psyc4080d learning disabilities 1. psyc4080d learning disabilities 2 a word on definitions… a...

PSYC4080DPSYC4080D Learning DisabilitiesLearning Disabilities 11

Learning DisabilitiesLearning Disabilities


A word on definitions…A word on definitions…

A “learning disability” (LD) is an A “learning disability” (LD) is an administrative termadministrative term

Each school board has it’s own Each school board has it’s own definition.definition.

In Ontario, there are In Ontario, there are 14 definitions of 14 definitions of LDsLDs boards, provincial an federal government boards, provincial an federal government

(Helps, 2000)(Helps, 2000) DSM-IV has 3 subtypes:DSM-IV has 3 subtypes:1.1. Reading DisorderReading Disorder2.2. Mathematics DisorderMathematics Disorder3.3. Disorder of Written ExpressionDisorder of Written Expression


PrevalencePrevalence

Different definitions makes it is hard to Different definitions makes it is hard to determine prevalencedetermine prevalence

Estimates range from 2 to 20% of the Estimates range from 2 to 20% of the population (Smith, 1994).population (Smith, 1994). Literature defines Specific Language Literature defines Specific Language Impairments (SLI) separately from dyslexiaImpairments (SLI) separately from dyslexia

1/2 of children in special needs classes 1/2 of children in special needs classes have a diagnosed LD.have a diagnosed LD.


Case StudyCase Study

When I’m in class, there’s not enough time to copy from 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 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 me a long time to check nearly every word to find my place. It’s really easy to get frustrated.place. It’s really easy to get frustrated.

When my teacher checks my work I have lots of When my teacher checks my work I have lots of mistakes.I don't like having to stay in to finish copying 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 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 always know what letter to write.I never know what I have written.I can't see the words on the whiteboard. have written.I can't see the words on the whiteboard. They can move around and sometimes I see two words They can move around and sometimes I see two words the same. the same.


Case StudyCase Study

I didn’t want to ask for help because I didn’t want people 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 to know I have a disability. I didn’t want people to think I was stupid.was stupid.

It was also hard when I was able to get a notetaker for 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 my classes. There were a few people who didn’t believe I had a problem and who said that I was lazy.had a problem and who said that I was lazy.


DSM-IV CriteriaDSM-IV Criteria

1.1. Reading DisorderReading Disorder

2.2. Mathematics DisorderMathematics Disorder

3.3. Disorder of Written ExpressionDisorder of Written Expression

A.A. Achievement in any of these areas, as Achievement in any of these areas, as measured by individually administered measured by individually administered standardized tests, is substantially standardized tests, is substantially below that expected given the person’s below that expected given the person’s chronological age, measured intelligence, chronological age, measured intelligence, and age-appropriate education.and age-appropriate education.


DSM-IV CriteriaDSM-IV Criteria

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

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


Pure AlexiaPure Alexia

Pure word blindnessPure word blindness• Affects vision, cannot read their own writingAffects vision, cannot read their own writing

Able to write (no Able to write (no agraphiaagraphia or other or other writing disability)writing disability)

Able to recognize words that are spelled Able to recognize words that are spelled aloud to them (auditory)aloud to them (auditory)

No No visual agnosiavisual agnosia (ability to recognize (ability to recognize objects)objects)


Alexia: PathologyAlexia: Pathology

Occipital lobe Occipital lobe lesionslesions

Preventing Preventing visual visual information information from reaching from reaching (left) (left) extrastriate extrastriate cortex cortex

Lesions to Lesions to posterior posterior corpus callosum corpus callosum


How do we read?How do we read?

At least two different processes:At least two different processes:

1.1. Phonetic (sound-based) reading Phonetic (sound-based) reading • unfamiliar words unfamiliar words • requires recognition of individual requires recognition of individual

symbolssymbols• sounds associated with letters and sounds associated with letters and

numbersnumbers

2. 2. Whole-word readingWhole-word reading• familiar word, we recognize it by its familiar word, we recognize it by its

shapeshape• context: context: “reading is predicting”“reading is predicting”


Model of the reading processModel of the reading process

VisualVisual

PerceptionPerception CognitionCognition

Whole Word Whole Word RecognitionRecognition

Phonetic Phonetic Word Word

RecognitionRecognition



VisualVisual



word word feature feature extractionextraction

word word recognitiorecognition, n, phonemic phonemic expressionexpression





VisualVisual



word word feature feature extractionextraction

word word recognitiorecognition, n, phonemic phonemic expressionexpression



letter letter feature feature extractionextraction

phoneme phoneme recognitiorecognition, n, expressionexpression


Whole word readingWhole word reading

Evidence comes from the study of Evidence comes from the study of dyslexias:dyslexias:

AcquiredAcquired: brain damage in those who : brain damage in those who already know how to readalready know how to read• Result of some trauma (tumour, stroke)Result of some trauma (tumour, stroke)

DevelopmentalDevelopmental: difficulties in children : difficulties in children learning to readlearning to read• Congenital illness or early childhood traumaCongenital illness or early childhood trauma


DyslexiasDyslexias

1. Surface Dyslexia1. Surface Dyslexia Deficit in whole word readingDeficit in whole word reading Errors related to visual appearance of Errors related to visual appearance of wordswords

Semantic understanding is normalSemantic understanding is normal They rely predominantly on phonetic They rely predominantly on phonetic reading for understandingreading for understanding

Cannot read irregular wordsCannot read irregular words


DyslexiasDyslexias

2. Phonological Dyslexia2. Phonological Dyslexia Are able to read familiar words using Are able to read familiar words using whole word methodwhole word method

Cannot linking letters to phonemesCannot linking letters to phonemes Trouble reading or learning unfamiliar Trouble reading or learning unfamiliar words or words or nonwordsnonwords


DyslexiasDyslexias

3. Word-form or spelling dyslexia3. Word-form or spelling dyslexia Cannot recognize whole words or sound them Cannot recognize whole words or sound them out phoneticallyout phonetically

Can recognize individual letters and can Can recognize individual letters and can read words if naming the letters one at a read words if naming the letters one at a timetime

Very slow readersVery slow readers Normal auditory recognition Normal auditory recognition

• Words spelt aloudWords spelt aloud• Word memory intactWord memory intact


DyslexiasDyslexias

4. Direct dyslexia4. Direct dyslexia Phonemic and whole word reading intactPhonemic and whole word reading intact

• Able to read aloud Able to read aloud

Semantic deficit: Cannot link words to Semantic deficit: Cannot link words to meaningmeaning• Cannot understand words they’re sayingCannot understand words they’re saying

Cannot match words with corresponding Cannot match words with corresponding picturespictures


DyslexiasDyslexias

5. Comprehension without reading5. Comprehension without reading Unable to read phonetically Unable to read phonetically Some comprehension of words they cannot Some comprehension of words they cannot readread

However, can match words they can’t read However, can match words they can’t read with pictureswith pictures


Dysgraphia: Writing DisordersDysgraphia: Writing Disorders

Two types:Two types:

1.1. Motor controlMotor control directing movements to form letters and directing movements to form letters and

wordswords

2. Various cognitive-based disorders2. Various cognitive-based disorders writing numbers but not letterswriting numbers but not letters writing uppercase but not lowercase writing uppercase but not lowercase

lettersletters Writing consonants but not vowelsWriting consonants but not vowels writing single letters but not wordswriting single letters but not words They have normal motor controlThey have normal motor control


How do we write?How do we write?

There are four possible ways:There are four possible ways:1. Phonetic1. Phonetic: Sound them out before writing: Sound them out before writing may do this with long, unfamiliar wordsmay do this with long, unfamiliar words2. 2. ImageryImagery: Transcribing an image of what a : Transcribing an image of what a

word looks likeword looks like visual image of word is kept in mind visual image of word is kept in mind

during writingduring writing3. 3. Serial memorySerial memory: Memorization of letter : Memorization of letter

sequencessequences memory of sequences of letters in a wordmemory of sequences of letters in a word4. 4. Motor memoryMotor memory: often repeated written : often repeated written

words (signature)words (signature)


DysgraphiasDysgraphias

1. Phonetic (phonological dysgraphia)1. Phonetic (phonological dysgraphia) Unable to sound out words and write them Unable to sound out words and write them phoneticallyphonetically

They cannot write unfamiliar words or They cannot write unfamiliar words or pronounceable nonwordspronounceable nonwords

Can visually image familiar words, then Can visually image familiar words, then write them (visual, not phonetic strategy) write them (visual, not phonetic strategy)

Caused by damage to the (left) superior Caused by damage to the (left) superior temporal lobetemporal lobe



2. Image-Based (orthographic dyslexia)2. Image-Based (orthographic dyslexia) Disorder of visually based writing Disorder of visually based writing Can only sound out familiar words Can only sound out familiar words Can write pronounceable nonsense wordsCan write pronounceable nonsense words Have difficulty spelling irregular wordsHave difficulty spelling irregular words



3. Serial Memory 3. Serial Memory memorizing sequences of letters that spell memorizing sequences of letters that spell particular words (I.e. spelling bee)particular words (I.e. spelling bee)

Cippolitti and Warrington (1996): patient Cippolitti and Warrington (1996): patient with a Left Hemisphere strokewith a Left Hemisphere stroke• Disrupted ability to spell words Disrupted ability to spell words • Impaired ability to recognize a word that Impaired ability to recognize a word that examiners would spell aloudexaminers would spell aloud



4. Pure Motor Memory (4. Pure Motor Memory (direct dysgraphia)direct dysgraphia) Can Write words that are dictated to them Can Write words that are dictated to them even thought they cannot understand these even thought they cannot understand these wordswords


NeuropathologyNeuropathology

1.1.Superior temporal lobe (Galaburda and Superior temporal lobe (Galaburda and colleagues, 1985-1990)colleagues, 1985-1990)

perisylvian cortex (surrounding syvian perisylvian cortex (surrounding syvian fissure) fissure)

abnormalities in part of Wernicke’s area abnormalities in part of Wernicke’s area called the planum temporale associated called the planum temporale associated with developmental dyslexiawith developmental dyslexia

left planum temporale is usually larger left planum temporale is usually larger in normal controlsin normal controls

in dyslexics they are both equal sizein dyslexics they are both equal size not all people with dyslexia show this anomalynot all people with dyslexia show this anomaly



2. Visual and auditory pathway abnormalities 2. Visual and auditory pathway abnormalities Magnocellular layer of LGN (thalamus) may Magnocellular layer of LGN (thalamus) may be damaged be damaged (Galaburda & Livingstone, 1993)(Galaburda & Livingstone, 1993)

• Motion and spatial locationMotion and spatial location

MGN damage in thalamus can cause MGN damage in thalamus can cause difficulties in hearingdifficulties in hearing

Dyslexics often have difficulties with Dyslexics often have difficulties with perception of letters and of movements in perception of letters and of movements in spacespace• Particularly with developmental dyslexiaParticularly with developmental dyslexia


What and Where PathwaysWhat and Where Pathways

Albright & Stoner, 2002



More on visual pathway deficits…More on visual pathway deficits… Transposition of letters is commom: moving Transposition of letters is commom: moving around, merging, and becoming blurryaround, merging, and becoming blurry

Maybe related to eye movements, since Maybe related to eye movements, since fixation is often unsteadyfixation is often unsteady

Motion sensitive areas of V5 in the Motion sensitive areas of V5 in the extrastriate cortex (posterior temporal extrastriate cortex (posterior temporal lobe) are not activated in persons with lobe) are not activated in persons with LDs to moving stimuliLDs to moving stimuli


EtiologyEtiology

1.1. Focal neuroanatomical abnormalitiesFocal neuroanatomical abnormalities Cell migration in perisylvian structuresCell migration in perisylvian structures

• Ectopias: abnormal positioningEctopias: abnormal positioning• Focal microgyri: small lesionsFocal microgyri: small lesions

Cytoarchitecture in thalamic nuclei Cytoarchitecture in thalamic nuclei • Disorganized, smaller cell bodies in Disorganized, smaller cell bodies in

magnocellular LGN and MGN neuronsmagnocellular LGN and MGN neurons

Genetic correlate of these abnormalities Genetic correlate of these abnormalities found in micefound in mice


EtiologyEtiology

2. Primary phonological deficits cause 2. Primary phonological deficits cause secondary sensory and motor deficitssecondary sensory and motor deficits

Perisylvian anomalies are primaryPerisylvian anomalies are primary Cortical lesions produce secondary Cortical lesions produce secondary

thalamic abnormalitiesthalamic abnormalities Affecting relay neurons to vision, audition, Affecting relay neurons to vision, audition,

motor centresmotor centres


Other InformationOther Information

• LD is a lifelong disorder.LD is a lifelong disorder.• Many people who have LDs may either Many people who have LDs may either compensate for their difficulties, or compensate for their difficulties, or avoid situations where their weaknesses avoid situations where their weaknesses are likely to show.are likely to show.

• More and more universities have special More and more universities have special services for those with LDs.services for those with LDs.

• Not so in the workplace – problems may go Not so in the workplace – problems may go unnoticed.unnoticed.

psyc4080d learning disabilities 1. psyc4080d learning disabilities 2 a word on definitions… a...

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