M4, T2, Types of dyslexia and explaining dyslexia via word recog models Flashcards
Dyslexia
Dyslexia – reading deficit/problems
Acquired Dyslexia – reading problems and deficits due to brain injury or damage
Developmental Dyslexia – failing to meet age relevant reading standards with normal intellectual functioning and educational opportunities for reading
Earliest cases of dyslexia
- Dejerine (1891) patient with dyslexia and dysgraphia, (i.e., deficit in reading and spelling/writing respectively) due to infarction in left parietal lobe
- Dejerine (1892) patient demonstrated a dissociation between reading and writing
- Patient could write well but could not read printed words aloud or for comprehension
- He could therefore not read things he had written
Types of dyslexia
Peripheral dyslexias: affect early stages in word recognition
visual analysis of letters or words
Central dyslexias : affect deeper processes
- grapheme-phoneme conversion
- orthographic input lexicon
- semantic access
Types of peripheral dyslexia
- neglect dyslexia
- pure alexia
- letter position dyslexia
- attentional dyslexia
Neglect dyslexia, Brain (1941)
- Right hemisphere damage (parietal lobe) -> unilateral neglect
- Patient does not attend to left side of space
Neglect Dyslexia – described by Brain (1941)
- Neglect dyslexia patient does not read left/right half page or word (Haywood & Coltheart, 2000)
- Not a consequence of unilateral neglect, can co-occur with unilateral neglect
- Errors for reading printed words – failure to identify part of/portion of word, page of text
Neglect dyslexia - examples
Neglect Dyslexia Left side
liquid -> squid
cage -> rage
yellow -> pillow
Neglect Dyslexia Right Side
book -> boot
milk -> mill
pen -> pet
Neglect dyslexia - defining symptoms (errors)
- Errors are spatially determined visual errors consistently in left/right side of a word -> a neglect point in visual word reading
- All letters correct on preserved side
- Letters incorrect on the neglected side
- Errors – very similar to original word in length
- reading deficit occurs due to difficulty in specification of the word at the level of visual orthographic analysis
Pure alexia
- Letter-by-Letter Reading or Alexia without Agraphia
- Writing and spelling unaffected
- Reading printed words is problematic
- Brain damage/lesion typically located inferior portions of occipital lobe bordering on temporal lobe in left hemisphere also damage to posterior portion of corpus callosum
How pure alexia presents
- Can identify letters
- Reads words aloud - say one letter at a time – defining symptom
CHAIR -> C…H…A…I…R -> “chair” - Patient names (or misname) some or all of the letters before a response is made
- If patient can name all letters, then will correctly say word
- Response times increase as word length increases (e.g., 10 seconds per letter within a word)
- Occasionally patient can name short words without spelling e.g. ball
- Role of letter confusability in pure alexia reading ability
X, J vs C, G, Q
Pure alexia and the word recog model
- Brain damage results in problem with early visual processing letter features
- Impaired visual orthographic analysis
- Word information going to reading system is noisy
Letter position dyslexia
- Primary error – letter transposition e.g., broad -> board
- Migration or transposition letters tend to be within word not initial or final letters
- Patient data Hebrew readers – lot of possible transposition words compared to English
- Correct letter identification but position coding of letters problematic
jugde vs. judge - deficit at visual orthographic analysis
Attentional dyslexia
- Person can read a single letter or a single word in isolation but cannot read the same word or letter if it is shown with items of the same type
- Between-word letter migration errors – letter in one words appears within the other word
-> Presented with WIN FED says FIN FED
-> BFXQL asked to identify centre letter, says F or Q not X - Problem with narrowing attention
- Deficit letter to word binding
Attentional dyslexia - brain stuff and particular region of word recog model
- Exact location of brain lesion unknown but patients typically have damage to posterior left-hemisphere including subcortical structures
- Difficulty with the visual specification of the word at the visual orthographic analysis level
Types of central dyslexia
- surface dyslexia
- phonological dyslexia
- direct-route dyslexia (lexical non-semantic reading)
- deep dyslexia
Surface dyslexia
- Regular words read better than irregular words
-> MINT FEAR VS PINT BEAR - Preserved regular word and nonword reading
- Many patients worse at reading nonwords than matched real words
- Errors
-> Regularisations (yacht, sew)
Surface dyslexia - impaired pathways
- intact grapheme-phoneme conversion rules
- impairment of lexical route to reading aloud
-> Orthographic Input Lexicon
-> Orthographic Input Lexicon to Semantic System
-> Orthographic Input Lexicon output to the Phonological Output Lexicon
Phonological dyslexia
- Poor or flawed nonword reading
- Problems reading new words
- Nonwords might be read as visually similar words
SOOF -> soot - OK for well known (familiar) words
- Impaired sub-lexical (non-lexical) route to reading aloud
Phonological dyslexia - impairment pathways
Impaired sub-lexical (non-lexical) route to reading aloud
-> impaired grapheme-phoneme conversion module
-> impaired access to the grapheme-phoneme conversion module
-> impaired output from the grapheme-phoneme conversion module to the phonological output buffer
Phonological dyslexia - impaired grapheme-phoneme conversion module
- Non-word reading is non-existent
- Learning to read new words is non-existent via sounding out
Phonological dyslexia - impaired (slowed) output from the grapheme-phoneme conversion module to the phonological output buffer
Some phonological dyslexics better at reading nonwords when these are pseudo-homophones (nonwords that sound like real words e.g. brane) than when they are non-words unlike a real word (e.g. frane)
Phonological dyslexia - impaired input into grapheme-phoneme conversion
- Some non-words have one-to-one mapping between letters and sounds (graphemes and phonemes) e.g. trov
- Some non-words have a letter that must be combined to form a sounds (phoneme) e.g., thoo, which is graphemic parsing
- If there is a problem (noise) in the letter information coming into the Grapheme-Phoneme Conversion module phonological dyslexics will have more problems with non-words that need graphemic parsing
Direct-route dyslexia
- also known as lexical-nonsemantic reading
- patient does not know the meaning of the word
- patient can still read printed irregular words aloud
Deep dyslexia
- First systematic study – Marshall & Newcombe (1966)
- Typically an acquired reading impairment
- Cases of developmental Deep Dyslexia in the literature
- Defining symptom semantic error in reading aloud
- Symptoms of Deep Dyslexia typically unvarying across cases
Deep dyslexia - symptoms when reading aloud
- Semantic errors
- Visual errors
- Visual-then-semantic errors
- Morphological errors
- Very poor non-word reading
- Imageability effect in reading words
- Content word reading better than function word reading
- Function word substitutions
Deep dyslexia - semantic errors
Key symptom
Tandem -> cycle
Cost -> money
Decay -> rubbish
Deep dyslexia - visual errors
Visual errors
Signal -> single
Decree -> degree
Visual-then-semantic errors
Sympathy (symphony) -> orchestra
Favour (flavour) -> taste
Charter (chart) -> map
Deep dyslexia - morphological errors and poor nonword reading
Morphological errors (derivational errors)
Edition -> editor
Courage -> courageous
Very poor nonword reading (nonsense words)
Wux -> don’t know
Nol -> no idea
Deep dyslexia - imageability effect
Better at reading concrete than abstract words
- Better at saying ‘butter’ and ‘windmill’ than ‘grief’ and ‘wish’
- Errors abstract words -> visually related imageable words
Deep dyslexia - content v function words
Content words (nouns, verbs, adjectives)
Function words (was, quite, of)
Function word errors
Was -> with
If -> yet
Quite -> perhaps
Yes -> small words are the worst
Deep dyslexia - spelling and writing
- Spelling and writing may be impossible
- If spelling and writing possible then symptoms are equivalent to those listed for reading printed words aloud
- Majority of patients with deep dyslexia show all of these symptoms
Explanations for deep dyslexia
Impairment(s) to the normal left hemisphere reading system through many different locations of damage
OR
Reading occurs via a secondary right hemisphere reading system
Deep dyslexia and the left hemisphere reading model part 1
- Damage Grapheme-phoneme conversion– inability to read non-words
- Damage Semantic System - semantic errors, and imageability effect
- Damage Orthographic Input Lexicon- visual errors
- Impaired connection between orthographic input lexicon and phonological output lexicon – poor word reading and function word errors
Deep dyslexia and the left hemisphere reading model part 2
- Damage to connection between semantic system and phonological output lexicon – patient correctly understands a printed word but makes a semantic error reading it
- Damage to component syntactic system processes prefixes and suffixes (morphological errors)
Deep dyslexia and right hemisphere hypothesis
- If the left hemisphere cannot complete (orthography, semantics or phonology) then the right hemisphere reading system must take over
-> Coltheart (1980, 2000) Deep Dyslexia is a loss access in the Orthographic Input Lexicon in the left hemisphere (cannot read printed words)
Deep Dyslexic reads “words” - via Orthographic Input Lexicon in the Right Hemisphere
- Activates semantic system representation in the Right Hemisphere
- Information from Right Hemisphere semantic system sent to the Phonological Output Lexicon in the Left Hemisphere (needed to say word aloud)
*look up image
Explaining deep dyslexia errors via the right hemisphere reading
- Grapheme-Phoneme conversion non-existent in right hemisphere - nonword reading errors
- Imageability effect - visual field studies show better performance for concrete than abstract words in right hemisphere
- Semantic errors made in patients with no left hemisphere
- Semantic errors may also result from incorrect target selection being transferred to left hemisphere or incomplete semantic word representation to start with
- Function words are poorly represented within the right hemisphere
Deep dyslexia and right hem reading, syntactic processing and visual errors
Syntactic processing in right hemisphere not as good as left hemisphere - morphological errors
May also explain the visual errors – poorer word representation in right hemisphere and therefore visually close word is selected as target words
Deep dyslexia relevant brain regions (Coltheart, 2000)
- Coltheart (2000) imaging study relevant areas include:
- Orthographic processing – left occipital and occipitotemporal regions
- Semantic processing – border between superior and middle temporal gyrus, areas BA21 and BA22 (Left Hemisphere)
- Phonological output – left hemisphere frontal operculum
*look up images (3)
