Week 7 - Alexia PDF

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Detailed notes on types of alexia and the routes ...

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Alexia Alexia (or acquired dyslexia) refers to an acquired disorder in reading caused by brain pathology (Benson and Ardila, 1996). A cluster of disorders that occur after brain damage. Two case reports represent important milestones in the study of alexia: 1) 1981, a patient suffered a cerebrovascular accident that produced some degree of right-sided visual field defect and mild difficulty in naming and in understanding spoken language together with a complete loss of the ability to read. The patient could write nothing but his signature. Spoken language improved, but the alexia and agraphia remained unchanged until death. Postmortem showed an old infarct in the left parietal lobe. 2) 1982, patient had an inability to read but no other language disturbances. This patient couldn’t read apart from a few individual letters, but could write. The infarct involving softening of the left angular gyrus was the source of alexia without agraphia. Alexia with agraphia – parietal-temporal alexia, or central alexia Alexia without agraphia – occipital alexia, or pure alexia Pathology in the frontal language areas = frontal alexia Reading difficulties associated with right hemisphere = spatial alexia These 4 types of alexias represent the neurological classification of alexias. Significant variability, however, has been observed in the pattern of disturbances; a new approach was developed – the psycholinguistic or cognitive perspective of alexias. Interest shifted from anatomical correlates, to the functional mechanisms underlying them. The linguistic and cognitive approaches to alexia required the development of models for normal reading. Most of these models propose that after initial letter identification, reading proceeds along two linguistically different routes: 1) The direct route, where the written word is associated with a visual word in lexical memory 2) The indirect route, where the written word is transformed into a spoken word following a graphophonemic set of rules, and the meaning is attained through its phonological mediation. If one or the other is altered, different error patterns can be observed.

Alexia subtypes Alexia without agraphia (occipital/pure alexia) Core clinical features – disturbance in reading contrasted with writing competency. They are unable to read what they have just written. They can read letters but not words. Sometimes the patient fragments the letter e.g. says I for K. Letter-by-letter reading eventually results in word recognition sometimes. They appear to use an inefficient eye movement strategy when reading, fixating to the left; less of the word is then processed. Not only is the recognition of letters and words impaired, but also that of fragmented pictures, suggesting an inefficient build-up of sensory representations (Starrfelt et al, 2010). The process of reading individual letters aloud to recognise the word is slow, and open to error, especially on long words; reading time is proportional to the number of letters. This affect differs according to the degree (Sheldon et al, 2012). Morphological paralexias (misreading final morphemes) is a common characteristic e.g. closed for closing. They can recognise words spelled out to them, can recognise letters outlined on hand. Can match letters with different writing forms. Damage involves left medial and inferior occipital reading. The abstract letter identities (visual word form) ar subtended by a restricted patch of left-hemispheric fusiform cortex, which is activated during reading (Kleinschmidt & Cohen, 2006). Alexia with agraphia (central/parietal-temporal alexia) Core clinical features – impairments of reading and writing. Impaired ability to read aloud and comprehend written language. Inability to read letters – total alexia. Patients fail to recognise a spelled out word. Their ability to copy written/printed words is much better than their ability to write them spontaneously or from dictation. Reading of other symbolic systems e.g. musical notation is also likely impaired. Can result from cerebrovascular disease involving the angular branch of the left middle cerebral artery. Trauma to the temporal-parietal region. Damage to white matter in the left inferior parietal lobe. Frontal alexia Core clinical features – often found in Broca’s aphasia; understand some written material but limited to individual words. Word recognised are almost always limited to content words (nouns/verbs). They insist they cannot read and avoid doing it. Reading aloud is agrammatic. It resembles their AC disturbance (Benson, 1977). Will read some meaningful words but fail to read individual letters in a word. Can recognise some words spelled aloud but have difficulty comprehending most words. Reading comprehension is superior to reading aloud; same speech problems as spontaneous lang. Abnormal condition affecting posterior area of the left frontal lobe. Spatial alexia Core clinical features – deficits in recognising visuospatial arrangements of words and text. Difficulty in comprehending written material Inability to fix gaze on words, and move from one line to another; neglect of the left side of the text. Inability to follow lines of text; grouping and fragmentation of words due to inability to correctly interpret relative value of spaces between letters.

Right hemisphere pathology – spatial disturbances, specific representation of neglect for words may be independent of representational neglect for objects. Psycholinguistic models of alexias Usually introduce a major distinction between central and peripheral alexias. Central – involve high-level linguistic processing; patient can perceive a word correctly but has difficulties recognising it with either semantic or phonological processing. 3 different types each feature a specific pattern of reading errors: a) phonological; b) surface; c) deep. Peripheral – early stages of reading impairment appears to have more connection to a perceptual disturbance; has difficulty attaining satisfactory visual word processing. Difficulty perceiving the written word. Usually 3 main types: a) letter-by-letter reading; b) neglect alexia; c) attentional alexia. Central alexias a) Phonological alexia – the inability to read legitimate pseudo-words, despite well-preserved ability to read real words. Lexicalisation e.g. blaf read as black. Absence of semantic errors. This dissociation suggests that the phonological, or indirect, reading route is impaired, and reading must rely on the lexical, or direct, route. High frequency words are likely to be read, whereas pseudo-words (zero frequency) are impossible. Real words are stored in lexical memory, where pseudo-words are not. Patients cannot use spelling-to-sound correspondence rules in written language. When reading, visual paralexias are observed; the patient will read real words as other visually similar words, which will have many letters in common e.g. mild becomes slid. Damage in reading pseudo-words associated with a relatively intact word reading ability is often due to damage in the left frontal operculum. b) Surface alexia – the indirect route is available, and the direct route is impaired. Superior reading of regular words and legitimate pseudo-words, compared to irregular words. Legitimate pseudo-words can be easily read because they rely on the indirect route. The overuse of the preserved phonological route will result in ‘regularisation errors’. Friedman (1998) says it is characterised by: - Regularisation errors always observed (irregular words are phonologically read), but with variable frequency - Associated with lexical agraphia - Fluent aphasia found in most cases - Left temporal lesion c) Deep alexia – if both the direct and indirect routes are impaired, only limited residual reading ability will remain: - Semantic paralexias are observed (word associates e.g. lawyer is read as attorney) - Success in reading a word is affected by grammatical category e.g. concrete nouns better than abstract - Pseudo-words cannot be read. Semantic errors. - Always associated with agraphia Commonly extensive left-hemisphere insults. Deep alexia represents reading that relies on righthemisphere orthographic and semantic processing.

Peripheral alexias a) Attentional alexia – read single words but unable to read multiword displays, or to name constituent letters of the word. Presented deep left parietal tumours. Deficit in selective attention.

Direct lexical route - the inability to read legitimate pseudo-words, despite well-preserved ability to read real words. Phonological route is impaired. Phonological, or indirect, reading route is impaired, and reading must rely on the lexical, or direct, route Reading aloud involves a lexical, but not semantic, route. This route can be used to read: - Real words, irrespective to their spelling-to-sound regularity - Variables such as imageability or concreteness should not affect performance

Indirect/sub-lexical route – orthographic-to-phonological conversation, sounding out The indirect route is available, and the direct route is impaired. Superior reading of regular words and legitimate pseudo-words, compared to irregular words. Legitimate pseudo-words can be easily read because they rely on the indirect route. The overuse of the preserved phonological route will result in ‘regularisation errors’. Friedman (1998) says it is characterised by: - Regularisation errors always observed (irregular words are phonologically read), but with variable frequency - Associated with lexical agraphia - Fluent aphasia found in most cases - Left temporal lesion Reading aloud involves parsing and phonological assembly – blending a string of phonemes into a

word

Semantic lexical route if both the direct and indirect routes are impaired, only limited residual reading ability will remain: - Semantic paralexias are observed (word associates e.g. lawyer is read as attorney) - Success in reading a word is affected by grammatical category e.g. concrete nouns better than abstract. Disambiguation of homographs. - Pseudo-words cannot be read - Always associated with agraphia Commonly extensive left-hemisphere insults. Deep alexia represents reading that relies on righthemisphere orthographic and semantic processing....