Handbook of psychology volume 7 educational psychology
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- Subtyping Models
- Academic Performance Models
- Subtypes 465
- Subtypes Within the Reading Disability Group
462 Learning Disabilities with phonological processing, word recognition, or both is used as the basis of the definition of a reading problem, then disabled readers appear to have reasonably homogeneous cognitive profiles and—in particular—deficits in the language areas (e.g., Fletcher, 1985; Rourke & Finlayson, 1978; Rourke & Strang, 1978; Siegel & Ryan, 1984, 1988, 1989b; Strang & Rourke, 1983b). Therefore we and others (e.g., Siegel & Heaven, 1986; Siegel & Ryan, 1989a; Vellutino, 1978, 1979) argue that single-word or nonword reading con- stitute the purest measures of reading and that an operational definition of a reading disability should be based on nonword tests to measure phonological skills, single-word tests to measure word recognition skills, or both. The classification of children with arithmetic problems is equally problematic. As Siegel and Ryan (1989a) note, it is almost impossible to find a group of reading-disabled children who also do not have severe deficits in arithmetic. At the same time, a number of investigators (Fletcher, 1985b; Rourke & Finlayson, 1978; Rourke & Strang, 1978; Siegel & Feldman, 1983; Siegel & Linder, 1984; Siegel & Ryan, 1984, 1988, 1989a) have found a group of learning-disabled children with difficulties in arithmetic but with average or above-average reading scores. Some evidence (e.g., Fletcher, 1985a; Rourke & Finlayson, 1978; Rourke & Strang, 1978; Siegel & Feldman, 1983; Siegel & Linder, 1984; Siegel & Ryan, 1984, 1988, 1989a) suggests that these children with arithmetic deficits but normal reading (word recognition) have cognitive profiles that are different from those of chil- dren with reading difficulties. Therefore, it is important that children designated as arithmetic LD not have problems that are confounded by difficulties in reading. SUBTYPES Given the heterogeneity of LD groups, Siegel (1988b) con- tends that if all LD children are grouped together, then inac- curate conclusions may be reached. Evidence in support of this position has been found by many investigators (e.g., Fletcher, 1985; McKinney, Short, & Feagans, 1985; Rourke & Finlayson, 1978; Siegel & Linder, 1984; Siegel & Ryan, 1984, 1988, 1989a, 1989b). For example, Siegel and Ryan (1984, 1988, 1989a, 1989b) and Fletcher (1985) found differences between specific arithmetic-disabled children without reading problems and reading-disabled children in both short-term and working memory. McKinney et al., using a cognitive battery designed to assess a wide range of linguis- tic and perceptual abilities, were able to classify 55 first- and second-grade, school-identified LD children into six subtypes. They then demonstrated that the three subtypes with atypical cognitive profiles had poorer academic outcomes than did the three groups with normal or near-normal profiles. These differences might not have been evident had these chil- dren been grouped together and not divided into subtypes. Because of this heterogeneity of LD groups, considerable effort has been made to identify specific subgroups of LD children who share common attributes that distinguish them from other subtypes. Not only do subtypes exist, but they also seem to take several forms in terms of achievement patterns, associated cognitive information-processing abilities, or both. Furthermore, these subtypes may vary as a function of etiology and age (e.g., McKinney et al., 1985; Rourke & Finlayson, 1978; Satz & Morris, 1981; Short, Feagans, McKinney, & Appelbaum, 1986; Siegel & Heaven, 1986). Subtyping Models Early subtype approaches are based on clinical inferences that have attempted to reduce complex data sets of subjects into presumably homogeneous classes largely based upon a priori considerations and visual inspection techniques. These methods have been criticized for their inability to manage simultaneously large quantities of information in an objec- tive fashion as well as for the subjectivity that results from the bias of clinical decisions made at various stages during the sub- type development and subject classification (see Satz & Morris, 1981, and Hooper & Willis, 1989, for a complete review). More recently, with the availability of advanced computer technology, empirical classification models using applied descriptive multivariate statistics have been developed. This approach has involved a search for hidden structure in com- plex multidimensional data sets generally involving cogni- tive linguistic skills or direct measures of achievement or behavior (e.g., Doehring & Hoshko, 1977; Feagans & Appelbaum, 1986). These methods also have difficulties. Hooper and Willis (1989) contend that standards of reliability and validity have frequently been overlooked or marginally addressed by inves- tigators using these classification techniques. In addition, they suggest that “the adequacy and strength of models derived by empirical classification methods are influenced by many a pri- ori clinical decisions including those regarding theoretical orientation, sample selection, and variable selection” (p. 104). Thus, the appropriate subtyping model remains an open ques- tion and may depend on the type of research undertaken.
In spite of the difficulties inherent in subtyping models, a num- ber of investigators (e.g., Fletcher, 1985; Rourke & Finlayson,
Subtypes 463 1978; Rourke & Strang, 1978; Siegel & Feldman, 1983; Siegel & Linder, 1984; Siegel & Ryan, 1984, 1988, 1989a, 1989b) have suggested that LD students in general can be di- vided on the basis of their academic achievement as measured by Wide Range Achievement Test (WRAT) scores in reading, spelling, and arithmetic. Although each investigator has cre- ated his or her own classification scheme, two broad cate- gories of subtype groups have emerged. The first contains children with at least reading deficits, and the second contains children with at least arithmetic deficits and normal-to-above- normal reading scores. Some authors (e.g., Fletcher, 1985; Rourke & Finlayson, 1978; Rourke & Strang, 1978) have sub- divided these groups further, basing their divisions on the presence of other deficits. For example, Siegel and Linder (1984) and Siegel and Ryan (1984, 1988, 1989a, 1989b) have used only two academic subtypes: (a) an arithmetic-disabled group, defined by scores equal to or below the 25th percentile on the WRAT Arithmetic subtest and scores equal to or above the 30th percentile on the WRAT Reading subtest and (b) a reading-disabled group, defined by scores equal to or below the 25th percentile on the WRAT Reading subtest and no cutoffs for the other two WRAT subtests. Fletcher (1985b) has developed the following four subtypes: (a) a reading-spelling- disabled group, (b) a reading-spelling-arithmetic-disabled group, (c) an arithmetic-disabled group, and (d) a spelling- arithmetic-disabled group. According to this categorization, the reading-spelling-disabled group is defined as consisting of children with (a) WRAT Reading and Spelling subtest scores below the 31st percentile, (b) WRATArithmetic subtest scores above the 30th percentile, and (c) the arithmetic score must be at least one-half standard deviation above the reading score on the appropriate WRAT subtest. The reading-spelling-arith- metic-disabled group is characterized by children with scores on all three WRAT subtests below the 31st percentile. The arithmetic-spelling-disabled group contains children who have (a) WRAT Spelling and Arithmetic subtest scores below the 31st percentile, (b) WRAT Reading subtest scores above the 39th percentile, and (c) at least one standard deviation between their reading and arithmetic scores. The arithmetic- disabled group consists of children who have (a) WRAT Reading and Spelling subtest scores above the 39th percentile, (b) WRATArithmetic subtest scores below the 31st percentile, and (c) difference of at least one standard deviation between their reading and arithmetic scores. In contrast, a series of studies by Rourke and his associates (Rourke & Finlayson, 1978; Rourke & Strang, 1978; Strang & Rourke, 1983a, 1983b) have identified the following three subtypes: (a) a gen- eral disabled group (reading-spelling-arithmetic-disabled), (b) a reading-disabled group, and (c) an arithmetic-disabled group. These investigators defined their reading-spelling- arithmetic groups as consisting of children with WRAT subtest scores below the 19th percentile on all three subtests. The reading-spelling-disabled group consisted of children with (a) WRAT Arithmetic subtest scores at least 1.8 years higher than their WRAT Reading and Spelling subtest scores and (b) WRAT Reading and Spelling subtest scores below the 15th percentile. The arithmetic-disabled group contained children whose WRAT Reading and Spelling subtest scores were at least 2 years above the WRAT Arithmetic subtest scores. Rourke and colleagues have developed subtypes of LD children based on patterns of academic performance (Fisk & Rourke, 1979, 1983; Ozols & Rourke, 1985; Porter & Rourke, 1985; Petrauskas & Rourke, 1979; Rourke & Finlayson, 1978; Rourke & Strang, 1978; Rourke & Fisk, 1981; Strang & Rourke, 1983, 1985a, 1985b; Sweeney & Rourke, 1978). Depending on the particular investigation, percentile cutoff scores of 20, 25, or 30 on the WRAT have been used to define a particular LD group. In one study, Rourke and Finlayson (1978) investigated the performance of three groups of LD children on a neu- ropsychological battery. The subtypes were formed on the basis of their WRAT scores in reading, spelling, and arith- metic. The first subtype exhibited uniformly deficient perfor- mance in all three academic areas. They were found to be superior to a specifically arithmetic-disabled group on measures of visual-perceptual and visuospatial abilities. In the second subtype, children were relatively good at arith- metic as compared to their reading and spelling, but all areas were below average. Superior visuospatial abilities and Per- formance IQ scores were characteristic of this subtype. The third subtype was composed of children whose reading and spelling scores were average or above, but whose arithmetic score was at least 2 years below that. This group exhibited Verbal IQ scores that were higher than their Performance scores. Their performance on measures of visual-perceptual- organizational skills was somewhat deficient. Their per- formance on measures of verbal and auditory-perceptual abilities was superior to that of the first two groups, who were reading disabled and low achievers in arithmetic. Rourke and Strang (1978) found further deficiencies in this third subtype on complex psychomotor measures and differences in hand superiority on the Tactual Performance Test. Difficulties in visuospatial orientation, including right-left problems, and impaired bilateral tactile-perceptual abilities, including finger agnosia, were also characteristic of this group. Strang and Rourke (1983a, 1983b) found that the specific arithmetic-disabled children made significantly more errors than did the reading and arithmetic disabled children on the Halstead category test. The arithmetic-disabled children had
464 Learning Disabilities lower scores on those subtests, which “require a substantial degree of ‘higher order’ visual-spatial analysis” (Strang & Rourke, 1985b, p. 173). An analysis of the arithmetic errors made by the third group (specifically arithmetic disabled) on the WRAT subtest indicated a large number and variety of errors. The quality of errors, as expected, changed somewhat with age. The most prevalent types of mechanical errors were identified as follows: (a) spatial organization, (b) visual de- tail, (c) procedural errors, (d) failure to shift psychological set, (e) graphomotor, (f) memory, and (g) judgment and rea- soning, indicating deficits in visuospatial and perceptual- motor abilities. Ozols and Rourke (1985) compared the performance of two groups of LD children to a group of average-achieving children of the same age on four tasks—two verbal and two nonverbal. The groups were identified as follows: (a) a language-disorder group, who exhibited relatively well- developed visuospatial abilities but poor auditory-perceptual and language-related abilities (WRAT subtest percentile scores in reading, spelling, and arithmetic were all below 25); (b) a spatial-disorder group, who exhibited relatively well- developed auditory-perceptual and language-related abilities but poor visuospatial abilities (WRAT arithmetic subtest score was the only percentile score below 25). The language- disorder group performed significantly more poorly on the verbal tasks than did the controls, and the spatial-disorder group performed significantly more poorly than did the con- trols on the nonverbal tasks. Siegel and Ryan (1984) used performance on achievement tests to subdivide LD children into more heterogeneous groups. Three LD groups were created and compared to a control group of normally achieving children. The LD groups were (a) reading-disabled children who had low scores on the WRAT Reading test, a test of word recognition skills; (b) children who were arithmetic written work disabled who had low scores on the WRAT Arithmetic test, a measure of computational arithmetic skills; and (c) children with atten- tion deficit disorder (ADD; hyperactive) but with no other learning disabilities. Typically, the reading-disabled children had significantly below-average ability to understand the syntactic and morphological aspects of language and—at the youngest ages—memory for sentences. None of the other LD groups showed deficits in these areas. The reading-disabled children had a significant deficit in reading and spelling non- words and in recognizing the visual form of a spoken sound. None of the other LD children had deficits in these areas, with the exception of the youngest, specifically arithmetic- disabled children, who had some difficulties with these phonological skills in spite of their normal word-recognition skills. This finding may be a result of the definition of arithmetic disability, which at the youngest ages involves memory skills in addition to computational skills. Thus, these younger arithmetic-disabled children may represent the more severely disabled children compared to older children who have a specific arithmetic disability. The children with ADD and no other difficulties with achievement did have signifi- cantly lower scores on a reading comprehension test (which is in reality a memory test and may require attentional skills), but these children showed no other deficits. All of the reading-disabled children had a severe deficit involving phonological skills. They were quite homogeneous in this respect. In most cases there was no overlap in the scores of the reading-disabled and normally achieving chil- dren of the same chronological age. Furthermore, for the reading and spelling of nonwords, the reading-disabled chil- dren performed more poorly than did younger controls matched for reading level, indicating a very serious deficit. The children with an arithmetic writing disability and the children with a reading disability had significantly lower scores on a short-term memory task involving visually pre- sented letters, but Siegel and Linder (1984) found that for auditorily presented letters, the arithmetic-disability group performed in the normal range, indicating that the deficit of this latter group was limited to short-term memory for visu- ally presented information. Fletcher (1985) used a verbal and nonverbal memory task to test the hypothesis that subgroups of disabled learners show different performance patterns. All tasks were based on selective reminding procedures (i.e., in subsequent presenta- tions, items are repeated only if they were not recalled on the previous trial) to determine what inferences could be drawn concerning storage and retrieval skills in these subgroups. Control subjects had to obtain percentile scores above 39 on the Reading, Spelling, and Arithmetic subtests of the WRAT and show no history of achievement difficulties. Disabled learners were placed into one of four groups depending on their pattern of WRAT scores. The groups were (a) reading- spelling-disabled (R-S), (b) reading-spelling-arithmetic- disabled (R-S-A), (c) spelling-arithmetic-disabled (S-A), and (d) arithmetic disabled (A). The findings indicated that not all LD children showed similar patterns of memory deficiencies. Children with read- ing problems showed only retrieval difficulties on verbal tasks, whereas children with arithmetic problems demon- strated both storage and retrieval problems on nonverbal tasks. Children with the R-S pattern had poorer verbal skills, whereas children with the arithmetic pattern showed poorer nonverbal skills. The R-S-A pattern had not been previously studied, but children demonstrating this pattern had relatively poor performance on the tasks used in this study.
Subtypes 465 Some studies were carried out in an attempt to determine the relative diagnostic power of a number of tests in dis- criminating between dyslexic children and those with other learning disabilities. In one study by Rudel and Denckla (1976), the performance of developmental dyslexic individu- als was tested using visual-verbal tasks, such as naming pic- tured objects, letters, and numbers. A 2-year or greater lag in reading performance on a test of oral reading skill led to a clas- sification of dyslexic. All participants were tested on rapid au- tomatized naming tasks. Stimuli included colors, numerals, use objects (e.g., comb), and high-frequency lowercase letters. The naming speed on all four tasks for normally functioning individuals was faster than for nondyslexic LD participants, and nondyslexic participants were significantly faster than dyslexic subjects. In this study, the experimental children were termed learn-
designated. The authors stated that division of participants into dyslexic and nondyslexic groups was done post hoc by determining the difference between reading age and mental age. Reading grade level was based on a test of oral reading skill; no mention was made of what oral reading test was used. The problems associated with such tests have already been discussed. The lack of information on the measures used in this study raises questions about the heterogeneity and sever- ity of the problems demonstrated by the group being studied. In a second study (Denckla, Rudel, & Broman, 1981), a series of tasks was administered: a rapid automatized naming task, the Oldfield-Wingfield Pictured Object Naming Test, visual-Braille letter learning (a paired associate learning task), visual-temporal spatial matching (a same or different response was required of the participant after he or she watched a series of light flashes emitted from a single sta- tionary point source in a black box), and finally the silent detection of repeated target symbols (a pencil-and-paper version of the visual matching task paradigm). The dyslexic group had a high percentage of dysphasic errors and pro- longed times on repeated naming compared to the non- dyslexic LD children. In this study, the participants were defined as dyslexic on the basis of a discrepancy between the WISC-R score and the score on the Gray Oral Reading Test. The same problems as in the earlier study emerge. The latter test is an oral reading comprehension test that cannot be regarded as a pure test of reading skill. Failure to do well on this test could be the result of poor decoding skills, poor attention, poor memory, or poor comprehension. The result is a heterogeneous sample with findings that have limited external validity. Another attempt at subtyping on the basis of achievement test scores is described by Satz and Morris (1981). Although their subtyping scheme resembles Rourke’s, it is flawed by the use of grade-level retardation on the WRAT subtests for classification. This scheme is particularly problematic with the many older children in the study. Rather than finding significant heterogeneity on language and memory functioning, these studies found homogeneity within the population of disabled readers. It is important to note that the studies that have found homogeneity within the reading-disabled population have used retardation in word- recognition skills to define the reading-disabled population. In one very early study on subtyping that was unsuccessful, it was found that all reading-disabled children had difficulty with sound blending and short-term memory (Naidoo, 1972). As discussed later in this chapter, studies that have used other definitions (reading comprehension) do not find the same de- gree of homogeneity. As further evidence of this point, Siegel and Ryan (1989b) found that when a definition of reading disability was used that involved poor word-recognition or phonics skills, reading-disabled children had significant problems with phonological processing and understanding of syntax. However, children with low reading comprehension scores but good phonics, word recognition skills, or both did not show these problems. In summary, with achievement test definitions such as those used by Rourke and associates, Fletcher, and Siegel and colleagues, fairly homogeneous groups of reading-disabled children have emerged. Regardless of the exact criteria used, this method of sub- typing had identified groups of LD children whose arithmetic difficulties are not confounded by deficits in reading (word recognition). The emergence of a specific arithmetic-disabled subgroup has permitted investigators to clarify some of the characteristics that distinguish this group from other LD children with reading deficits.
A number of investigators have assumed that a reading dis- ability is not a single disorder but rather represents a group of more specific subtypes. Some of these conceptualizations are outlined in the following discussion. However, what appears to be heterogeneity is really not; because of definitional inad- equacies, heterogeneity emerges. Several schemes have been used as subtyping systems. These schemes involve (a) the use of achievement tests to classify all LD children with the implicit assumption that all the children with a reading disability will show a reasonable similarity in cognitive performance and be different from those without a reading disability (as was described earlier), (b) the use of patterns of responses on reading tests to classify subgroups of dis- abled readers, (c) the use of neuropsychological measures to
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