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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 l.jpg

Learning Disabilities

Learning Disabilities


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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


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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


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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


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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


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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


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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


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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


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Alexia: Pathology

  • Occipital lobe lesions

  • Preventing visual information from reaching (left) extrastriate cortex

  • Lesions to posterior corpus callosum

Learning Disabilities


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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


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Model of the reading process

Learning Disabilities


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Model of the reading process

Learning Disabilities


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Model of the reading process

Learning Disabilities


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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


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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


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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


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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


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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


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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


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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


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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


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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


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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


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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


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Dysgraphias

4. Pure Motor Memory (direct dysgraphia)

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

Learning Disabilities


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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



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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


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What and Where Pathways

Albright & Stoner, 2002

Learning Disabilities


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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


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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


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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


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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