Handbook of psychology volume 7 educational psychology
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- Subtypes 471
- A Simple Model of Subtypes
- Spelling: A Digression
- Reading Disabilities
- Types of Learning Disabilities 473
- Arithmetic Disabilities
470 Learning Disabilities naming, and morphophonemic knowledge). The language skills closest to normal involved the higher levels of seman- tic knowledge. The language test profiles of the three types were not as sharply differentiated as were their reading test profiles.
A battery of 37 neuropsychological tests was administered to determine the extent to which neuropsychological deficits interacted with each type of reading disability and to estimate the types of brain dysfunctions potentially associated with the reading disabilities. Factor analysis of the results did not differentiate any characteristic profiles of neuropsychologi- cal deficit. In addition, there was very little indication of any difference in relative incidence, localization, or severity of cerebral dysfunction among the three types of reading disabilities. This study suffers from many of the same definitional problems as most other subtype studies do. A lag of approxi- mately 2 years on reading measures defines the reading dis- ability, and the study did not account for the fact that 2 years below grade level means very different things for a child in Grade 3 as opposed to a child in Grade 8. In this study, the age of the subjects sampled was extremely diverse (8–27 years), which means that there were enormous variations in the severity of the reading disability. It is hardly surprising that qualitative and quantitative differences in the reading perfor- mances of such a would emerge, but whether it makes sense to speak of subtypes rather than a range of performance de- pending on severity of deficits is questionable. The fact that normal readers scored below average in many related mea- sures and individuals with reading problems scored in the normal range for some skills further confuses the interpreta- tion. There seems to be a problem with the sensitivity of some of the measures used or alternatively with their relevance to a reading deficit. The volume of results at which one arrives after all these tests are administered is formidable but at the same time very confusing. It would probably make far more sense to break down the reading process itself into crucial areas and see how the participants performed in each area— for example, oral reading in context, word recognition, word attack, and silent reading. The findings from a more focused and detailed analysis of fewer measures might be more mean- ingful. The fact that 30–60% of the participants fell within the normal range on the oral reading tests makes one really wonder about the definition of reading disability in this study. Furthermore, because a number of participants were clas- sified into more than one type and had profiles characteristic of combined types, separation into three distinct groups be- comes even more questionable. It seems that if one tested enough individuals (including normally functioning individ- uals) on enough measures, one would find enormous ranges of performances in both quality and quantity; it is question- able, however, how worthwhile it is to define them as differ- ent subtypes of a reading disability. The authors suggest that there seems to be a form of continuity between types, and I think that that is exactly what this study is all about. Most probably the authors have taken an extremely heterogeneous group of children in terms of reading performance and have emerged with three groups who are at different stages of the reading performance continuum. These styles of performing cannot be considered subtypes; rather, they represent differ- ent degrees of severity of a problem. As with the language tests, the neuropsychological tests only reflected the heterogeneity of the group or in fact perhaps any reading-disabled group. With a more narrowed selection of measures and a detailed error analysis of actual reading per- formance (rather than a list of scores on so many measures), more meaningful subtypes might emerge. This study illus- trates how inherent heterogeneity of the population under dis- cussion affects subtypes. Doehring et al. found a significant overlap between reading-disabled and normal individuals on a variety of measures that tested the child’s understanding of basic syntax using similar but not identical measures. There was also a great deal of variability within each of the subtypes that they identified. Siegel and Ryan (1984) have found virtually no overlap between reading-disabled and nor- mally achieving children but found that the performance of the reading-disabled children was very significantly below that of normally achieving children of the same chronological age. Siegel and Ryan’s subjects were homogeneous and se- lected on the basis of low scores on a word-reading test. Rutter, Yule, and associates proposed the existence of two subtypes of reading disorders. They used a regression equa- tion in which the expected reading level was predicted from a child’s IQ score (e.g., Rutter, 1978; Rutter, Tizard, & Whitmore, 1970; Rutter & Yule, 1973; Yule, 1967; Yule, Rutter, Berger, & Thompson, 1974). According to these au- thors, if the child’s reading level is significantly lower than that predicted from his or her IQ, then the child is said to be a
(children who are at the bottom end of the reading attainment continuum) and retarded readers (children who are under- achieving in relation to their chronological age and general level of intelligence) in sex distribution, neurological corre- lates, and association with speech and language disorders. It should be noted that there was considerable overlap be- tween the groups. Retarded readers who had (by definition) higher IQs were worse in their accuracy but not in compre- hension and were worse in spelling but had higher scores in mathematics. We do not believe that these constitute meaningful subgroups. It is important to note that language Subtypes 471 measures (WISC) constituted part of the definition of IQ. Children with learning disabilities have language problems (Siegel, 1985a, 1985b; Siegel & Ryan, 1984; Vellutino, 1977, 1978, 1979); therefore, children will have lower IQ scores when a language-based test is used as a measure of IQ. It is impossible to measure IQ independently of language and reading skills. A definition in which subtypes are developed on the basis of IQ-reading level discrepancies therefore seems to be invalid (see previous discussion). The distinction between reading retardation and reading backwardness may represent a difference of severity in that children who are backward in reading have more cognitive deficits than do those who are retarded in reading (and hence have lower IQ scores). Although Doehring (1984) notes that most subtype classi- fications of reading problems involve a visual nonverbal sub- type, I contend that the appearance of this subtype is an artifact of the tests of reading used. When a subtype such as this one with visual nonverbal problems is used, I contend that they also have language problems, that they are the chil- dren with good phonics skills but low comprehension scores, or that their word recognition skills are adequate but because of attention difficulties they have problems with memory, speed, attention, strategies in relation to reading, or any com- bination of these problems. Therefore, conclusive and convincing evidence of sub- types of reading disability has not emerged. In addition, there is homogeneity within the reading-disabled population. Ap- parent heterogeneity is a function of the definition used. As Doehring suggests, “The one simplifying assumption that I will continue to make for the present in my own work how- ever is that the most profound reading disabilities involve difficulty in acquiring lower level coding and word recogni- tion skills rather than higher-level skills and strategies” (Doehring, 1984, p. 211). If investigators use a word- recognition definition, phonics (nonword) definition, or both of reading disability, there will not be a significant amount of variability on relevant cognitive functions within the reading- disabled population. Reading disability involves a problem with phonological processing, language, and memory for verbal information. Reading-disabled children can be differentiated from other LD children on these variables. Visuospatial and perceptual- motor problems may also occur in dyslexia, but they are not the basic problem, nor are they characteristic of all dyslexic individuals in the same way in which language problems are.
If a logically consistent definition of dyslexia is used, all dyslexic (reading disabled) children have problems with language.
What emerges from this confusing array of studies is the fact that there are clearly two subtypes of learning disability— namely, a reading disability (dyslexia) and an arithmetic dis- ability. These subtypes have been validated in child and adult populations (e.g. Rourke & Strang, 1978; Shafrir & Siegel, 1994b; Siegel & Ryan, 1988, 1989a, 1989b). Shafrir and Siegel (1994b) compared three groups—individuals with arithmetic disability (AD), reading disability (RD), and both reading and arithmetic disabilities (RAD), with a comparison group with normal achievement (NA)—on a variety of cog- nitive and achievement measures. The main findings were as follows: (a) Each of the groups differed significantly from the others on tests of reading, spelling, memory, and other cogni- tive measures; (b) both the RD and RAD groups showed a deficit in phonological processing, vocabulary, spelling, and short-term memory; (c) the AD group performed similarly to the NA group on pseudoword reading and phonological pro- cessing but performed more poorly than did the NA group on word reading and vocabulary; (d) on many tasks, the RAD group performed more poorly than did the other groups; and (e) the AD and RAD groups performed more poorly than did the NA and RD groups on a visuospatial task. Therefore, this classification scheme for the subtyping of learning disabili- ties in adults appears to have validity.
Problems with spelling do exist, but they can co-occur with either reading or arithmetic difficulties, and it is rare to find a child who has difficulties with spelling and no problems in any other areas of functioning. Some children may have spe- cific difficulties with spelling when they are required to write the word from memory rather than when they are required to recognize the correct spelling of a word. In addition, English words are characterized by both regu- lar spelling (e.g., singing, print)—that is, words in which the letter-sound correspondences are predictable—and irregular spelling—that is, spelling that is not predicted from the rules of spelling-sound correspondence (e.g., island, knight). The possibility exists that children may be able to spell regular words but have more difficulty with the irregular words. In any case, spelling difficulties do occur but (as noted earlier) usually in combination with other problems. Furthermore, studies such as Jorm (1981), and Lennox and Siegel (1993, 1996) have found significant differences in the understanding of letter-sound correspondence rules and the orthographic awareness between children who were poor readers and spellers and children who were only poor spellers. On the 472 Learning Disabilities basis of findings such as these and for the reasons discussed previously, reading and spelling need to be treated as separate variables. TYPES OF LEARNING DISABILITIES Over the past 30 years, it has become clear that there are two major clusters of learning difficulties. The most commonly known is a reading disability, sometimes called dyslexia. There is no difference in meaning between the terms dyslexia and reading disability. Another equally prevalent but less commonly known disability is an arithmetic (mathematics) disability, sometimes called nonverbal learning disability, developmental output failure, writing-arithmetic disability, or visual-spatial disability. Although there is, admittedly, some heterogeneity within the two major clusters, they do share enough common characteristics to be considered as specific entities. Reading Disabilities Depending on the theoretical bias of the particular investiga- tor, the country, the circumstances, and so on, the word
there is no difference between dyslexia and a reading disabil- ity; they are exactly the same. Dyslexia involves difficulties with phonological process- ing, including such abilities as knowing the relationship be- tween letters and sounds and phonological awareness—that is, the ability to segment the speech stream into separate ele- ments. Over the years, a consensus has emerged that one core deficit in dyslexia is a severe difficulty with phonological processing (e.g., Rack, Snowling, & Olson, 1992; Siegel, 1993b; Snowling, 1980; Stanovich, 1988a, 1988b). Children with a reading disability have a core deficit in phonological processing. The evidence that is available clearly demon- strates that adults with dyslexia have deficits in phonological processing (e.g., Bruck, 1990, 1992; Elbro, Neilsen, & Petersen, 1994; Felton, Naylor, & Wood, 1990; Gottardo, Siegel, & Stanovich, 1997; Greenberg, Ehri, & Perin, 1997; Pennington, Van Orden, Smith, Green, & Haith, 1990; Pratt & Brady, 1988; Read & Ruyter, 1985; Russell, 1982; Scarborough, 1984; Shafrir & Siegel, 1994a, 1994b; Siegel, 1998). Most individuals with dyslexia show problems in the area of memory and language (Siegel & Ryan, 1984, 1988; Snowling, 1980; Stanovich, 1988a, 1988b; Vellutino, 1978). Usually individuals with dyslexia have spelling problems, but the presence of spelling difficulties without reading diffi- culties does not indicate dyslexia. A definition of dyslexia that captures the other problems that often co-occur with it is illustrated in Padget et al. (1996): Dyslexia is a language-based learning disorder that is biological in origin and primarily interferes with the acquisition of print lit- eracy (reading, writing, and spelling). Dyslexia is characterized by poor decoding and spelling abilities as well as deficit in phonological awareness and/or phonological manipulation. These primary characteristics may co-occur with spoken lan- guage difficulties and deficits in short-term memory. Secondary characteristics may include poor reading comprehension (due to the decoding and memory difficulties) and poor written expres- sion, as well as difficulty organizing information for study and retrieval. (p. 55) Current theories of the development of reading skills in English stress that phonological processing is the most significant underlying cognitive process (Stanovich, 1988a, 1988b, 1988c). Children and adults with a reading disability have difficulty with phonological processing. Phonological processing involves a variety of functions, but in the context of the development of reading skills, the most significant in the association of sounds with letters or combinations of letters. This function is referred to as the understanding of grapheme- phoneme conversion rules, and because of the irregular nature of the correspondences in English, the learning of these rules is a very complex process. The child who is learning to read must map oral language onto written language by decompos- ing the word into phonemes and associating each letter (or combination of letters) with these phonemes. The task of the beginning reader is to extract these grapheme-phoneme conversion rules. The alternative is sim- ply to memorize each word as a visual configuration and to associate a meaning with it. This kind of learning may occur, but it is inefficient and makes tremendous demands on visual memory. In English, no one-to-one correspondence exists between a letter (or letters) and a sound. The same letter rep- resents different sounds, and the same sound may be repre- sented by different letters. In an alphabetic language such as English, the best mea- sure of phonological processing skills is the reading of pseudowords—that is, pronounceable combinations of letters that can be read by the application of grapheme-phoneme con- version rules but that are, of course, not real words in English. Examples, include such pseudowords as shum, laip, and
with the grapheme-phoneme conversion rules of English even though they are not real words and have not been encountered in print or in spoken language before. The development of the ability to read pseudowords has been studied extensively (e.g., Calfee, Lindamood, & Types of Learning Disabilities 473 Lindamood, 1973; Hogaboam & Perfetti, 1978; Siegel & Ryan, 1988; Venezky & Johnson, 1973). Ample evidence in- dicates that children with dyslexia have a great deal of diffi- culty reading pseudowords. Studies such as those of Bruck (1988), Ehri and Wilce (1983), Snowling (1980), Siegel and Ryan (1988), and Waters, Bruck, and Seidenberg (1985) have shown that disabled readers have more difficulty reading pseudowords than do normal readers matched on either chronological age or reading level. For example, Siegel and Ryan (1988) studied the development of the ability to read pseudowords in normal and disabled readers aged 7–14 years. By the age of 9, the normal readers were quite profi- cient and performed at almost a perfect level for even the most difficult pseudowords, with—in some cases—as many as three syllables. Similarly, Backman, Bruck, Hebert, and Seidenberg (1984) showed that 10-year-olds perform as well as do adults on tasks involving the reading of pseudowords; however, Siegel and Ryan (1988) found that the performance of the reading-disabled children was quite different. These children appear to acquire these reading skills very late in de- velopment, and even reading-disabled children at the age of 14 were performing no better than were normal readers at the age of 7. To control (at least partially) for experience with print, Siegel and Ryan (1988) used a comparison of disabled and normal readers matched on reading grade level. Even when the disabled readers and the normal readers were matched on reading level (hence, the disabled readers were considerably older than the normal readers), the performance of the reading-disabled individuals on a task involving the reading of pseudowords was significantly poorer than that of the normal readers. Thus, difficulties with phonological processing seem to be the fundamental problem of children with reading disability, and this problem continues to adulthood. Many adults with a reading disability become reasonably fluent readers but still have difficulty reading pseudowords or read them very slowly (e.g., Barwick & Siegel, 1996; Bruck, 1990). For children learning to read English, the learning of grapheme-phoneme conversion rules is a result of systematic instruction, and the extraction of the rules is a result of re- peated encounters with print. No evidence is available as to how much of the development of decoding skills is a result of specific instruction in the grapheme-phoneme conversion rules and how much is a result of experience with print. In any case, the understanding of the grapheme-phoneme con- version rules develops rapidly in the first years of experience with print under normal conditions. Some individuals have difficulties only with writing, spelling, or both. Because these written language problems usually occur in the context of problems with reading prob- lems, arithmetic and mathematics problems, or both, the exis- tence of a separate written language disability is not clearly established, nor is there a clear definition of it, especially in the adult population. Spelling difficulties can occur in the absence of severe reading disabilities (e.g., Bruck & Waters, 1988; Lennox & Siegel, 1993). There also may be problems with un- derstanding or producing language. These problems have not been documented as distinct learning disabilities and are often components of dyslexia. If learning disabilities are to be treated as measurable entities and if individuals are to receive educational services based on the presence of a single or mul- tiple learning disabilities, it is then obviously important to determine what these learning disabilities are.
Individuals with developmental output failure or writing- arithmetic disability have difficulty with computational arithmetic and written language, typically in the absence of reading difficulties, although this disability can co-occur with dyslexia. They often have difficulties with spelling and have problems with fine-motor coordination, visuospatial process- ing, and short-term and long-term memory (e.g., multiplica- tion tables), but they usually have good oral language skills (Fletcher, 1985; Johnson & Mykelbust, 1967; Kinsbourne & Warrington, 1963; Kosc, 1974; Levine, Oberklaid, & Meltzer, 1981; Morrison & Siegel, 1991a, 1991b; Rourke, 1991; Rourke & Finlayson, 1978; Shafrir & Siegel, 1994b; Siegel & Feldman, 1983; Siegel & Linder, 1984; Spellacy & Peter, 1978). Rourke and his associates (e.g., Rourke, Del Dotto, Rourke, & Casey, 1990; Rourke & Tsatsanis, 1996) have described a syndrome called nonverbal learning dis-
ever, the operational definition of this learning disability is problematic; it is not clear how a diagnosis can be made. Often, these individuals have verbal IQ scores significantly higher than performance IQ, but this discrepancy is neither necessary nor sufficient to make the diagnosis. Often, they have lower arithmetic scores than reading scores, but the dif- ferences between these scores are not always significant (e.g., Rourke et al., 1990). (For an extended discussion of the defi- nitional issue and conceptualization of this disability, see Morrison & Siegel, 1991a.) Investigators (e.g., Fletcher, 1985b; Rourke & Finlayson, 1978; Rourke & Strang, 1978; Siegel & Feldman, 1983; Siegel & Ryan, 1984, 1988, 1989a, 1989b) have found evi- dence that children with specific arithmetic deficits and aver- age or above-average word recognition scores on the WRAT appear to have a variety of cognitive and neuropsychological
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