias) refer to disorders of spelling and/or writing. Dysgraphias that affect spelling are central and those that affect writing are peripheral. Will consider acquired disorders following brain damage (not developmental difficulties).

3 Cognitive model of writing and spelling
Three routes to writing from speech input: 1) Lexical-semantic route. 2) Lexical-nonsemantic route. 3) Nonlexical route. Inner speech? Need to posit separate spoken and written output lexicons in the model because of the many cases of patients who have anomia but not agraphia (and agraphia without anomia). See Ellis & Young, Chapter 7.

4 The lexical semantic route
A word can be recognised as familiar via the auditory input lexicon (PWD patients). The meaning of the word is accessed from the auditory lexicon via the semantic system. The orthographic form of a written word is retrieved via the graphemic output lexicon. The letter representations of a word are assembled via the graphemic output buffer. This route can also be called “spelling via meaning" as only applicable to familiar words.

5 The lexical nonsemantic route
A word is recognised as familiar by activation of representations in the auditory input lexicon. The spoken form of the word is accessed directly via the phonological output lexicon. The written form is retrieved via the graphemic output lexicon using the spoken word form. The letter representations of a word are assembled via the graphemic output buffer. Again, this is only applicable to familiar words.

6 The nonlexical (or sublexical) route
This is assumed to be activated when we spell unfamiliar words such as invented nonwords. It is a metaphor for the application of knowledge about sound-spelling correspondences in order to assemble an oral or a written spelling. Will misspell words that have irregular spellings: e.g.,CASTLE -> "cassel” TABLE -> "taybul” these are called ‘regularisation errors’.

7 Peripheral dysgraphias
Types of dysgraphia Central dysgraphias Phonological dysgraphia Surface dysgraphia Nonsemantic spelling Deep dysgraphia Peripheral dysgraphias Grapheme level impairment Allograph level impairment Motor pattern impairment

8 Phonological dysgraphia
Shallice (1981) reported patient PR. PR’s ability to spell low frequency familiar words was at an above-average level - for example he could spell the word "coniferous". Very poor at spelling nonwords. 2/10 four letter nonwords and 0/10 six-letter words. Errors to nonwords tended to be similar to real words 'lexicalisations': "na" -> gn (from "gnat") "sult" -> ault (from "assault") Had trouble generating letter sounds (/b/ for B).

9 Loss of nonlexical route
Spelling in the absence of phonological mediation (i.e., poor phoneme awareness). Vocabulary or lexically based spelling. Spelling can thus proceed via an autonomous module called the graphemic output lexicon and does not require phonological mediation. Other patients (Baxter & Warrington, 1986; Nolan and Caramazza, 1982; Roeltgen et al., 1986).

10 Beauvois and Derousne (1981) patient RG.
Surface dysgraphia Beauvois and Derousne (1981) patient RG. Spelling unambiguous words GOOD (90%). Spelling irregular words POOR (40%). Spelling nonwords GOOD (100%). RG showed a regularity effect on spelling. e.g., “yacht” --> yot. Could not spell homophones correctly either e.g., “steak” --> stake.

11 Loss of lexical routes Spelling by sound. There is a modular phoneme to grapheme system for spelling words (nonwords OK). Over-reliance on nonlexical route due to impairment of lexical routes. Difficulties with exception words ("island") and ambiguous words ("team") because they require semantic knowledge (Graham, 2000). Other patients (Hatfield & Patterson, 1983; Parkin, 1993b; Weekes and Coltheart, 1996).

12 Nonsemantic spelling? Bramwell’s case of word meaning deafness. This patient could spell to dictation words she could not understand from spoken word input. These words included irregularly spelled words such as the word ‘Edinburgh’. Patterson (1986) reported a similar patient GK. Some patients with dementia show the same pattern i.e. an absence of knowledge about the meaning of a word from any modality but have intact spelling of irregular words (Graham, 2000).

13 Loss of semantic and nonlexical routes
Patterson (1986) proposed the direct route from the auditory input lexicon to the graphemic output lexicon (via the speech output lexicon) thus bypassing the semantic system. This could account for cases of people who can spell irregular words without comprehension. Recent evidence suggests that the semantic system supports the spelling of irregular words - the semantic glue hypothesis (Graham, 2000).

14 Bub & Kertesz (1982) reported patient JC.
Deep dysgraphia Bub & Kertesz (1982) reported patient JC. Made semantic errors when spelling words. e.g., “time” -> clock e.g., “sky” -> sun JC had better spelling of concrete than abstract nouns and this is called an imageability effect. JC also displayed impaired nonword spelling. 5/20 four letter nonwords, 0/17 eight letter nonwords.

15 Loss of nonlexical and nonsemantic routes
Suggests that the route from semantics to the graphemic output lexicon was inoperative. JC did not make semantic errors when reading aloud so this is evidence in favor of separate reading and spelling systems in the brain. JC recovered completely (after 6mths) thus ruling out a developmental explanation of the dysgraphia and also showing the plasticity of spelling skills.

16 One orthographic lexicon or two?
This dissociation between reading and writing underpins contemporary models of written language comprehension and production. Unitary model of writing/reading (Behrmann & Bub, 1992; Allport & Funnell, 1988). Dual lexicon model of writing/reading (Ellis & Young, 1996; Weekes and Coltheart, 1996). Weekes (1996) reported patient NW who was surface dysgraphic and surface dyslexic. Rehabilitation of spelling skills did not affect his reading performance and vice versa.

17 Grapheme level impairment
Miceli, et al (1985) reported patient FV. No aphasia but frequent spelling errors such as additions, deletions, transpositions and letter substitutions in writing to dictation (e.g b for p). Affected oral spelling aloud and handwriting. Affected both word and nonword spelling. Copying was intact. Normal letter formation (intact motor skills). Problem at the grapheme level where abstract letter identity forms are stored and ordered.

18 Allograph level impairment
Goodman & Caramazza (1986). MW. Letter substitutions in handwriting but not spelling aloud (so graphemic level is OK) “starve” -> starze “pierce” -> tierce Letters were well formed - (graphic motor OK) The assignment of shape of written letter form from a graphemic unit is impaired - this is called the allograph level of representation.

19 Other patients Patient JEC (Weekes, 1994). He made frequent case errors (e -> E). Wrote upper case letters well but some lower case letters were written poorly (e.g. b p q d). The spatial similarity of the letters was the best predictor of substitutions, omissions etc. JEC also displayed some surface dysgraphia leading some to argue that peripheral writing errors result from loss of semantic memory (Patterson, Hodges, 1997; Graham, 2000).

20 Types of error letter substitution errors “apple” --> aBBel letter omission errors “swing” --> swin letter addition errors “across -> acccross case substitution errors Queen --> quEEn Letter substitution errors were predicted by the spatial similarity of the lower case target to other lower case letters e.g., b, p, d, & q. crab --> craB; ladder --> laDDer; apple --> aBBel

21 Graphic motor pattern impairments
Selecting letters for written output: Baxter & Warrington (1986): patient I.D.T. Problem in retrieving graphic motor patterns. Could spell aloud (so grapheme level OK). Could copy words and letters well and describe the shape of letters (so allograph level OK). Couldn't write at all - not even three letter words.

22 Other patients Executing (spatial dysgraphia): Ellis, Young & Flude (1987): patient VB. Know the sequence of movements but problem in executing this sequence. Patient tends to write down one side of page. Patient omits or duplicates letters and strokes. Problem attending to visual and kinaesthetic feedback during writing?

23 Summary Studies of dysgraphic patients reveal that spelling and writing depend on multiple routes. and the functional architecture of the normal spelling/writing system is highly modular. The evidence from surface dyslexic and dysgraphic patients suggests that there is more than one orthographic lexicon used for reading and writing although this hypothesis awaits converging data from brain imaging.

24 Readings Parkin Chapter 8. Ellis & Young (Chapter 7&8).
Graham, N. (2000). Dysgraphia in dementia. Neurocase, 6, Graham, N. Patterson, K & Hodges, J (2000). The impact of semantic memory loss on spelling: evidence from semantic dementia. Neuropsychologia,38, Weekes, B (1994). A cognitive neuropsychological analysis of allograph errors from a patient with acquired dysgraphia. Aphasiology, 8(5), Weekes, B.S. & Coltheart, M. (1996). Surface dyslexia and surface dysgraphia: Treatment studies and their theoretical implications. Cognitive Neuropsychology, 13(2),

25 Weekes and Coltheart (1996)

26 One example of this is the fact that the dissociation between letter naming and word recognition provides strong evidence for the modularity of letter specific and word level representations (Berhmann and McLeod, 1995). Similarly, the dissociation between impaired reading and preserved writing (the latter being a more difficult task) is among the strongest pieces of evidence in favor of the view that reading and writing are modular skills. The phenomenon of alexia without agraphia is also germane to the issue of whether there is one lexicon (Behrmann and Bub, 1992) or two lexica (Weekes and Coltheart, 1996) for reading and writing.

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