lecture 3 - acquired dyslexia

Joseph Dejerine looked at the case of Mr C. Mr C died from a stroke - he was unable to recognise words or letters but he could speak fine, recognise people and remained suprisingly tactile.

looking at Mr C's post-mortem, Dejerine concludes his pure verbal blindness was a result of a disconnection between the primary visual areas and the ventro-occipital temporal region (Cohen et al, 2000)

FMRI data of patients similar to Mr C show the same disconnection that Dejerine suggested. there is a linear relationship between word length and reading time in these patients

therefore, Dejerine was the first person to suggest pure verbal blindness or pure alexia results from a disconnection between these regions, and this is one form of acquired dyslexia
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Joseph Dejerine looked at the case of Mr C. Mr C died from a stroke - he was unable to recognise words or letters but he could speak fine, recognise people and remained suprisingly tactile.

looking at Mr C's post-mortem, Dejerine concludes his pure verbal blindness was a result of a disconnection between the primary visual areas and the ventro-occipital temporal region (Cohen et al, 2000)

FMRI data of patients similar to Mr C show the same disconnection that Dejerine suggested. there is a linear relationship between word length and reading time in these patients

therefore, Dejerine was the first person to suggest pure verbal blindness or pure alexia results from a disconnection between these regions, and this is one form of acquired dyslexia
French neurologist Joseph Jules Dejerine (1849-1917) is particularly famous in the
domain of acquired reading disorders. What for?
peripheral includes:
pure Alexia, attentional dyslexia and neglect dyslexia

central includes:
phonological, deep, semantic and surface
what's the difference in peripheral and central dyslexias?
the inability to recognise words or letters but can speak fine and spelling is intact

this is letter-by-letter reading. it is heavily affected by whether the font is ambiguous or not, therefore contextual information (e.g s_ile) is not helpful to them

it is associated with damage to the visual word form area or damage to the region just before this. info from the left visa hemi-field initially processed in the right, needs to cross to the left to be combined with the light - if the corpus callosum is damaged then transer is not possible
what is pure alexia?
pure Alexia - they don't take account of context whereas attentional dyslexia they take too much account of context
how is pure Alexia and attentional dyslexia different?
letters migrate to and switch between neighbouring words

they can recognise vowels or letters on their own easily, but as soon as they are put into a word they are errorprone
what is attentional dyslexia?
failure to identify the initial or final letters of a word, resulting in omission, substitutions or additions

e.g. lend > 'end', wine > 'mine', oat > 'boat'

there are 3 levels of abstraction linked to neglect dyslexia:
1. tied to retinal image location
2. independent of retinal image but orientation matter
3. independent of location and orientation
what's (left)neglect dyslexia?
..central dyslexias
moving onto..
this is when there is an inability to read new or made up words - this is due to phonological impairment meaning the ability to manipulate basic sounds in language is difficult

this points to an impairment in the non lexical route in the DRC - knowledge of rules and application of the rules is faulty

but they can read regular, irregular and frquent-abstarct words perfectly
what's phonological dyslexia
associated with damage to the left hemisphere and consists of inability to read non-words

they often make semantic areas e.g if shown sick > ill, tree > bush

it has also been found these patients have stronger performancee when the word maps onto something concrete e.g they can read 'dog' as it maps onto something concrete (dogs smell) whereas they struggle with wise

the DRC explanation would suggest only the semantic route is intact - the word selected for output is not the target word but is semantically associated
what is deep dyslexia?
these patients can read words fluently but they do not understand the meaning suggesting the semantic route is not intact

The case of WLP- had semantic dementia. Could read pseudowords, 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)
what is semantic dyslexia?
if you can read regular words and pseudowords but cannot understand the meaning, there must be a direct route. Before this reading was thought to involve only a semantic route and a grapho-phonological route.how did semantic dyslexia lead to a revision of the DRC?What is imapired is the surface of the words. Not the meaning of the words but why they're formed the way they are The main symptom: regularisations - low frequency irregular words like 'pint' rhyming with 'mint' There is also a 'stress-shift' i.e guitar is pronounced GUItar (geeetar) rather than guitar. We pronounce it normally guitar because we know of the exception and that this word is not pronounced GUItar Failures to apply contextual rules e.g guest pronounced as just - this is because sometimes 'g' is pronounced as 'j' but because we know there is a 'gu' together we know the g will pronounced 'guh'. Therefore this shows the failure to use the context of the letters to pronounce the word correctlywhat is surface dyslexia?this is called semi-alexia info from the left visual field, initially processed by the right needs to cross to the left to be combined with the right in the visual-word form area. but if the corpus callosum which allows communication to occur, is broken then this transfer cannot happen. so they can only read words presented to the left of the visual field Cohen 2001 found the visual word form area did not light up when p's presented with stimuli on the left, but it did light up when presented to the rightwhat happens when someone can't read info shown to the left of a fixation point?