Transcript PPT
Learning Disabilities PSYC4080D Learning Disabilities 1 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 1. 2. 3. boards, provincial an federal government (Helps, 2000) DSM-IV has 3 subtypes: Reading Disorder Mathematics Disorder Disorder of Written Expression PSYC4080D Learning Disabilities 2 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. PSYC4080D Learning Disabilities 3 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. PSYC4080D Learning Disabilities 4 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. PSYC4080D Learning Disabilities 5 DSM-IV Criteria 1. Reading Disorder 2. Mathematics Disorder 3. Disorder of Written Expression A. 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. PSYC4080D Learning Disabilities 6 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. PSYC4080D Learning Disabilities 7 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) PSYC4080D Learning Disabilities 8 Alexia: Pathology Occipital lobe lesions Preventing visual information from reaching (left) extrastriate cortex Lesions to posterior corpus callosum PSYC4080D Learning Disabilities 9 How do we read? At 1. • • • 2. • • least two different processes: Phonetic (sound-based) reading unfamiliar words requires recognition of individual symbols sounds associated with letters and numbers Whole-word reading familiar word, we recognize it by its shape context: “reading is predicting” PSYC4080D Learning Disabilities 10 Model of the reading process Visual Perception Cognition Whole Word Recognition Phonetic Word Recognition PSYC4080D Learning Disabilities 11 Model of the reading process Visual Perception Whole Word word Recognition feature extraction Cognition word recognition, phonemic expression Phonetic Word Recognition PSYC4080D Learning Disabilities 12 Model of the reading process Visual Perception Cognition Whole Word word Recognition feature extraction word recognition, phonemic expression Phonetic letter Word feature Recognition extraction phoneme recognition, expression PSYC4080D Learning Disabilities 13 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 PSYC4080D Learning Disabilities 14 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 PSYC4080D Learning Disabilities 15 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 PSYC4080D Learning Disabilities 16 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 PSYC4080D Learning Disabilities 17 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 PSYC4080D Learning Disabilities 18 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 PSYC4080D Learning Disabilities 19 Dysgraphia: Writing Disorders 1. 2. Two types: Motor control directing movements to form letters and words 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 PSYC4080D Learning Disabilities 20 How do we write? 1. 2. 3. 4. There are four possible ways: Phonetic: Sound them out before writing may do this with long, unfamiliar words Imagery: Transcribing an image of what a word looks like visual image of word is kept in mind during writing Serial memory: Memorization of letter sequences memory of sequences of letters in a word Motor memory: often repeated written words (signature) PSYC4080D Learning Disabilities 21 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 PSYC4080D Learning Disabilities 22 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 PSYC4080D Learning Disabilities 23 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 PSYC4080D Learning Disabilities 24 Dysgraphias 4. Pure Motor Memory (direct dysgraphia) Can Write words that are dictated to them even thought they cannot understand these words PSYC4080D Learning Disabilities 25 Neuropathology 1. 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 PSYC4080D Learning Disabilities 26 PSYC4080D Learning Disabilities 27 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 PSYC4080D Learning Disabilities 28 What and Where Pathways Albright & Stoner, 2002 PSYC4080D Learning Disabilities 29 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 PSYC4080D Learning Disabilities 30 Etiology 1. 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 PSYC4080D Learning Disabilities 31 Etiology 2. Primary phonological deficits cause secondary sensory and motor deficits Perisylvian anomalies are primary Cortical lesions produce secondary thalamic abnormalities PSYC4080D Affecting relay neurons to vision, audition, motor centres Learning Disabilities 32 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. PSYC4080D Learning Disabilities 33