Acquired dyslexia syndromes - week 5 (Nicholas) Flashcards
(18 cards)
French neurologist Joseph-Jules Déjerine and Monsieur C. (1892)
Mr C. is a 68 year-old intelligent, cultured, wealthy retired Parisian textile merchant, whom following a stroke wakes up one day of 1887 with the inability to read. He is unable to recognize words or letters, however:
Oral language AND spelling are intact.
Object, face, drawing and even number recognition largely preserved.
Surprisingly, tactile and gestural letter/word recognition remains intact.
Mr C. dies in 1892 due to another stroke.
After postmortem, Déjerine concludes that Mr C.’s ‘pure verbal blindness’ results from a disconnection between primary visual areas and an other occipital area dealing specifically with letters and words.
We now know that this region is located in the ventral occipito-temporal region (Cohen et al., 2000)!
‘Pure verbal blindness’ or ‘pure alexia’ (i.e. without agraphia) typically results from this region being either damaged or disconnected and this is one type of acquired reading disorder.
Peripheral dyslexias
refers to any reading disorder in which seeing a word as a stable orthographic object fails.
Central dyslexias
refers to any reading disorder in which impairment occurs after the stage of visual word form.
Classification of acquired dyslexias
Two types of acquired reading disorder can be distinguished: the peripheral dyslexias and the central dyslexias.
For a word to be understood or pronounced, it must first be perceived as an orthographic entity, i.e., seen as a ‘legal’ visual word form.
Types of peripheral dyslexias
Pure alexia/alexia without agraphia/letter-by-letter reading (Déjerine, 1892)
Attentional dyslexia (Shallice & Warrington, 1977)
Neglect dyslexia (Ellis, Flude & Young, 1987)
Types of central dyslexias
Phonological dyslexia (Beauvois & Derouesné, 1979)
Deep dyslexia (Marshall & Newcombe, 1973)
Semantic dyslexia (Schwartz, Marin & Saffran, 1980)
Surface dyslexia (Marshall & Newcombe, 1973)
Pure alexia (Déjerine, 1892)
Other names: ‘alexia without agraphia’ (i.e. no concurrent spelling impairment), ‘letter-by-letter reading’
Many cases described, and Mr C. was the first!
Main symptom: Word identification impossible, except via explicit sequential identification of individual letters (slow and painful).
Hence, substantial length effect and almost a linear relation between length in letters and reading time.
The ‘Saffran effect’ (Saffran & Coslett, 1998)
Pure alexics are well above chance in categorizing the meaning of a word (is it an animal?) or lexical status of a letter string (is it a real word?), despite their inability to “consciously” identify the word.
Cerebral area involved: visual word form area (VWFA; ventral occipito-temporal region) damaged or disconnected.
Damage of VWFA
- Pure alexia is typically associated with either a damage directly to the visual word-form area, or a disconnection preventing information to reach that region.
Hemi-alexia
(Patient A.C.)
-As you know, information from the left visual hemi-field, initially processed in the right hemisphere, needs to cross to the left hemisphere to be combined with the right hemi-field information in the visual word-form area. But if the corpus callosum, which allows communication between the hemispheres, is damaged, then this transfer may no longer be possible. As a result, the patient has difficulty reading only words that are presented in the left visual field. This condition has been termed ‘hemi-alexia’. It is NOT to be confounded with hemi-neglect dyslexia.
-In patient AC the visual word-form area (i.e., left hemisphere) is NOT activated by strings presented in the left visual field, unlike controls. By comparison, for strings presented in the right visual field, AC lights up his/her visual word form area normally.
Attentional dyslexia (Shallice & Warrington, 1977)
Very rare!
Associated with left parietal lesion.
Difficulty in identifying letters or words when flanked by other items of the same category
However, naming of a letter or a word in isolation preserved.
‘o’ on its own is fine, but errorprone in ‘word’;
‘word’ on its own is fine, but erroprone in ‘when the word is in a sentence’.
Also, migration of letters to analogous position in other words, i.e. left hemisphere > ‘heft hemisphere’.
Disorder of the ‘attentional filter’: the window of attention is larger than the target part of the visual field, and this lets other information in.
It is specific to reading, as it does not hold for pictures (Warrington, 1993).
The nature of the flankers modulates the manifestation of the disorder: less interference with different-category than with same-category distractors!
Neglect dyslexia (Kinsbourne & Warrington, 1962)
Main symptom: failure to identify the initial or final letter(s) of a word or group of words, resulting in omissions, substitutions or additions.
Often but not necessarily associated with spatial neglect.
Typically, contralateral parietal lesion.
In the most common form, the initial portion of the word is problematic (i.e. right lesion).
e.g. lend > ‘end’, wine > ‘mine’, oat > ‘boat’
Most often, there are as many erroneous letters to the left (or the right) of the neglect point as neglected letters in the target.
car > bar, enigma > stigma (as opposed to sigma)
Thus, some processing of the neglected letters occurs: suggests that position is preserved, but identity is lost.
Phonological dyslexia (Beauvois & Derouesné, 1979)
Main symptoms: Impaired ability to read new or made up word (or nonwords), and to sound out individual graphemes.
Lesion of the temporal lobe of dominant hemisphere.
But reading of words relatively intact, if not perfect (see below); visual processing of letter strings intact; and immediate repetition of nonwords perfect.
Some patients read concrete words better than abstract words, and/or show difficulty with function (as opposed to content) words.
Deep dyslexia (Marshall & Newcombe, 1973)
Associated with extensive damage to the dominant (L) hemisphere, and consists of:
Impaired ability to read nonwords.
Semantically related errors: ill > ‘sick’, bush > ‘tree’, bad > ‘liar’
Visual errors: life >’wife’, sword >’words’
Derivational errors: card > ‘cards’, fleeing > ‘flee’, entertain > ‘entertainment’, beg > ‘beggar’
Effect of syntactical class:
nouns > adjectives > verbs > functors
Effect of imageability: concrete > abstract words
But why the semantic errors?
The semantic route is by default inaccurate when it comes to selecting word for speech production.
The patient has no information about the target word other than its meaning.
This would explain imageability effect, and low performance on functors.
Surface dyslexia (Marshall & Newcombe, 1973)
Main symptoms:
Regularisations (typical pronunciation chosen), especially for low frequency irregular words, e.g., ‘pint’ rhyming with ‘mint’
Stress shift, e.g. guiTAR > ‘GUItar’
Comprehension based on pronunciation, e.g., bear as ‘alcoholic beverage’ (beer).
Failures to apply contextual rules, e.g. insect > ‘insist’, guest > ‘just’
Incomplete decoding of digram vowels, e.g. niece > ‘nice’
However, reading of regular words and nonwords spared!
Traditional interpretation: Inability to read via the lexical route; reading reflects the exclusive reliance on the nonlexical route and thus on GPCs.
Indeed, strong sensitivity to regularity as a ‘critical variable’ (cf. next Table).
Semantic dyslexia/ Reading without meaning (Schwartz, Marin & Saffran, 1980)
Disorder associated with neurological disease (e.g. Alzheimer, semantic dementia).
Main symptom: ability of patients to read fast and fluently (even irregular words in some patients), but inability to comprehend what they are reading.
‘I don’t know the word, I can only read’ (from McCarthy & Warrington, 1982).
Most patients evolve towards surface dyslexia, which itself is associated with semantic disorders.
The case of WLP (Schwartz et al., 1980)
Patient with semantic dementia.
WLP can read pseudowords (made-up words), match a spoken word (‘brain’) with a written pseudohomophone (brane), and read aloud irregular words (pint), which by contrast she can not define or match with a picture.
BUT she fails in an object naming task (1/70), although she can mimic the use of certain objects (thus poor conceptual knowledge)
