Learning Disabilities

Learning Disabilities 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 • Mathematics Disorder • Disorder of Written Expression Learning Disabilities

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 • 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 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 • 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 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 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 • Occipital lobe lesions • Preventing visual information from reaching (left) extrastriate cortex • Lesions to posterior corpus callosum Learning Disabilities

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 Learning Disabilities

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 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

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

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

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

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 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? • 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 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

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

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

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 • 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

Learning Disabilities

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 Albright & Stoner, 2002 Learning Disabilities

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 • 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

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 • 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

Learning Disabilities