Neuropsychology: The Literate Brain

Question 1

What is reading as a learned expert system?

Answer 1

-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)

Question 2

What are the cognitive mechanisms for visual word recognition?

Answer 2

-Series of processing stages: starting with general visual processes
-Evidence for top-down effects in visual processing
(image)

Question 3

Which hierarchical processing stages are involved in reading?

Answer 3

-Detection for visual features
-Letter recognition
-Visual word recognition
-Meaning (semantics)

Question 4

How is feedback (top-down) used in visual processing?

Answer 4

-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

Question 5

How is the visual word form area (VWFA) a neural mechanism for reading?

Answer 5

Responds to written words more than consonant strings or false fonts (irrespective of which part of space they are displayed in)

Question 6

What are other characteristics of the visual word form area?

Answer 6

-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)

Question 7

What are the neural mechanisms for visual word recognition?

Answer 7

-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

Question 8

What does the underlying functional organization look like of reading?

Answer 8

Complex: not just 1 region
(image)

Question 9

What is pure alexia?

Answer 9

-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
(image)

Question 10

What is the standard dual-route model for reading aloud?

Answer 10

-Grapheme-phenome conversion route
-Lexical-semantic route
(image)

Question 11

What is the grapheme-phoneme conversion route of the dual-route model for reading aloud?

Answer 11

-First converting each grapheme into phonemes
-Then to speech production system

Question 12

What is the lexical-semantic route of the dual-route model for reading aloud?

Answer 12

-First accessing visual lexicon of existing words
-Then connecting words to semantic memory
-Then accessing phonological lexicon
-Then to speech production system

Question 13

What kinds of conditions are associated with the dual-route model?

Answer 13

-Acquired surface dyslexia
-Acquired phonological dyslexia
-Acquired deep dyslexia

Question 14

What is acquired surface dyslexia?

Answer 14

-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

Question 15

What is acquired phonological dyslexia?

Answer 15

-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

Question 16

What is acquired deep dyslexia?

Answer 16

-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)

Question 17

What problems are there with the dual-route model?

Answer 17

-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

Question 18

Which alternative route was suggested to add to the dual-route model?

Answer 18

Lexical-semantic route without semantic memory stage: summation hypothesis route (bypasses semantic memory)
(image)

Question 19

What is the summation hypothesis route?

Answer 19

-Via grapheme-phoneme conversion stage to phonological lexicon
-Irregular word exists in phonological lexicon
-Bypasses semantic memory
-Alternative route

Question 20

What is developmental dyslexia?

Answer 20

-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

Question 21

What has functional imaging revealed about existence of multiple routes?

Answer 21

-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)
(image)

Question 22

What are spelling and writing?

Answer 22

-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)

Question 23

What is the dual-route model of spelling?

Answer 23

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
(image)

Question 24

What is the phoneme-grapheme conversion route of spelling according to the dual-route model of spelling?

Answer 24

-Converting each phoneme into graphemes
-Then to spelling production system

Question 25

What is the lexical-semantic route of spelling according to the dual-route model of spelling?

Answer 25

-Accessing phonological lexicon
-Then connecting words to semantic memory
-Then accessing visual lexicon of existing words
-Then to spelling production system

Question 26

What conditions can be caused by damage to the routes of spelling?

Answer 26

-Acquired surface dysgraphia
-Acquired phonological dysgraphia
-Acquired deep dysgraphia

Question 27

What is acquired surface dysgraphia?

Answer 27

-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

Question 28

What is acquired phonological dysgraphia?

Answer 28

-Impaired phoneme-grapheme conversion route, spared lexical-semantic route
-Able to spell real words
-Unable/problems with non-words

Question 29

What is acquired deep dysgraphia?

Answer 29

-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