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Reading Disabilities

(11-7-13)

Specific reading disability (dyslexia)

  • Much interest has focused on reading difficulties in children with at least average intelligence and without “extraneous factors” accounting for their learning problems (sensory acuity deficits, socioeconomic disadvantage, severe emotional-behavioral disorders)–“exclusionary criteria”
    • They tend to have difficulties in learning basic reading subskills
      • word identification
      • phonological (letter-sound) decoding
  • Vellutino, Fletcher, Snowling, & Scanion (2004) estimate that 10% to 15% of school age children have such problems

Reading: “extracting and constructing meaning from written text for some purpose” (Vellutino et al., p. 5)

  • word identification: learning to decode print
  • phonological awareness: recognition that spoken words are built of individual speech sounds (phonemes) and combinations of these sounds (syllables)
    • phonological coding: using speech codes to represent information in the form of words and parts of words
      • problem with phonological memory
    • phonological analysis and alphabetic mapping
    • orthographic awareness: how letters in written words are organized
      • poor readers are usually (not always) poor spellers
  • deficits in general learning abilities have not been supported in terms of explaining dyslexia
    • Intelligence and reading
  • deficits in visual perception and visual memory have not been supported in terms of explaining dyslexia
    • continuing issues and questions
  • These results primarily pertain to languages such as English
    • English is described as having an opaque (deep) orthography: many inconsistencies and exceptions in the relationships between letters and sounds
    • other languages (e.g., German or Italian) show transparent (shallow) orthographies: more consistent mapping between letters and sounds
    • rhyming skills predicts reading achievement in English but not German or Dutch (where rapid naming accounts for more variance in reading ability)
    • reading in non-alphabetic languages (Chinese, Japanese) may be associated with multiple deficits, rather than a core phonological deficit

Etiological variables

  • Neurobiological factors: possible constitutional factors intrinsic to the child
    • brain structure: left hemisphere
    • brain function: left hemisphere
    • genetics
      • parental history of reading difficulties increases risk of dyslexia approximately 8 times
      • various reports find 25%-60% of parents of children showing dyslexia having reading problems
      • concordance rates for identical twins typically greater than 80% for monozygotic twins and below 50% for dizygotic twins
      • approximately 50-60% of the variance in reading achievement can be accounted for by genetic factors
        • chromosome 6, 15, 1, 2
        • genes:
          • DCDC2 on chromosome 6 has been found to be highly expressed in brain regions used during times of reading, affects neuron migration during development in fetal rats, and about 17% of dyslexics are missing a short stretch of DNA within DCDC2–everyone with this deleltion had dyslexia (Science, 2005, v. 310, p. 759); but, Monaco & Williams failed to find association between DCDC2 and dyslexia in their British population samples.
          • ROBO1 on chromosome 3 has been linked to dyslexia: reduced ROBO1 activity in 21 dyslexic individuals from large Finnish family, fruit fly version helps shape neural connections between two hemispheres of brain (Science, 2005, v. 310, p. 759)
          • KIAA0319, a third candidate dyslexia gene, may play role in brain development (Science, 2005, v. 310, p. 759)
      • environmental interaction
        • risk for dyslexia appears to be best conceptualized as “continuous”, rather an “all or none”
  • Environmental factors
    • pre-reading experience
    • inadequate instruction
      • Most consistently demonstrated remedial factor has been the amount of instruction in skill area

The method of identification of “dyslexic children”, “poor readers”, “children with specific reading disabilities” strongly influences the obtained sample and characteristics thereof

  • Skill discrepancy
  • Ability discrepancy
  • Statistical discrepancy
  • Response to experimental curriculum

Population

  • Prevalence: Reading problems are the most commonly identified learning disabilities in school age children
  • Sex Ration: More males than females are identified in most reports
  • Course: Varies most clearly with severity
    • milder cases may “disappear” for formal identification
    • severe cases appear to be more stable
  • Correlates:
    • Family histories of academic difficulties
    • Histories of early speech problems
    • Histories of early ear infections
    • Phonological processing difficulties
  • Comorbidity: often associated with other problems
    • ADD/ADHD
    • At least part of the comorbidity of Reading Disorder and ADHD appears related to pleiotropic effects of a quantitative trait locus (QTL) on chromosome 6p
      • producing more than one genetic effect; specifically : having multiple phenotypic expressions
    • behavior problems (ODD/Conduct Disorder)
    • substance use/abuse

Subtyping: highly controversal

Instruction

Five essential elements of reading instruction identified in The No Child Left Behind Act

  1. phonemic awareness
  2. phonics
  3. vocabulary development
  4. reading fluency, including oral reading skills
  5. reading-comprehension strategies

Definition of reading in No Child Left Behind Act

“reading” refers to a complex act of deriving meaning from print that requires the following:

  1. understanding how phonemes (speech sounds) are connected to print symbols
  2. an abilty to decode unfamiliar words
  3. an ability to read fluently
  4. adequate background knowledge and vocabulary to support reading comprehension
  5. development of effective, active strategies to construct meaning from print
  6. development and maintenance of motivation to read

Subtyping of reading disorders

(2-20-12)

Language pattern of Reading Disability

  • “phonological-deficit hypothesis” (Shaywitz, 1998)
  • “dysphonetic dyslexia” (Boder, 1973), “auditory-linguistic dyslexia” (Pirozzolo, 1979), “language pattern reading disorder”
  • The primary cause of reading problems is a core deficit in phonological processing. Phonological awareness is the ability to use the phonetic segments of speech, including awareness of and use of the sound structure of language. “Phonologically based reading disabilities” show high heritability estimates, weakness on a variety of verbal measure, attentional deficits, a high comorbidity with ADHD (Teeter & Semrud-Clikeman, 1997). There is often an early (and resolved by later ages) report of speech and/or language delays or deficits. There may be a history of early ear infections. There is often a family history of learning problems, especially reading problems. Spelling errors are usually phonetically inaccurate–poor “sound-symbol association.”
  • Relatively poor Verbal IQ scores, mispronounciations in oral reading, poor scores on auditory discrimination and word finding tests (Barkley, 1981).
  • most common, possibly at least 60-80% of identified cases
  • A recent review suggests that: “inadequate facility in word identification due, in most cases, to more basic deficits in alphabetic coding is the basic cuase of difficulties in learning to read.” (Vullution, Fletcher, Snowling, & Scanlon, 2004, p. 2).

Visual-spatial pattern (enduring perceptual-motor difficulties)

  • difficulty “revisualizing a word”; associated with problems in drawing, copying, constructional activities. Spelling errors are usually phonetically accurate but too many or too few letters may be used–the “shape” of the word is obviously wrong. “visual-orthographic deficits in reading” (Teeter & Semrud-Clikeman, 1997)
  • “dyseidetic dyslexia” (Boder, 1979), “visual-spatial dyslexia” (Pirozzolo, 1979)
  • minority pattern, possibly 5-15% of identified cases, may be more common at younger ages
  • Do poorly on tests of visual-spatial construction: drawing, copying; relatively low on Performance IQ tests; poor sight readers of words, make phonetically accurate spelling errors (Barkley, 1981).

Mixed pattern

  • rare, possibly 3-5%–10-20% of identified cases
  • “mixed dyslexia” (Boder, 1979)
  • Show little discrepancy between VIQ and PIQ, poor articulation, handwriting, and recall of sequences (Barkley, 1981)
  • may be at greatest risk to evolve into “hard core illiterate” population as adults

“Normal” LD pattern

  • group without identified psychological or neuropsychological deficit
  • rare, but has consistently been found in several studies
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