THE WECHSLER SCALES OF INTELLIGENCE IN PSYCHOLOGY
Wechsler consistently defined intelligence as "the aggregate or global capacity of the individual to act purposefully, to think rationally and to deal effectively with his environment" (Wechsler, 1958, p. 7).
He also emphasized that intelligence involved more than intellectual ability, although "the capacity to do intellectual work is a necessary and important sign of general intelligence" (Wechsler, 1958, p. 12). General intelligence or, more precisely, intelligent behavior depends on such variables as "persistence, drive, energy lew!, etc." (Wechsler, 1949, p. 5).
Beginning in the 1930s, David Wechsler, a psychologist at Bellevue Hospital in New York City, conceived a series of elegantly simple instruments that virtually defined intelligence testing in the mid- to late twentieth century.
Origins of the Wechsler Tests:
Wechsler began work on his first test in 1932, seeking to devise an instrument suitable for testing the diverse patients referred to the psychiatric section of Bellevue Hospital in New York (Wechsler, 1932). In describing the development of his first test, he later wrote, “Our aim was not to produce a set of brand new tests but to select, from whatever source available, such a combination of them as would meet the requirements of an effective adult scale” (Wechsler, 1939).
Wechsler was not so much a creative talent as a pragmatist who fashioned a new and useful instrument from the spare parts of earlier, discontinued attempts at intelligence testing.
Related Topics:
Related Topics:
The first of the Wechsler tests, named the Wechsler-Bellevue Intelligence Scales, was published in 1939.
Wechsler (1941) explained that existing instruments such as the Stanford-Binet were woefully inadequate for assessing adult intelligence. The Wechsler Bellevue was designed to rectify several flaws noted in previous tests:
--- The test items possessed no appeal for adults.
---Too many questions emphasized mere manipulation of words.
---The instructions emphasized speed at the expense of accuracy.
---The instructions emphasized speed at the expense of accuracy.
---The reliance on mental age was irrelevant to adult testing.
Wechsler designed his test specifically for adults, added performance items to balance verbal questions, reduced the emphasis upon speeded questions, and invented a new method for obtaining the IQ. Specifically, he replaced the usual formula.
This new formula was based on the interesting presumption —stated in the form of an axiom—that IQ remains constant with normal aging, even though raw intellectual ability might shift or even decline. The assumption of IQ constancy is basic to the Wechsler scales. As Wechsler (1941) put it:---
The constancy of the I.Q. is the basic assumption of all scales where relative degrees of intelligence are defined in terms of it. It is not only basic, but absolutely necessary that
I.Q.’s be independent of the age at which they are calculated, because unless the assumption holds, no permanent scheme of intelligence classification is possible.
I.Q.’s be independent of the age at which they are calculated, because unless the assumption holds, no permanent scheme of intelligence classification is possible.
Wechsler also hoped to use his test as an aid in psychiatric diagnosis. In pursuit of this goal, he divided his scale into separate verbal and performance sections. This division allowed the examiner to compare an examinee’s facility in using words and symbols (verbal subtests) versus the ability to manipulate objects and perceive visual patterns (performance subtests). Large differences between verbal ability (V) and performance ability (P) were thought to be of diagnostic significance. Specifically, Wechsler believed that organic brain disease, psychoses, and emotional disorders gave rise to a marked V > P pattern, whereas adolescent psychopaths and persons with mild mental retardation yielded a strong P < V pattern.
General Features of the Wechsler Tests :
The latest editions of the Wechsler intelligence tests -the WPPSI-IV, WISC-IV, and WAIS-IV—possess the following common features:
• Thirteen to fifteen subtests. The multi subtest approach allows the examiner to analyze intra-individual strengths and weaknesses rather than just to compute a single global score. In addition, it is possible to combine subtest scores in theoretical meaningful ways that provide useful information on the broad factors of intelligence. As the reader will learn subsequently, the pattern of subtest and factor scores may convey useful information that is hidden in the overall level of
performance.
• An empirically based breakdown into composite scores and a full scale IQ. Whereas the original Wechsler intelligence scales provided only two composite scores—Verbal IQ and
Performance IQ—the revisions have been moving toward a more sophisticated partitioning into composites confirmed from
factor-analytic research. The WISC-IV and WAIS-IV now yield composite or index scores in the same four areas:
performance.
• An empirically based breakdown into composite scores and a full scale IQ. Whereas the original Wechsler intelligence scales provided only two composite scores—Verbal IQ and
Performance IQ—the revisions have been moving toward a more sophisticated partitioning into composites confirmed from
factor-analytic research. The WISC-IV and WAIS-IV now yield composite or index scores in the same four areas:
Verbal Comprehension
Perceptual Reasoning
Working Memory
Processing Speed
Perceptual Reasoning
Working Memory
Processing Speed
The WPPSI-IV provides five index scores similar to the above (for ages 4:0 to 7:7) but also includes a Fluid Reasoning composite.
• A common metric for IQ and Index scores.The mean for IQ and Index scores is 100 and the standard deviation is 15 for all tests and all age groups. In addition, the scaled scores on each subtest have a mean of 10 and a standard deviation of approximately 3, which permits the examiner to analyze the subtest scores of the examinee for relative strengths and weaknesses.
• Common subtests for the different test versions. For example, the preschool, child, and adult Wechsler tests (WPPSI-IV, WISC-IV, and WAIS-IV) all share a common core of the same six subtests . An examiner who masters the administration of a core subtest on any of the Wechsler tests (such as the Information subtest on the WAIS-IV) easily can transfer this skill within the Wechsler family of intellectual measures.
Subtest Composition of the Wechsler Intelligence Tests
General Types of Items Used in Wechsler Tests
Subtest: -----------------Description
INFORMATION --------In what continent is Brazil? Questions such as these, which are wide-ranging and tap general knowledge, learning, and memory, are asked. Interests, education, cultural background, and reading skills are some influencing factors in the score achieved.
COMPREHENSION.--------- In general, these questions tap social comprehension, the ability to organize and apply knowledge, and what is colloquially referred to as “common sense.” An illustrative question is Why should children be cautious in speaking to strangers?
SIMILARITIES. ------------ How are a pen and a pencil alike? This is the general type of question that appears in this subtest. Pairs of words are presented to the examinee, and the task is to determine how they are alike. The ability to analyze relationships and engage in logical, abstract thinking are two cognitive abilities tapped by this type of test.
ARITHMETIC.----------- Arithmetic problems are presented and solved verbally. At lower levels, the task may involve simple counting. Learning of arithmetic,alertness and concentration, and short-term auditory memory are some of the intellectual abilities tapped by this test.
VOCABULARY.------------The task is to define words. This test is thought to be a good measure of general intelligence, although education and cultural opportunity clearly contribute to success on it.
RECEPTIVE VOCABULARY -----The task is to select from four pictures what the examiner has said aloud. This tests taps auditory discrimination and processing,auditory memory, and the integration of visual perception and auditory input.
PICTURE NAMING --------The task is to name a picture displayed in a book of stimulus pictures. This test taps expressive language and word retrieval ability.
DIGIT SPAN------------The examiner verbally presents a series of numbers, and the examinee’s task is to repeat the numbers in the same sequence or backwards. This subtest taps auditory short-term memory, encoding, and attention.
LETTER-NUMBER SEQUENCING-------------Letters and numbers are orally presented in a mixed-up order. The task is to repeat the list with numbers in ascending order and letters in alphabetical order. Success on this subtest requires attention, sequencing ability, mental manipulation, and processing speed.
PICTURE COMPLETION -------The subject’s task here is to identify what important part is missing from a picture. For example, the testtaker might be shown a picture of a chair with one leg missing. This subtest draws on visual perception abilities, alertness, memory, concentration, attention to detail, and ability to differentiate essential from nonessential detail. Because respondents may point to the missing part, this test provides a good nonverbal estimate of intelligence. However, successful performance on a test such as this still tends to be highly influenced by cultural factors.
PICTURE ARRANGEMENT ---------In the genre of a comic-strip panel, this subtest requires the testtaker to re-sort a scrambled set of cards with pictures on them into a story that makes sense. Because the test taker must understand the whole story before a successful re-sorting will occur, this subtest is thought to tap the ability to comprehend or “size up” a situation. Additionally, attention, concentration, and ability to see temporal and cause-and-effect relationships are tapped.
BLOCK DESIGN.----------A design with colored blocks is illustrated either with blocks themselves or with a picture of the finished design, and the examinee's task is to reproduce the design. This test draws on perceptual-motor skills, psychomotor speed, and the ability to analyze and synthesize. Factors that may influence performance on this test include the examinee’s color vision, frustration tolerance, and flexibility or rigidity in problem solving.
OBJECT ASSEMBLY --------- The task here is to assemble, as quickly as possible, a cut-up picture of a familiar object. Some of the abilities called on here include pattern recognition, assembly skills, and psychomotor speed. Useful qualitative information pertinent to the examinee’s work habits
may also be obtained here by careful observation of the approach to the task. For example, does the examinee give up easily or persist in the face of difficulty?
may also be obtained here by careful observation of the approach to the task. For example, does the examinee give up easily or persist in the face of difficulty?
CODING --------------- If you were given the dot-and-dash equivalents of several letters in Morse code and then had to write out letters in Morse code as quickly as you could, you would be completing a coding task. The Wechsler coding task involves using a code from a printed key.The test is thought to draw on factors such as attention, learning ability, psychomotor speed, and concentration ability.
SYMBOL SEARCH----------The task is to visually scan two groups of symbols, one search group and one target group, and determine whether the target symbol appears in the search group. The test is presumed to tap cognitive processing speed.
MATRIX REASONING--------- A non verbal analogy-like task involving an incomplete matrix designed to tap perceptual organizing abilities and reasoning.
WORD REASONING.--------- The task is to identify the common concept being described with a series of clues. This test taps verbal abstraction ability and the ability to generate alternative concepts.
PICTURE CONCEPTS-------- The task is to select one picture from two or three rows of pictures to form a group with a common characteristic. It is designed to tap the ability to abstract as well as categorical reasoning ability.
CANCELLATION----------- The task is to scan either a structured or an unstructured arrangement of visual stimuli and mark targeted images within a specified time limit. This subtest taps visual selective attention and related abilities.
No comments:
Post a Comment