Neuropsychology: The Literate Brain Flashcards
What is reading as a learned expert system?
-Reading and writing essentially cultural invention of great significance
-Literacy emerged 5000years ago, became universal in Western cultures 100years ago (much of world still illiterate)
-Acquiring literacy requires constructing dedicated neural/cognitive system
-Likely to derive from core set of other (evolved) abilities: visual recognition, speech processing, learning and memory
-Cultural recycling: pre-existing functions recruited to support cultural invention (interactions in both directions)
What are the cognitive mechanisms for visual word recognition?
-Series of processing stages: starting with general visual processes
-Evidence for top-down effects in visual processing
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Which hierarchical processing stages are involved in reading?
-Detection for visual features
-Letter recognition
-Visual word recognition
-Meaning (semantics)
How is feedback (top-down) used in visual processing?
-Using feedback from letter recognition to fill in obscured letter features: semantic influences on lexical decision
-Using feedback from word recognition
–>Word superiority effect: filling in letter to create existing words rather than nonsense words
–>Ambiguous graphemes: context of ambiguous graphemes determines which words to use
-Using feedback from meaning to see effect of semantics on word recognition: context can prime certain words to be recognized
How is the visual word form area (VWFA) a neural mechanism for reading?
Responds to written words more than consonant strings or false fonts (irrespective of which part of space they are displayed in)
What are other characteristics of the visual word form area?
-Responds to learned letters (true fonts) compared to pseudo-letters (false fonts) of comparable visual complexity (Price, Wise & Frackowiak, 1996)
-Repetition priming suggests it responds to both upper and lower case letters even when visual dissimilar (Dehaene et al., 2001)
-Subliminal presentation of words activates area, suggests automatic access (Dehaene et al., 2001)
-Electrophysiological data comparing true and false fonts suggests that region activated early, around 150-200msecs after stimulus onset (Bentin, Mouchetant-Rostaing, Giard, Echallier & Pernier, 1999)
What are the neural mechanisms for visual word recognition?
-Left occipitotemporal sulcus: small words, frequent substrings and morphemes and local bigrams
-Bilateral area V8: bank of abstract letter detectors
-Bilateral area V4: letter shapes (case-specific)
-Bilateral area V2: local contours (letter fragments)
-Bilateral area V1: oriented bars
-Bilateral thalamus (lateral geniculate nucleus): local contrasts
What does the underlying functional organization look like of reading?
Complex: not just 1 region
(image)
What is pure alexia?
-Problem in visual word recognition
-Letter-by-letter reading, reading disorder with problems with recognizing letters and words
–>Possibly by disruption of parallel processing of letter strings
-Damage to/near visual word form area
-Not due to low-level visual problems, but still struggle under perceptually demanded conditions
–>Controversy about whether deficit reflects visual processes or reading-specific processes
-Example of peripheral dyslexia
–>Central dyslexia: after visual word form area
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What is the standard dual-route model for reading aloud?
-Grapheme-phenome conversion route
-Lexical-semantic route
(image)
What is the grapheme-phoneme conversion route of the dual-route model for reading aloud?
-First converting each grapheme into phonemes
-Then to speech production system
What is the lexical-semantic route of the dual-route model for reading aloud?
-First accessing visual lexicon of existing words
-Then connecting words to semantic memory
-Then accessing phonological lexicon
-Then to speech production system
What kinds of conditions are associated with the dual-route model?
-Acquired surface dyslexia
-Acquired phonological dyslexia
-Acquired deep dyslexia
What is acquired surface dyslexia?
-Impaired lexical-semantic route, spared (reliance on) grapheme-phoneme conversion route
-Able to read regular words and non-words
-Unable to read irregular words: no lexicon to rely on
-Make regularization errors: pronouncing words as if regular
What is acquired phonological dyslexia?
-Impaired grapheme-phoneme conversion route, spared lexical-semantic route
-Able to read real words
-Unable/problems to read non-words: no lexicon available for non-words
-Often responding with similar real word instead
What is acquired deep dyslexia?
-Impaired grapheme-phoneme conversion route AND lexical-semantic route
-Problem with reading non-words more than words
-Real words also error prone, with semantic errors (ex: dog instead of cat)
What problems are there with the dual-route model?
-Some dyslexic patients can read irregular words they don’t understand
-Suggests semantic memory doesn’t work, but phonological lexicon does
-Alternative routes should bypass semantic memory
Which alternative route was suggested to add to the dual-route model?
Lexical-semantic route without semantic memory stage: summation hypothesis route (bypasses semantic memory)
(image)
What is the summation hypothesis route?
-Via grapheme-phoneme conversion stage to phonological lexicon
-Irregular word exists in phonological lexicon
-Bypasses semantic memory
-Alternative route
What is developmental dyslexia?
-Much more common than acquired dyslexia
-Problem in reading/spelling, not attributable to missed opportunity, brain injury or basic sensory deficits
-Visual and auditory explanations
–>Most dominant: phonological awareness (ability to segment speech stream into units)
-Heterogeneity, sometimes clear-cut developmental surface or phonological dyslexia
What has functional imaging revealed about existence of multiple routes?
-Confirm multiple routes: early processing of reading in virtual cortex, then either grapheme-phoneme conversion route or semantic memory route
-Grapheme-phoneme conversion route: from inferior parts of parietal cortex (supramarginal gyrus and angular gyrus) to inferior frontal gyrus (Broca’s area)
-Semantic memory route: from inferior temporal lobe to inferior frontal gyrus (Broca’s area)
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What are spelling and writing?
-Spelling: selecting and retrieving letter string, retrieved code may be abstract in that it isn’t tied to 1 modality of output
-Graphemic buffer: short-term memory component, maintains abstract letter identities during output processes
-Writing: translating abstract letter code into series of motor commands (pen strokes)
What is the dual-route model of spelling?
Spoken word => phonological buffer
-Phonological lexicon => semantic system => orthographic lexicon => graphemic buffer
–>Letter name conversion => phonological output buffer => speech/oral spelling
–>Allographic conversion => graphomotor patterns => writing
-Phoneme-grapheme conversion => graphemic buffer
–>Letter name conversion => phonological output buffer => speech/oral spelling
–>Allographic conversion => graphomotor patterns => writing
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What is the phoneme-grapheme conversion route of spelling according to the dual-route model of spelling?
-Converting each phoneme into graphemes
-Then to spelling production system
What is the lexical-semantic route of spelling according to the dual-route model of spelling?
-Accessing phonological lexicon
-Then connecting words to semantic memory
-Then accessing visual lexicon of existing words
-Then to spelling production system
What conditions can be caused by damage to the routes of spelling?
-Acquired surface dysgraphia
-Acquired phonological dysgraphia
-Acquired deep dysgraphia
What is acquired surface dysgraphia?
-Impaired lexical-semantic route, spared (and reliance on) phoneme-grapheme conversion route
-Problems with irregularly spelled words
-Regularization errors (ex: yacht as YOT)
-Able to spell non-words
What is acquired phonological dysgraphia?
-Impaired phoneme-grapheme conversion route, spared lexical-semantic route
-Able to spell real words
-Unable/problems with non-words
What is acquired deep dysgraphia?
-Impaired phoneme-grapheme conversion route AND semantic memory (lexical-semantic route)
-Able to spell real words, but more semantic errors (ex: dog instead of cat)
-Unable/problems with non-words
