Reading and Dyslexia

• We can recognise written words very rapidly and accurately, in a series of fixations (averaging ~200ms) and saccades, with some words skipped altogether.
• Word Superiority Effect


  • Visual processing time is not strongly affected by length, suggesting letters are not analysed one by one
  • Letter identification is affected by whether it makes up a word or not
  • Letter identification has top-down influences from word knowledge
  • When word form is lost, you develop 'word blindness'
• Monsieur C developed 'Word Blindness' - incapable of understanding written words
• Autopsy by neurologist Joseph Dejerine shows stroke damage to the left ventral occipito-temporal cortex (vOTC)
• Dejerine thought this was a connection that carried visual information forward to language areas of the brain
• Others think this could be a 'mental dictionary' that stores the word forms
• Patients with left vOTC damage (dubbed the Visual Word Form Area) shows the word length effect, compared to visual cortex-lesioned patients without vOTC damage
• 1. vOTC is likely more than a mere visual connection, but an area that processes word forms
• Visual information is processed contralaterally: Left hemifield -> Right brain, Right hemifield -> Left brain
• Words shown in both hemifields activate the VWFA more than consonant strings
• Only the left vOTC seems to be specialised for word form processing
• In split-brain patients, the two hemispheres cannot talk, so visual information in the right visual cortex cannot be sent across to the left vOTC for word form processing
• The left vOTC may not be a 'visual lexicon' as such, but is probably specialised in processing particular kinds of stimuli that happen to be very important in reading.
• Visual word recognition is holistic, not letter-by-letter
• The word superiority effect shows that word knowledge influences letter identification
• The left vOTC is regarded the 'Visual Word Form Area'
• VWFA damage leads to pure alexia
• The VWFA is located on the left only
• The VWFA responds to other types of tasks such as naming, decision making and reading Braille
• The visual lexicon is debatable but top-down processes in visual word recognition is unequivocal
• A Basic Model for Reading Aloud

  1. Visual Word Form

  2. Access Pronunciation

  3. Read It Aloud
• Stroke patients with dyslexia reveal the intricate reading network in the brain
• Peripheral dyslexia


  Disruption of early visuo-attentional processing (letter & words)
• Central dyslexia


  Disruption of phonological or semantic processing after visual word form processing
• In pure alexia, reading is letter-by-letter and they struggle with abstract letter identity
• Attentional dyslexia involves difficulty in separating constituent letters/words and letter migration errors
• Neglect dyslexia involves letter substitution errors on one side (contralateral lesion) due to a spatial reference deficit and low-level visual features
• A Model for Reading Aloud

  1. Visual Word Form

  2. Access Pronunciation

  3. Read It Aloud

  4. Visual features & letters

  5. Visuo-spatial attention

  6. Peripheral Dyslexia

  7. Central Dyslexia

  8. Attentional dyslexia

  9. Neglect dyslexia

  10. Pure alexia
• Surface dyslexia patients know the rules of regular pronunciation, but when the pronunciation is irregular, they follow the regular pronunciation
• Surface dyslexia patients are OK reading nonwords and low-frequency words, suggesting a need for rule-based regular pronunciation and pronunciations stored holistically
• A Model for Reading Aloud

  1. Visual Word Form

  2. Access Pronunciation

  3. Read It Aloud

  4. Visual features & letters

  5. Visuo-spatial attention

  6. Peripheral Dyslexia

  7. Central Dyslexia

  8. Phonological lexicon

  9. Grapheme-to-Phoneme Conversion

  10. Attentional dyslexia

  11. Neglect dyslexia

  12. Pure alexia

  13. Surface dyslexia
• Phonological dyslexia patients can't pronounce non-words
• Visual Word Form


  Read It Aloud Access Pronunciation
• A Model for Reading Aloud

  • Visual features & letters
  • Visuo-spatial attention
  • Peripheral Dyslexia
  • Central Dyslexia
  • Phonological lexicon
  • Grapheme-to-Phoneme Conversion
  • Attentional dyslexia
  • Neglect dyslexia
  • Pure alexia
  • Surface dyslexia
  • Phonological dyslexia
  • Semantic memory
  • Deep dyslexia
• Surface Dyslexia


  Patients can't pronounce irregular words like PINT, they follow the regular pronunciation
• Phonological Dyslexia


  Patients are fine with real words (regular and irregular) but tend to read a nonword as a real word, they show problems in phonological processing
• Deep Dyslexia


  Patients read real words with semantic errors, derivational errors, read concrete words better than abstract words, phonological retrieval is affected by semantic impairment
• The Dual-Route Model of Reading Aloud

  • Lexico-Semantic Route
  • Phonological Route
• Mapping the Dual-Route Model in the Brain


  Resemblance to the speech network
• Summary of Dyslexia Types

  • Pure alexia
  • Attentional dyslexia
  • Neglect dyslexia
  • Surface dyslexia
  • Phonological dyslexia
  • Deep dyslexia