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Learning Disabilities. A word on definitions…. A “learning disability” (LD) is an administrative term Each school board has it’s own definition. In Ontario, there are 14 definitions of LDs boards, provincial an federal government (Helps, 2000) DSM-IV has 3 subtypes: Reading Disorder

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learning disabilities

Learning Disabilities

Learning Disabilities

a word on definitions
A word on definitions…
  • A “learning disability” (LD) is an administrative term
  • Each school board has it’s own definition.
  • In Ontario, there are 14 definitions of LDs
    • boards, provincial an federal government (Helps, 2000)
  • DSM-IV has 3 subtypes:
  • Reading Disorder
  • Mathematics Disorder
  • Disorder of Written Expression

Learning Disabilities

prevalence
Prevalence
  • Different definitions makes it is hard to determine prevalence
  • Estimates range from 2 to 20% of the population (Smith, 1994).
    • Literature defines Specific Language Impairments (SLI) separately from dyslexia
  • 1/2 of children in special needs classes have a diagnosed LD.

Learning Disabilities

case study
Case Study
  • When I’m in class, there’s not enough time to copy from the board. I lose my place. I try hard but get lost. It takes me a long time to check nearly every word to find my place. It’s really easy to get frustrated.
  • When my teacher checks my work I have lots of mistakes.
I don\'t like having to stay in to finish copying from the board.
I can\'t read the joined up writing, I don\'t always know what letter to write.
I never know what I have written.
I can\'t see the words on the whiteboard. They can move around and sometimes I see two words the same.

Learning Disabilities

case study5
Case Study
  • I didn’t want to ask for help because I didn’t want people to know I have a disability. I didn’t want people to think I was stupid.
  • It was also hard when I was able to get a notetaker for my classes. There were a few people who didn’t believe I had a problem and who said that I was lazy.

Learning Disabilities

dsm iv criteria
DSM-IV Criteria
  • Reading Disorder
  • Mathematics Disorder
  • Disorder of Written Expression
  • Achievement in any of these areas, as measured by individually administered standardized tests, is substantially below that expected given the person’s chronological age, measured intelligence, and age-appropriate education.

Learning Disabilities

dsm iv criteria7
DSM-IV Criteria

B. The disturbance in Criterion A significantly interferes with academic achievement or activities of daily living that require the ability.

C. If a sensory deficit is present, the difficulties are in excess of those usually associated with it.

Learning Disabilities

pure alexia
Pure Alexia
  • Pure word blindness
    • Affects vision, cannot read their own writing
  • Able to write (no agraphia or other writing disability)
  • Able to recognize words that are spelled aloud to them (auditory)
  • No visual agnosia (ability to recognize objects)

Learning Disabilities

alexia pathology
Alexia: Pathology
  • Occipital lobe lesions
  • Preventing visual information from reaching (left) extrastriate cortex
  • Lesions to posterior corpus callosum

Learning Disabilities

how do we read
How do we read?

At least two different processes:

  • Phonetic (sound-based) reading
  • unfamiliar words
  • requires recognition of individual symbols
  • sounds associated with letters and numbers

2. Whole-word reading

  • familiar word, we recognize it by its shape
  • context: “reading is predicting”

Learning Disabilities

model of the reading process
Model of the reading process

Learning Disabilities

model of the reading process12
Model of the reading process

Learning Disabilities

model of the reading process13
Model of the reading process

Learning Disabilities

whole word reading
Whole word reading

Evidence comes from the study of dyslexias:

  • Acquired: brain damage in those who already know how to read
    • Result of some trauma (tumour, stroke)
  • Developmental: difficulties in children learning to read
    • Congenital illness or early childhood trauma

Learning Disabilities

dyslexias
Dyslexias

1. Surface Dyslexia

  • Deficit in whole word reading
  • Errors related to visual appearance of words
  • Semantic understanding is normal
  • They rely predominantly on phonetic reading for understanding
  • Cannot read irregular words

Learning Disabilities

dyslexias16
Dyslexias

2. Phonological Dyslexia

  • Are able to read familiar words using whole word method
  • Cannot linking letters to phonemes
  • Trouble reading or learning unfamiliar words or nonwords

Learning Disabilities

dyslexias17
Dyslexias

3. Word-form or spelling dyslexia

  • Cannot recognize whole words or sound them out phonetically
  • Can recognize individual letters and can read words if naming the letters one at a time
  • Very slow readers
  • Normal auditory recognition
    • Words spelt aloud
    • Word memory intact

Learning Disabilities

dyslexias18
Dyslexias

4. Direct dyslexia

  • Phonemic and whole word reading intact
    • Able to read aloud
  • Semantic deficit: Cannot link words to meaning
    • Cannot understand words they’re saying
  • Cannot match words with corresponding pictures

Learning Disabilities

dyslexias19
Dyslexias

5. Comprehension without reading

  • Unable to read phonetically
  • Some comprehension of words they cannot read
  • However, can match words they can’t read with pictures

Learning Disabilities

dysgraphia writing disorders
Dysgraphia: Writing Disorders

Two types:

  • Motor control
  • directing movements to form letters and words

2. Various cognitive-based disorders

  • writing numbers but not letters
  • writing uppercase but not lowercase letters
  • Writing consonants but not vowels
  • writing single letters but not words
  • They have normal motor control

Learning Disabilities

how do we write
How do we write?
  • There are four possible ways:

1. Phonetic: Sound them out before writing

  • may do this with long, unfamiliar words

2. Imagery: Transcribing an image of what a word looks like

  • visual image of word is kept in mind during writing

3. Serial memory: Memorization of letter sequences

  • memory of sequences of letters in a word

4. Motor memory: often repeated written words (signature)

Learning Disabilities

dysgraphias
Dysgraphias

1. Phonetic (phonological dysgraphia)

  • Unable to sound out words and write them phonetically
  • They cannot write unfamiliar words or pronounceable nonwords
  • Can visually image familiar words, then write them (visual, not phonetic strategy)
  • Caused by damage to the (left) superior temporal lobe

Learning Disabilities

dysgraphias23
Dysgraphias

2. Image-Based (orthographic dyslexia)

  • Disorder of visually based writing
  • Can only sound out familiar words
  • Can write pronounceable nonsense words
  • Have difficulty spelling irregular words

Learning Disabilities

dysgraphias24
Dysgraphias

3. Serial Memory

  • memorizing sequences of letters that spell particular words (I.e. spelling bee)
  • Cippolitti and Warrington (1996): patient with a Left Hemisphere stroke
    • Disrupted ability to spell words
    • Impaired ability to recognize a word that examiners would spell aloud

Learning Disabilities

dysgraphias25
Dysgraphias

4. Pure Motor Memory (direct dysgraphia)

  • Can Write words that are dictated to them even thought they cannot understand these words

Learning Disabilities

neuropathology
Neuropathology
  • Superior temporal lobe (Galaburda and colleagues, 1985-1990)
  • perisylvian cortex (surrounding syvian fissure)
  • abnormalities in part of Wernicke’s area called the planum temporale associated with developmental dyslexia
  • left planum temporale is usually larger in normal controls
  • in dyslexics they are both equal size
    • not all people with dyslexia show this anomaly

Learning Disabilities

neuropathology28
Neuropathology

2. Visual and auditory pathway abnormalities

  • Magnocellular layer of LGN (thalamus) may be damaged (Galaburda & Livingstone, 1993)
    • Motion and spatial location
  • MGN damage in thalamus can cause difficulties in hearing
  • Dyslexics often have difficulties with perception of letters and of movements in space
    • Particularly with developmental dyslexia

Learning Disabilities

what and where pathways
What and Where Pathways

Albright & Stoner, 2002

Learning Disabilities

neuropathology30
Neuropathology

More on visual pathway deficits…

  • Transposition of letters is commom: moving around, merging, and becoming blurry
  • Maybe related to eye movements, since fixation is often unsteady
  • Motion sensitive areas of V5 in the extrastriate cortex (posterior temporal lobe) are not activated in persons with LDs to moving stimuli

Learning Disabilities

etiology
Etiology
  • Focal neuroanatomical abnormalities
  • Cell migration in perisylvian structures
    • Ectopias: abnormal positioning
    • Focal microgyri: small lesions
  • Cytoarchitecture in thalamic nuclei
    • Disorganized, smaller cell bodies in magnocellular LGN and MGN neurons
  • Genetic correlate of these abnormalities found in mice

Learning Disabilities

etiology32
Etiology

2. Primary phonological deficits cause secondary sensory and motor deficits

  • Perisylvian anomalies are primary
  • Cortical lesions produce secondary thalamic abnormalities
    • Affecting relay neurons to vision, audition, motor centres

Learning Disabilities

other information
Other Information
  • LD is a lifelong disorder.
  • Many people who have LDs may either compensate for their difficulties, or avoid situations where their weaknesses are likely to show.
  • More and more universities have special services for those with LDs.
  • Not so in the workplace – problems may go unnoticed.

Learning Disabilities

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