Text of Outline David Wechsler – some history Wechsler’s Scales IQ scores Index scores Verbal subtests...
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Outline David Wechsler some history Wechslers Scales IQ scores Index scores Verbal subtests Performance subtests WAIS Psychometrics
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David Wechsler (1896 1981) Studied at Columbia University (M.A., 1917; Ph.D., 1925) Went to France with US Army in 1919, then to London Studied with Pearson & Spearman Also with Anna Freud in Vienna
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David Wechsler Worked at NYs Bellevue Hospital. Unhappy with the Stanford-Binet Content appropriate only for children Rapport problems if used with adults Produces only a single score Norms not appropriate for adults Binets emphasis on speed hurt older adults scores
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Wechsler Scales 1939: the Wechsler-Bellevue, later called the WAIS. 1945: the Wechsler Memory Scale 1949: the childrens version, the WISC 1955: Wechsler Adult Intelligence Scale 1967: the WPPSI for children ages 2 -7 1981: WAIS-R (revised form of 1955 test) 1997: WAIS-III
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Wechsler Scales Intelligence is the aggregate or global capacity of the individual to act purposefully, to think rationally and to deal effectively with his environment. David Wechsler (1939) global: one score ultimately describes a persons intellectual ability aggregate: that one score is composed of a number of sub-scores
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Wechslers original test Wechsler believed that intellectual ability involves two major types of skills: verbal and performance abilities. Each of these broad types includes a variety of specific skills that are assessed by the various subtests of the WAIS. However, all these subtests measure g as well as specific skills
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Full Scale IQ Verbal IQPerformance IQ VCIWMIPOIPSI Vocabulary Similarities Information Comprehension Digit Span Arithmetic Letter-Number Sequencing Block Design Matrix reasoning Picture completion Picture arrangement Digit-Symbol Coding Symbol Search
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Wechsler test produced 3 IQ scores Full-scale IQ: reflects both verbal and performance IQs most reliable and valid score extracted from WAIS why do you think this is the most reliable?
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Wechsler test produced 3 IQ scores Verbal IQ: Responses require person being tested to use language to understand instructions or to make a response
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Wechsler test produced 3 IQ scores Performance IQ: Performance subtests involve doing something, not just answering questions
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Structure of the WAIS WAIS-III has four index scores: verbal comprehension working memory perceptual organization processing speed. Index scores added recently because, with new subtests, factor analysis suggests these four factors
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Index scores Verbal comprehension assesses general verbal skills, such as verbal fluency, ability to understand and use verbal reasoning, and verbal knowledge based on both formal and informal educational opportunities,
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Index scores Working memory The blackboard of the mind (Goldman-Rakic, 1992) Encode information into STM, store it there, retrieve it when needed Manipulate information (e.g., addition) Thinking, learning, planning
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Index scores Perceptual organization Use visual, spatial, and visually-guided motor skills Organize thoughts Assesses comfort with new, unfamiliar situations
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Index score Processing speed The speed at which cognitive processes can be carried out focus, scanning speed, sequentially ordering visual information sensitive to motivation, difficulty working under time pressure. biological cultural factors have little impact
Vocabulary Subject is given one word at a time, asked to define it Sensitive to word knowledge, linguistic development, acquired knowledge, verbal expression ability, crystallized intelligence The best single measure of g Correlation of vocabulary score with g is.83
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Vocabulary Very stable Resistant to effects of poor concentration in schizophrenia Not affected by mild concentration trouble Of all WAIS subtests, the one most resistant to brain damage Thus, allows a good estimate of pre-morbid functioning
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Similarities Task is to say how two (superficially) dissimilar items might be similar Evaluating details which details are diagnostic? Earlier items in series are known through experience (e.g., In what way are a cake and a pudding alike?) Later items require abstract thinking (e.g., How are affection and approval alike?
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Similarities Logical, abstract thinking Concept formation Crystallized and fluid intelligence With Information subtest, the second best for measuring g Correlation with g =.79
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Similarities Of VCI (Verbal Comprehension Index) subtests, the one least affected by formal education or learning Score on this subtest is impacted by psychopathology, and by brain damage esp. left hemisphere lesions
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Arithmetic Assesses working memory, numerical reasoning, computation skill, concentration, retrieval from LTM Influenced by emotional state Correlation with g is r =.75
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Digit Span Repeat a series of up to 7 digits in correct order Digits presented 1 per second Tested both Forward (DSF) and Backward (DSB) Attention, auditory memory and sequencing, short term memory, mental alertness, sequential processing, cognitive flexibility
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Digit Span Average 6.4 digits forward, 4.7 backwards DSF DSB 5 suggests brain damage Correlation with g: r=.57 (the worst)
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Information Acquired knowledge, crystallized intelligence, fund of information, range of general factual knowledge, long term memory Affected by formal education opportunities Correlation with g: r =.79 (2nd best) Failure on easy items followed by success on harder items suggests retrieval difficulties Resistant to psychopathology and brain damage good estimate of pre-morbid functioning
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Comprehension 3 different kinds of questions: Appropriate responses to hypothetical situations Logical explanations for everyday actions Proverb interpretations Assesses social and moral reasoning, judgment, verbal concepts, knowledge of ordinary standards of behavior, practical information
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Comprehension Rewards conventional responses, not creative ones R Hem patients may score high (their L Hem intact so they know answers) but still behave inappropriately g: correlation r =.77
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Letter-number sequencing Optional not needed to compute IQ Task is to re-order intermixed, randomly- sequenced numbers and letters Taps STM, sequential reasoning ability, planning g: correlation r =.65 Impaired by anxiety, weak attention focusing ability Dropping a letter: attention problem Mixing up letters: sequencing problem
Picture Completion Task: say what detail is missing from a picture. Timed response Pointing response is allowed Raises issue of pointing precision (trained examiner required) Alertness, attention to detail LTM (Visual) Crystallized intelligence R Hem skill g: correlation r =.64
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Digit Symbol Coding 1 X 2 39 8 9 1 6 3
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Visual STM Psychomotor speed Visual-motor coordination Visual sequencing Accuracy & speed g: correlation r =.59 Very sensitive to any kind of brain damage
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Block Design Assesses visual-motor coordination, visual analysis & synthesis, spatial visualization Visual input, motor output Fluid intelligence Trial & error learning g: correlation =.72 Affected by R Hem damage Bizarre solutions may indicate dementia
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Matrix Reasoning 4 types of stimuli: pattern completion classification analogy serial reasoning Subject given a series of matrices and must say what goes in the empty cell ?
Picture Arrangement Task is to put a series of (randomly-ordered) pictures into narrative order (so they tell a coherent story) As if you found a comic strip jumbled up and had to order the frames sensibly Non-verbal reasoning Possibly social skill Fluid & crystallized intelligence Planning Time concepts
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Picture Arrangement Failure may be due to visual problems (compare with Picture Completion) g: correlation r =.66
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Symbol Search Optional not needed to compute IQ Subject shown two target abstract symbols and asked whether either target appears in a set of probe symbols 120 seconds allowed How many can subject do in that time?
