Cerebellar Tests Differentiate between Groups of Poor Readers with and without IQ Discrepancy.
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| Title: | Cerebellar Tests Differentiate between Groups of Poor Readers with and without IQ Discrepancy. |
|---|---|
| Language: | English |
| Authors: | Fawcett, Angela J., Nicolson, Roderick I., Maclagan, Fiona |
| Source: | Journal of Learning Disabilities. Mar-Apr 2001 34(2):119-135. |
| Peer Reviewed: | Y |
| Page Count: | 17 |
| Publication Date: | 2001 |
| Document Type: | Journal Articles Reports - Research |
| Descriptors: | Dyslexia, Elementary Secondary Education, Intelligence Quotient, Learning Disabilities, Slow Learners |
| ISSN: | 0022-2194 |
| Abstract: | Tests of phonological, speed, motor and cerebellar tasks were given to 36 students with learning disabilities, 29 of whom were classified as non-discrepant (IQ<90) and 7 as discrepant, (IQ at least 90 and dyslexic). On the cerebellar tests of postural stability and muscle tone, the non-discrepant group performed significantly better than the children with dyslexia. (Contains references.) (Author/DB) |
| Entry Date: | 2001 |
| Accession Number: | EJ623212 |
| Database: | ERIC |
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| FullText | Links: – Type: pdflink Url: https://content.ebscohost.com/cds/retrieve?content=AQICAHj0k_4E0hTGH8RJwT4gCJyBsGNe_WN95AvKlDbXJGqwxwGHT7qx8dmAkYBiXO5Dk7pXAAAA4jCB3wYJKoZIhvcNAQcGoIHRMIHOAgEAMIHIBgkqhkiG9w0BBwEwHgYJYIZIAWUDBAEuMBEEDAbv-T16RoWhhCruFgIBEICBmk7wtsg5Qxhl6_0relpJ_13-9AuBHrNs1qlzMgDlw6EnUvT5_sYFtcSG0VfolR2eVfVjxNTAZa9nuaFhPPj24aRkJh9W1J-kZ2hOv5aldC-ZH01vksAoUJRy8_NW9OGT-sirTI49gnka15-XFA0AnWB_r4sDe8o-8_K281HhrdRt4icDqTsU8-4_89akYY_rPxz0RxPC147TfW0= Text: Availability: 1 Value: <anid>AN0004192409;LED01MAR.01;2001Mar20.21:37;v5.0</anid> <title id="AN0004192409-1">CEREBELLAR TESTS DIFFERENTIATE BETWEEN GROUPS OF POOR READERS WITH AND WITHOUT IQ DISCREPANCY </title> <hd id="AN0004192409-2"> Abstract </hd> <p>A comprehensive test battery, including phonological, speed, motor and cerebellar tasks, was administered to the entire cohort of two schools for children with learning disabilities. Testing was undertaken blind without accessing the psychometric data on the children. Children were then allocated to a discrepancy group on the basis of their IQ, with the majority (n = 29) classified as nondiscrepant (IQ less than 90) and a smaller set (n = 7), with IQ of at least 90, classified as discrepant (with dyslexia). Both groups showed significant deficits relative to age-matched controls on almost all the tests. On phonological, speed, and motor tasks, the nondiscrepant group were at least as severely impaired as the discrepant group. By contrast, on the cerebellar tests of postural stability and muscle tone, the nondiscrepant group performed significantly better than the children with dyslexia and close to the level of the controls. The findings indicate that cerebellar tests may prove a valuable method of differentiating between poor readers with and without IQ discrepancy. The findings are interpreted in terms of the cerebellar deficit hypothesis for dyslexia. </p> <p>Developmental dyslexia has been traditionally defined as "a disorder in children who, despite conventional classroom experience, fail to attain the language skills of reading, writing and spelling commensurate with their intellectual abilities" (World Federation of Neurology, 1968, p. 26). A recent redefinition "a specific language based disorder of constitutional origin, characterized by difficulties in single word decoding, usually reflecting insufficient phonological processing abilities" (Orton Society, 1995, pp. 16-17) reflects a major achievement of dyslexia research--the identification and analysis of a phonological deficit (Bradley &amp; Bryant, 1983; Shankweiler et al., 1995; Snowling, 1987; Stanovich, 1988a; Vellutino, 1979), which became the consensus view of many dyslexia researchers. The redefinition also reflects a more controversial change, however, in that, unlike the traditional definition, it does not mention discrepancy between reading performance and that expected on the basis of the child's intelligence. </p> <p>We review briefly the discrepancy-based research on reading performance that has led to the conclusion that poor readers are poor readers, regardless of IQ. This finding was a major factor in the aforementioned redefinition. We note, however, that it is quite possible that, although the reading-related symptoms of both groups of poor readers may be indistinguishable, the underlying causes may nonetheless differ To take everyday examples, many diseases or many automobile mechanical faults have similar symptoms despite different causes. We argue, therefore, that a powerful method of addressing the discrepancy issue is to investigate performance outside the reading domain. We have identified a set of such tasks that should discriminate between the extant hypotheses for the causes of dyslexia. This analysis led to the design used in this study. A range of tasks was administered to groups of nondiscrepant poor readers (NDPR), children with dyslexia, and control children matched for chronological age. Analysis of the profile of scores for the different groups allowed decisive tests to be undertaken. </p> <hd id="AN0004192409-3"> The Discrepancy Debate </hd> <p>An important early criticism of the use of IQ in defining dyslexia was presented by Siegel (1988). Siegel made a number of important criticisms, but the crux of her argument was stated succinctly in a subsequent commentary, "IQ scores do not predict different cognitive abilities within the population with reading disabilities. Poor readers of all IQ levels show equivalent difficulties with reading, spelling, phonological processing, short-term memory, and syntax" (Siegel, 1989, p. 518). Siegel (1992) presented a metastudy that further supported these conclusions. Additional problems for the use of IQ derived from analyses of the Connecticut Longitudinal Study (S. E. Shaywitz, Escobar, Shaywitz, Fletcher, &amp; Makuch, 1992), which concluded that "reading difficulties, including dyslexia, occur as part of a continuum that also includes normal reading ability. Dyslexia is not an all-or-none phenomenon, but like hypertension, occurs in degrees" (p. 145). </p> <p>Stanovich provided further incisive analyses (Stanovich, 1988a, 1988b; Stanovich &amp; Siegel, 1994), framing the following question: Do "garden-variety poor readers" (NDPR in our terminology) show phonological difficulties commensurate with those of children with dyslexia? Stanovich's question has been answered pretty decisively: Yes, NDPR children do show equivalent phonological difficulties to those with dyslexia (Aaron, 1997; Ellis, McDougall, &amp; Monk, 1996; Siegel, 1989, 1992). From this, following Siegel, Stanovich reasoned that poor phonological skills resulted in poor reading regardless of IQ and that, therefore, IQ was irrelevant to the definition of reading disability (Stanovich, 1991) and then, finally, that dyslexia may not exist as a separate syndrome (Stanovich, 1994). This led him to the conclusion that discrepant and nondiscrepant poor readers show a similar phonological core deficit, with variable differences outside the phonological area (Stanovich &amp; Siegel, 1994). This analysis has led some researchers in the field to argue that there is no longer any point in attempting to differentiate between children with dyslexia and children with more generalized learning difficulties, because they both show the same pattern of phonological difficulties. This view underlies the downplaying of discrepancy in the 1994 redefinition of dyslexia. For recent espousals of this view, see Gustafson and Samuelsson (1999), Siegel (1999), and Stanovich (1999). </p> <p>However, although this analysis of phonological skills and reading is sound, there remain strong grounds for retaining the discrepancy criterion. Nicolson (1996) argued that this analysis is appropriate only if the investigators' aim is simply to characterize the symptoms of poor reading in dyslexia or if the phonological deficit account is the only possible causal explanation for dyslexia. He made the point that it is important to distinguish between the causes and the symptoms of a disorder, citing the example of malaria and influenza, both of which have symptoms of high temperature, aching limbs and so forth, but have very different underlying causes and treatments. It is quite possible that, although phonological deficit symptoms occur for both types of poor readers, symptoms of the "true" underlying cause of dyslexia--symptoms that distinguish between poor readers with and without discrepancy--may arise outside the phonological domain and even outside the literacy domain. Indeed, since the early studies cited previously, three further possible causal explanations of dyslexia have been posited in addition to the phonological deficit hypothesis, all of which suggest that children with dyslexia will show not only phonological difficulties, but also difficulties outside the phonological domain, thereby allowing further critical tests to be undertaken. Specifically, the magnocellular deficit hypothesis, the double deficit hypothesis, and the cerebellar deficit hypothesis all suggest different explanations of why discrepancy is still crucial, even though phonological performance does not distinguish discrepant and nondiscrepant groups. We explain briefly each hypothesis, the evidence in its favor, and the means by which each hypothesis addresses the well-known phonological deficits of children with dyslexia. </p> <hd id="AN0004192409-4"> Causal Theories for Dyslexia </hd> <p> <bold> The Phonological Deficit Hypothesis. </bold> As noted, the Phonological Deficit hypothesis has been the dominant explanatory framework for dyslexia. It has argued that neurological abnormalities in the language areas around the Sylvian fissure lead to failure to develop phonological awareness skills at the age of 5, thereby interfering with the learning of phoneme-grapheme and grapheme-phoneme conversions, critical requirements in learning to read (Bradley &amp; Bryant, 1983; Wagner, 1988). There is evidence that phonological awareness deficits persist through life (Elbro, Nielsen, &amp; Petersen, 1994; Fawcett &amp; Nicolson, 1995a; Pennington, Vanorden, Smith, Green, &amp; Haith, 1990; Russell, 1982), that proactive training of at-risk children on phonological awareness leads to relatively typical acquisition of reading (Bradley, 1988; Lundberg, Frost, &amp; Petersen, 1988), that there is atypical brain activation when adults with dyslexia process. phonological stimuli (Fulbright et al., 1997; Georgiewa et al., 1999; Paulesu et al., 1996; Rumsey et al., 1997), and there is evidence of neuroanatomical abnormality in the peri-Sylvian regions (Clark &amp; Plante, 1998; Galaburda, Sherman, Rosen, Aboitiz, &amp; Geschwind, 1985; Jackson &amp; Plante, 1996; Pennington et al., 1999). No one would contest the significance of phonological impairment in dyslexia. Nonetheless, as Frith (1997) concludes, "the precise nature of the phonological deficit remains tantalisingly elusive" (p. 11). </p> <p> <bold> Magnocellular Deficit Hypotheses. </bold> There is extensive evidence of difficulties in sensory processing of almost all stimuli, at least for some children with dyslexia. Lovegrove (1993) established that children with dyslexia are less sensitive to visual flicker (see also Talcott et al., 1998). Tallal, Merzenich, Miller, and Jenkins (1993) have claimed that, like children with language disorders, children with dyslexia require longer to process rapidly changing auditory stimuli. Neuroanatomical abnormalities have been identified (Galaburda, Menard, &amp; Rosen, 1994; Livingstone, Rosen, Drislane, &amp; Galaburda, 1991) in both visual and auditory magnocellular pathways to the thalamus. Stein (e.g., Stein &amp; Walsh, 1997) suggested that visual magnocellular pathway abnormality may cause visual persistence, which would in turn lead to specific difficulties in reading. Both Stein and Tallal et al. have argued independently that there may be a pan-sensory magnocellular abnormality that leads to difficulties in most types of rapid processing. It is important to note, however, that magnocellular deficits are likely to lead to qualitatively different problems in visual and auditory modalities. In vision, deficits are predicted to occur for low-contrast or slowly moving stimuli (Eden et al., 1996; Stein &amp; Walsh, 1997), whereas in audition, deficits are predicted to occur for rapidly changing stimuli (Tallal et al., 1998; but see Mody, Studdert-Kennedy, &amp; Brady, 1997, for a critique). </p> <p> <bold> Double Deficit Theories. </bold> Lack of fluency in reading is a key characteristic of dyslexia, but there is extensive evidence of difficulties in speed of processing for almost all stimuli, including those for which sensory delay is an unlikely contributor. The earliest demonstrations derived from the Rapid Automatized Naming technique (Denckla &amp; Rudel, 1976), in which the child has to say the names on a page full of simple pictures (or colors). Children with dyslexia show robust speed deficits on these tasks. It has also been demonstrated that children with dyslexia are slower in their choice reaction to an auditory tone or a visual flash in the complete absence of phonological task components (Nicolson &amp; Fawcett, 1994). Even more direct data derives from an electroencephalography study (Fawcett et al., 1993) that established direct evidence of slowed auditory information processing for a pure tone, in that the P3 event-related potential wave was of longer latency in an oddball paradigm. A particularly interesting demonstration in the reading domain was provided by Yap and van der Leij (1993), who established that children with dyslexia needed a longer exposure time to read a known word than average achieving children matched for reading age. Recently, van der Leij and van Daal (1999) have argued, on the basis of speed limitations, that children with dyslexia have difficulty in automatizing word recognition skills and, furthermore, that this may lead to a strategy for processing large orthographic units in reading. Finally, in a synthesis of phonological and speed problems, Wolf and Bowers (1999) have proposed an alternative conceptualization of the developmental dyslexias, the double deficit hypothesis, which holds that phonological deficits and naming speed deficits represent two separable sources of reading dysfunction and that developmental dyslexia is characterized by both phonological and naming speed "core" deficits. </p> <p> <bold> The Cerebellar Deficit Hypothesis. </bold> In our longstanding research program, we attempted initially to characterize the symptoms of dyslexia from a learning perspective, leading to our automatization deficit hypothesis. In subsequent research, we subsumed this behavioral level hypothesis within the neurological level hypothesis of cerebellar deficit, as outlined below. </p> <p> <bold> The automatization deficit. </bold> In a series of studies in the early 1990s, Nicolson and Fawcett (1990, 1994, 1995a, 1995b) found that their panel of children with dyslexia showed severe deficits in a range of skills. These included balance (Fawcett &amp; Nicolson, 1992; Nicolson &amp; Fawcett, 1990; see also Yap &amp; van der Leij, 1994), although Wimmer, Mayringer, and Raberger (1999) offered an alternative explanation (i.e., attention-deficit/hyperactivity disorder, ADHD) for German-speaking children with dyslexia; motor skill (Fawcett &amp; Nicolson, 1995b; see also Haslum, 1989; Rudel, 1985; Wolff, Michel, &amp; Ovrut, 1990); phonological skill (Fawcett &amp; Nicolson, 1995a); and rapid processing (Fawcett &amp; Nicolson, 1994; Nicolson &amp; Fawcett, 1994). Furthermore, taking all the data together (Nicolson &amp; Fawcett, 1995a, 1995b), the majority of individual children with dyslexia showed problems across the board, rather than different children showing different profiles, as would be expected if there were a range of subtypes (Boder, 1973; Castles &amp; Holmes, 1996). This pattern of difficulties is consistent with the dyslexic automatisation deficit hypothesis (Nicolson &amp; Fawcett, 1990), which states that children with dyslexia will suffer problems in fluency for any skill that should become automatic via extensive practice. The hypothesis accounts neatly for the problems in acquiring phonological skills, reading skills, and noncognitive skills, but does not specify an underlying neurological structure. </p> <p> <bold> The cerebellar deficit hypothesis. </bold> Deficits in motor skill and automatization point strongly to the cerebellum, which has traditionally been considered a motor area (Eccles, Ito, &amp; Szentagothai, 1967; Holmes, 1917, 1939; Stein &amp; Glickstein, 1992) and is also claimed to be involved in the automatization of motor skills and in adaptive learning control via the cerebellar structures (Ito, 1984, 1990). For 10 years, there has been clear evidence that the cerebellum is also involved in language and cognitive skills (Allen, Buxton, Wong, &amp; Courchesne, 1997; Leiner, Leiner, &amp; Dow, 1989; Thach, 1996; see also the special issue of the Journal of Neurolinguistics, Vol. 13, 2000), including a recent demonstration of specific cerebellar involvement in reading (Fulbright et al., 1999). A cerebellar deficit, therefore, provides one parsimonious explanation of the range of problems suffered by children with dyslexia. We have recently established extensive multidisciplinary evidence directly consistent with the cerebellar deficit theory. First, we demonstrated (Nicolson, Fawcett, &amp; Dean, 1995) that children with dyslexia showed a dissociation, claimed by Ivry and Keele (1989) to be specific to patients with cerebellar damage, between time estimation and loudness estimation; second, we found that children with dyslexia showed a range of classic cerebellar signs (Fawcett &amp; Nicolson, 1999; Fawcett, Nicolson, &amp; Dean, 1996; see Note 1). A recent study also established unusually weak cerebellar activation when adults with dyslexia performed a motor sequence learning task (Nicolson et al., 1999). </p> <p>It is clear, therefore, that, at least for some children with dyslexia, cerebellar impairment provides a parsimonious account of the range of symptoms established by our earlier research. Moreover, the hypothesis provides a potentially unifying framework for dyslexia, because we note that cerebellar impairment would almost certainly give rise to articulatory difficulties and, thence, to phonological problems (see Heilman, Voeller, &amp; Alexander, 1996; Snowling &amp; Hulme, 1994; for advocacy of the latter link). Furthermore, a cerebellar deficit would lead to slowed central processing speed (see the double deficit hypothesis) and to deficits in motor skill, but not necessarily to sensory processing speed deficits. Space precludes a full analysis of the putative causal chain from early cerebellar impairment via articulation to phonological deficits to reading, spelling, and writing, the criterion measures for dyslexia. Suffice to say that reading is particularly severely impaired because it depends on two aspects of cerebellar function; first, learning new skills, and second, becoming expert in these skills; we have informally named this dual role for the cerebellum in reading the "double whammy" (for a review, see Nicolson &amp; Fawcett, 1999). </p> <hd id="AN0004192409-5"> Study Design </hd> <p>The aforementioned analyses provided the rationale for this study. As discussed, a stringent test of the adequacy of a theory of dyslexia is whether a similar pattern also arises for nondiscrepant poor readers (NDPR). In designing this study, we selected a range of tests for which the different theories made differential predictions. In brief, the aim of the study was to present selected tests from the range of tests developed by Nicolson and Fawcett (1994b) and Fawcett et al. (1996) to groups of children with NDPR and children with dyslexia. By examining the pattern of differences between groups and comparing with average achieving controls, we should be able to undertake a critical comparison of the different predictions. Our predictions for the different theories are given in Table 1. It should be noted that predictions for the different theories for dyslexia versus same-age controls are derived directly from the literature on the four causal models. Unfortunately, the literature on NDPR is relatively slight and somewhat variable, so in order to derive predictions for dyslexia versus same-age NDPR, it has been necessary to speculate somewhat about the NDPR performance. We propose tentatively that the NDPR group should have phonological problems (Aaron, 1997; Ellis et al., 1996), reduced speed of information processing (Vernon &amp; Mori, 1992), and mild motor difficulties (Ghaziuddin &amp; Butler, 1998). Fortunately, the NDPR data collected in this study may allow us to resolve this issue without the need for further speculation. </p> <hd id="AN0004192409-6">Method</hd> <hd1 id="AN0004192409-7"> Participants </hd1> <p>All children were drawn from two Sheffield local authority schools with a special unit for children with learning difficulties. To check for any changes in performance with age, the full intake from Grades 3 to 6 were tested-36 children in all, ages 7.3 to 11.1 years. Most had entered special education between 6 and 7 years of age. All these children were White, from middle to lower socioeconomic status families (social classes 3, 4, or 5). Children were tested blind, the experimenter having no knowledge of their IQ. After testing, psychologists' reports were accessed, which showed that the group contained children with IQ scores ranging from 68 to 130, with 29 out of 36 having IQ scores below 90. Children with IQ scores below 90 were allocated to the NDPR group, who would be classified in the United Kingdom as children with mild learning difficulties (see Note 2). These children with NDPR were divided into two age groups (see Table 2) to form an NDPR8 group (7-9 years; n = 14), and an NDPR10 group (10-11 years; n = 15). The composition of the NDPR group ranged from IQ 67 to 87, with only one child in each group having a discrepancy of 18 months or more between chronological age and predicted reading age. The majority of the children in each NDPR group read somewhat in advance of their predicted reading age, although behind the level appropriate for their chronological age. Children with IQ levels of at least 90 formed a small group with dyslexia (n = 7) with mean age around 8. This group was labeled D8-new. Because the number of children with dyslexia found in this group was low (see Note 3), for all analyses except the static cerebellar tests (see Table 5) they have been integrated with a group (n = 9) of 8-year-old children with dyslexia previously described in Fawcett et al. (1996). The overall group of children with dyslexia aged around 8 years is referred to as D8. Another group of 10-year-old children with dyslexia (D10) previously reported were also included in the analyses, as were data from two groups of control children aged around 8 and around 10 to 11 years, respectively (see Note 4). The latter groups are referred to as C8 and C10 respectively. All children had undertaken a full Wechsler Intelligence Scale for Children (WISC) intelligence test (Wechsler, 1976, 1992) together with the Wechsler Objective Reading Dimension (WORD) tests of reading and spelling (Wechsler, 1993). Children with dyslexia satisfied standard exclusionary criteria of children of average or above average IQ (operationalized as IQ equal or greater than 90), without known primary emotional, behavioral, or socioeconomic problems whose reading age (RA) was at least 18 months behind their chronological age (CA). Control children satisfied the same criteria, but were all reading within 6 months of their chronological age or better, with no history of reading problems. All children in the dyslexia and control comparison groups (Fawcett et al., 1996) were White, drawn from mixed socioeconomic status families (social classes 1-5), and also from the Sheffield area. In view of the known comorbidity of dyslexia with ADHD (Fletcher, Shaywitz, &amp; Shaywitz, 1999; Pennington, Groisser, &amp; Welsh, 1993; B. A. Shaywitz et al., 1995), and because of the suggestion that cerebellar problems in dyslexia may be attributable to an overlap with ADHD (Denckla, Rudel, Chapman, &amp; Krieger, 1985; Wimmer et al., 1999), all NDPR children were screened for ADHD by the psychologists at initial assessment using the Diagnostic and Statistical Manual of Mental Disorders (3rd revised edition; DSM-IIIR) scales (American Psychiatric Association, 1987; see Note 5). One child (in the NDPR8 group) showed clear evidence of attention-deficit disorder (ADD) together with behavioral problems (see Note 6). Only this child showed comorbid emotional and behavioral problems. One further child in the NDPR8 group had been diagnosed with dyspraxia. The results for the child with dyspraxia were included in the analysis, but the child with ADD was omitted. Psychometric details, including a breakdown by gender, chronological age, reading age, and IQ mean and range, are given in Table 2. </p> <hd1 id="AN0004192409-8"> Experimental Tasks </hd1> <p>A total of 17 tests were selected from those employed by Nicolson and Fawcett (1994a) and Fawcett et al. (1996). The selected tests covered the three major domains known to be affected in dyslexia, namely phonological processing (and verbal memory), rapid processing, and cerebellar tests. Clinical evidence of the range of deficits evident following gross damage to the cerebellum has been described in detail in classic texts by Holmes (1917, 1939) and Dow and Moruzzi (1958). Standard symptoms of cerebellar dysfunction are dystonia (problems with muscle tone) and ataxia (disturbance in posture, gait, or movements of the extremities). However, it should be noted that tests of this type typically involve a range of brain structures, and, in recognition of this, we describe these tests as cerebellar. The cerebellar tests were based directly on those described by Dow and Moruzzi, because standardized motor skill batteries do not capture the range of deficits associated with cerebellar abnormalities. The Dow and Moruzzi tests are clinically based and are somewhat dependent on clinical judgment. Consequently, considerable care was taken in the previous experiments to adapt the tests for experimental use, and, wherever possible, equipment was designed to facilitate fully objective procedures for each test. In previous research (Fawcett et al., 1996), children with dyslexia had been found to perform particularly poorly on these tasks. The cerebellar tests were divided further into tests for dystonia and ataxia. We refer to these more neutrally as static and dynamic cerebellar tests, respectively. It should of course be stressed that none of the tests in this battery can be simply ascribed to a single brain structure, and that abnormalities in a range of structures might potentially cause problems in any one of the tests. It is only by analysis of the pattern of difficulties on a range of tests that a potentially abnormal brain structure may be targeted. The test labels should therefore be seen as descriptive rather than diagnostic. Nevertheless, this does not bear significantly on the interpretation of the data, because these are standard clinical tests for cerebellar problems. If a child has cerebellar impairment, it should therefore show up on some of these cerebellar tests. Fuller descriptions of the cerebellar tests are given in Appendix 1, but, in short, the tests used were </p> <hd1 id="AN0004192409-9"> Static cerebellar tests </hd1> <p>Muscle tone--the ability to resist a push on the forearm. </p> <p>Arm displacement--the amount of disturbance caused by a gentle tap on the outstretched hands. </p> <p>Postural stability--the amount of disturbance from an upright stance when pushed gently in the back. </p> <p>Limb shake the wobbliness of each hand when shaken. </p> <hd1 id="AN0004192409-10"> Dynamic cerebellar tests </hd1> <p>Finger to thumb--speed of completing a series of 10 alternating oppositions of finger and thumb. </p> <p>Toe tapping--the time to tap the toes on the floor 10 times. </p> <p>Pegs--the time taken to transfer a row of 10 pegs from one row of a pegboard to the next row. </p> <p>Beads--the number of beads successfully threaded in 30 seconds. </p> <hd1 id="AN0004192409-11"> Tests of phonological processing and verbal memory </hd1> <p>Memory span--the mean for words of 1, 2, and 3 syllables, measured as the longest list of words that the participant can recall in the correct order. </p> <p>Segmentation--the Test of Auditory Analysis and Segmentation (Rosner &amp; Simon, 1971), in which the participant has to be able to break down a word into its phonemes, starting with easier tasks such as saying cowboy without the cow and moving to more difficult ones such as saying smack without the m. </p> <p>Rhyme--rhyme/sound categorization ability (a simplified version of the tests used in Bradley &amp; Bryant, 1983) for phonemes at the beginning and end of words, with representative questions being "Does cat rhyme with map?" and "Do map and man start with the same sound?" </p> <p>Nonword repetition--a test (Gathercole &amp; Baddeley, 1990) in which the participant has to repeat a nonsense word immediately after hearing it, with stimuli taken from a set of 40 ranging from 2 to 5 syllables (including bannow and versitrationist). </p> <p>Articulation time--time to articulate a single word (one fifth of the time for 5 repetitions). Mean of time for bus, monkey, and butterfly. </p> <hd1 id="AN0004192409-12"> Tests of processing speed </hd1> <p>Word flash--score on reading a series of words, where each word is presented for a shorter duration, starting with 17 one-syllable words--dog for 1 second down to bat for 16 ms, followed by 11 two-syllable words--water for 500 ms down to leather for 100 ms. There were 10 nonalphabetical stimuli interspersed within the sequence. Participants had to say whether it was a word and, if so, what it was. </p> <p>Simple auditory reaction time--median response latency for pressing a button on hearing a 350 Hz tone. </p> <p>Selective auditory Choice Reaction Time--median response latency for pressing a button on hearing a 350 Hz tone in the context of an equally probable 1400 Hz tone to which no response must be made. </p> <p>Visual search--the time taken to locate a distinctive spotty dog on each of several crowded pages in a child's puzzle book. </p> <hd1 id="AN0004192409-13"> Procedure </hd1> <p>Children were tested individually. A detailed protocol for each test had been developed previously and was kept to as closely as possible. The experimenters were blind to participant status in all tests until after the data were collected. Generalized reassurance ("Well done," "that was a bit tricky," etc.) was given throughout, but no comparative comments were made on the quality of each child's performance. Testing was completed over three sessions in the course of 1 month, with each session taking about 30 minutes overall. Tests were administered in random order within the sessions, to avoid the possibility of order effects. Owing to unforeseen circumstances, the NDPR10 group did not undertake two tests (word flash and selective auditory choice reaction time). Furthermore, the static cerebellar tests had not been administered to the original 8-year-old group with dyslexia. Consequently, all static tests for the D8 group derive from the D8-new group. </p> <hd id="AN0004192409-14">Results</hd> <p>The means and standard deviations for the battery of tests are presented in Table 3. It may be seen that both the children with NDPR and the children with dyslexia performed less well than the age-matched controls on the majority of the tests. </p> <p>A series of two-factor analyses of variance was undertaken separately for each task, with the factors being group/disability type (NDPR, dyslexia, or control) and age (2 levels; see Note 7). A summary of these analyses is presented in Table 4. For all but 2 of the 17 tasks (toe tapping and articulation time) the effect of age was not significant. In only one task (arm displacement) was there a significant interaction between age and disability type. By contrast, there was a significant effect of disability type in all 17 tasks (see Note 8). When the type main effect was significant, Fisher protected LSD a posteriori analyses were undertaken to establish which of the three disability types differed significantly, and these findings are also given in Table 4. Compared with the NDPR group, the controls performed significantly better on all 17 tasks except the four static cerebellar tasks and articulation rate. Compared with the group with dyslexia, the controls performed significantly better on all four static cerebellar tests, four out of five phonological tests (excluding memory span), one speed test (word flash), and three dynamic cerebellar tests (finger to thumb, toe tapping and beads). The group with dyslexia performed significantly better than the group with NDPR on four out of five phonological tests (excluding articulation rate, for which the group with dyslexia was near-significantly slower, p less than .07, than the group with NDPR), two speed tests (word flash and simple reaction), and one of the dynamic cerebellar tests (toe tapping). The group with NDPR performed significantly better than the group with dyslexia on all four static cerebellar tasks. </p> <hd1 id="AN0004192409-15"> Effect Size Analyses </hd1> <p>Effect size analyses (e.g., Cohen, 1969) were used to facilitate comparison between the tests and to elucidate the patterns of results (Loftus, 1996). The data for each test for each disability type and age were first normalized relative to the data for the corresponding control group. For example, for the D8 group the data for postural stability for each participant were normalized by obtaining the difference of that participant's postural stability score from the mean postural stability score for group C8 and then dividing this difference by the standard deviation of the C8 group for postural stability. Groups NDPR8 and D8 were normalized relative to C8, and groups NDPR10 and D10 were normalized relative to C10. The sign was adjusted such that a negative effect size indicated below-average performance. This procedure led to an age-appropriate effect size in standard deviation units (analogous to a z score) for each test for each child. Comparison of effect size magnitudes between tasks gives an index of which tasks prove the most problematic for the children with dyslexia and the children with NDPR, although it should be noted that the small numbers of children involved per group limit the precision of the analyses. The effect sizes (averaged across the two ages) for the different tasks for NDPR and dyslexia are shown graphically in Figure 1. Performance at control level would have a zero effect size, an effect size of-1 indicates performance one standard deviation of the controls below the control level, and so on. As a rule of thumb, an effect size of -2 or worse is likely to indicate a significant deficit compared with control performance. </p> <p>It may be seen that a clear dissociation is present. For the majority of tasks, the children with NDPR did somewhat worse than the children with dyslexia (significantly in 5 out of 17 cases, as indicated by the first column of Table 4). This is true in the main for the phonological tasks (with NDPR significantly worse than dyslexia in memory span, segmentation, and rhyme), for the speed of processing tasks (with NDPR significantly worse than dyslexia for the word flash task), and for the dynamic cerebellar tasks (with NDPR significantly worse than dyslexia for toe tapping). By contrast, for the static cerebellar tasks, the children with NDPR performed close to average and significantly better than the children with dyslexia on all four tasks. </p> <hd1 id="AN0004192409-16"> Individual Effect Size Analyses </hd1> <p>The aforementioned analyses indicate a pattern of dissociation in specific tests at the group level between the group with dyslexia and the groups with NDPR--the groups with dyslexia tend to do relatively well on simple reaction time and memory span and relatively badly on the static cerebellar tests. The groups with NDPR do badly on the speed tests and well on the static cerebellar tests. A key question is the extent to which these differential group patterns apply also at the level of the individual. Consequently, a further set of individual analyses was undertaken, in which effect sizes relative to the age-appropriate control group were calculated for each child. Tests were also aggregated into four groups: static cerebellar, dynamic cerebellar, phonological, and speed. Two analyses are reported on these data. Analysis 1 averages the effect sizes per test group and determines at-risk incidence per test group for each participant, with "at risk" defined first in terms of p less than .05 one-tailed (z less than -1.28) and also at the stricter criterion of p less than .01 one-tailed (z less than -2.05). Analysis 2 determines the at-risk incidence differently, by calculating whether the child is significantly at risk (p less than .05) on at least half of the tests in the test group. The results are presented in Table 5. For this analysis the D8 children from the current study (n = 7) have been disaggregated from the children with dyslexia from our previous analyses because we already knew that the latter showed difficulties with static cerebellar tests. </p> <p>It may be seen that for the two groups with NDPR, there is a very high percentage of significant deficits on dynamic cerebellar, phonological, and speed tests. Taking the two groups with NDPR together, 30 out of 30 (100%) were significantly (p less than .05) impaired on dynamic cerebellar tests, with 27 out of 29 (93%) significantly impaired on phonological tests, and 28 out of 29 (97%) significantly impaired on speed tests. By contrast, only 8 out of 28 (29%) were impaired (p less than .05) on static cerebellar tests. Only 3 out of 28 (10%) were highly significantly impaired (p less than .01) on the static cerebellar tests. Close to 100% of the children with NDPR were significantly impaired on at least half of the component tests making up the dynamic, phonological, and speed test groups, with only 40% for the static cerebellar test group. </p> <p>For the children with dyslexia, a different pattern emerges. Taking them as a whole, the greatest proportion (79%) show a significant (p less than .05) deficit on the static cerebellar tests, with 74%, 53% and 53% deficits for the dynamic cerebellar, phonological, and speed tests, respectively. The picture is slightly less clear for the new D8 group, for whom only 3 out of 7 (43%) showed a significant deficit on the static cerebellar tests. The proportions of deficit on at least half the component tests were considerably higher, with the percentages for all the children with dyslexia being 95%, 71%, 82%, and 50% for the static cerebellar, dynamic cerebellar, phonological, and speed tests, respectively. For the new D8 group, all but one child (KN; 86%) were impaired on at least half the static cerebellar tests. Accessing the psychometric records of the children with dyslexia indicated that KN had a dyslexia/NDPR diagnosis, as did one of the other six children with dyslexia. Inspection of the individual data for the new D8 group indicated that KN had an IQ of 90--right on the borderline between NDPR and dyslexia. Her performance showed a profile very typical of NDPR (effect sizes 0.08, -1.63, -2.68, and -2.37 for the static cerebellar, dynamic cerebellar, phonological, and speed tests, respectively). </p> <p>The groups with NDPR, in contrast with the groups with dyslexia, showed no particular pattern of association with static cerebellar test performance. Six children with NDPR showed impairment on more than half the static cerebellar tests. Their IQs were 68, 71, 71, 72, 81, and 82, respectively. Accessing the psychometric records of the children involved indicated that four of the six had been given a diagnosis of NDPR/dyslexia and had a distinctly spiky profile of scores on the WISC-R subtests (see Note 9), unlike the flatter profile of those who had been given an unequivocal NDPR diagnosis. Only 5 of the remaining 24 children with NDPR had been given a mixed diagnosis, with the remainder having a definite NDPR diagnosis. Clearly, therefore, there was something about this group of children with NDPR with poor static cerebellar performance that suggested dyslexia as well as NDPR. It seems likely, therefore, that the groups with NDPR are not homogeneous and that some of the children with NDPR show signs both of mild learning difficulties and of dyslexia. It would be appropriate to undertake a separate analysis for the groups with signs of both NDPR and dyslexia, but there are not enough children in each group to make this approach viable in this study. </p> <p>A striking feature reported by the experimenter (FM) from her notes is that the children with dyslexia showed a qualitative difference from the children with NDPR on the static tasks. Naturally, the experimenter was blind to participant status during testing, but her informal observations of the children suggested that children with dyslexia showed a characteristic pattern of low muscle tone or hypotonia, evident from their posture as well as their limb control. For example, the brightest child with dyslexia (IQ 130) tried to shift his balance backwards to compensate in the postural stability task, leading him to stumble backwards and, thus, generate a higher score. By contrast, most of the children with NDPR showed a much more controlled and solid stance. Similarly, the toe tap of the NDPR group was typically steady and measured, leading to the speculation that these children were unable to initiate the requisite motor program quickly. The children with dyslexia, by contrast, were more variable in their output, producing an initial flurry of toe taps interspersed with pauses. </p> <hd1 id="AN0004192409-17"> Correlations with Discrepancy </hd1> <p>It should be noted that the aforementioned analyses have defined groups merely in terms of the IQ cutoff of 90, and have not investigated directly the magnitude of the discrepancy between observed reading age and reading age expected on the basis of IQ. To investigate directly which of the tests do appear to be associated with the concept of discrepancy, a further analysis was undertaken in which the correlation between each task and discrepancy, defined here as difference between reading age and "mental age" (i.e., chronological age x IQ/100) was calculated (see Note 10). The correlations are shown in Table 6, with the sign adjusted such that a positive correlation indicates that better performance goes with greater discrepancy. It may be seen that the correlations are in the main positive, reflecting the fact that the children with NDPR (who have low discrepancy) perform worse than the children with dyslexia (who have high discrepancy). The two highest correlations are for simple reaction time (0.594) and word flash (0.542). Other tests with high correlations (accounting for at least 20% of the variance) are toe tap (0.419) and memory span (0.473). By contrast, five tasks have a negative correlation, namely the four static cerebellar tests together with articulation rate, with the most negative correlation being arm displacement (-.449). </p> <p>There is a clear positive correlation between discrepancy and chronological age (r = .291, p less than .05), indicating that discrepancy increases with age. This Matthew Effect is a factor highlighted by a number of researchers following Stanovich (1986). Consequently, further partial correlation analyses were undertaken to eliminate chronological age. It may be seen (Table 6, column 3) that this somewhat reduces the correlations for the speed tests and the dynamic cerebellar tests (as expected) but has relatively slight effect on the static cerebellar tests and the phonological tests. </p> <p>Overall, therefore, the correlational analyses further support the between-group and individual analyses in identifying a dissociation between the NDPR and dyslexia groups between the static cerebellar tests and the other tests. This dissociation obtains even when the effects of age are partialed out. </p> <hd id="AN0004192409-18">Discussion</hd> <p>The major objective of this study was to compare the performance of children with NDPR, children with dyslexia, and average achieving controls of the same age. The performance of the groups with NDPR was significantly poorer than that of the groups with dyslexia on two of four speed tests, four of five phonological tests, and one of four dynamic cerebellar tests, with worse mean performance on all the remainder (except articulation rate). By contrast, a dissociation was observed in that the performance of the groups with NDPR on all four of the static cerebellar tasks was significantly better than that of the groups with dyslexia. </p> <p>It remains to consider the theoretical significance of these results. In the introduction, we outlined the predictions of five major classes of causal theory for dyslexia (see Table 1). The results (averaged across the different tasks in each category) are presented in Table 7 (see Note 11). If we consider only the results for the children with dyslexia compared with the chronological age-matched controls, only the double deficit and cerebellar deficit hypotheses correctly predict more than two of the five results. The cerebellar deficit hypothesis is excellent in prediction, in that the only failure is an unfulfilled prediction of deficit on auditory processing speed. </p> <p>Turning to the predicted differences compared with the NDPR groups, it is again evident that most of the theories are inaccurate in their predictions. Only the cerebellar deficit hypothesis predicts more than two of the five outcomes correctly. All the remainder make at least one dearly disconfirmed prediction (predicting significantly better when the results indicate significantly worse or vice versa). A crude scoring system, giving +2 for *[this character cannot be represented in ASCII text], 1 for *[this character cannot be represented in ASCII text], -1 for X, and -2 for XX, leads to a score of +9 for the cerebellar deficit hypothesis and negative scores for the remainder. Moving to the pattern of results, and in particular the dissociation obtained, only the cerebellar deficit predicts this dissociation. It is clear, therefore, that the data provide strong support, both quantitatively and qualitatively, for the cerebellar deficit hypothesis compared with the other extant hypotheses. </p> <p>The dissociation between static and dynamic cerebellar tests for these NDPR groups may indicate that the abnormalities for the children with dyslexia lie within the lateral parts of the posterior lobe of the cerebellum, because lesions in this area are often associated (Holmes, 1922) with dysmetria (inaccurate limb movement) and hypotonia (low muscle tone). These findings are particularly interesting in view of recent findings of abnormal activation patterns in the ipsilateral posterior lobe of the cerebellum of adults with dyslexia, both when executing a previously overlearned motor sequence task and when learning a new motor sequence (Nicolson et al., 1999). </p> <p>An important methodological issue relates to the static cerebellar tests. These tests were derived from the classic clinical cerebellar tests (Dow &amp; Moruzzi, 1958), but it must be noted that such tests are notoriously difficult to operationalize and quantify. Furthermore, unlike most of the other tests, these tests involve direct interaction with the experimenter and may therefore raise issues of socialization and personal space. In parallel research as part of an extensive screening battery (Fawcett &amp; Nicolson, 1996), we have developed a more objective and more easily quantified index of balance, using a specially designed postural stability tester that allows the experimenter to push the small of the participant's back with a metered force. Furthermore, in recent research (Nicolson et al., 1999) we undertook a brain imaging study on young adults with dyslexia in whom we had previously established evidence of problems on the static cerebellar tests. These participants showed, on average, only 10% of normal cerebellar activation on a motor sequence learning task known typically to involve strong cerebellar activity. Consequently, in addition to the strong clinical evidence, there is evidence that these static cerebellar tests do provide a valid index of cerebellar abnormality. Nonetheless, development of objective and simple static cerebellar tests remains an important research priority. </p> <p>Despite the clarity of the results obtained here, it is important to note the limitations of the current study. First and foremost, the number of participants was not large, and further studies would need to be undertaken in order to fully address the generality of the results. Second, although a wide range of tests was undertaken, tests sensitive to magnocellular deficit were not undertaken, so it is possible that some, or even all, of the children with dyslexia would show a magnocellular deficit (visual or auditory). We can be sure, however, that, at least for these participants with dyslexia, there were cerebellar deficits over and above any hypothetical sensory deficit. Third, there was not a complete dissociation between children with and without discrepancy on the static cerebellar tests. It is likely that some children with NDPR also have a cerebellar deficit. The incidence of comorbidity in the present study was 20%--well above the prevalence of dyslexia in the general population. </p> <hd id="AN0004192409-19">Conclusions</hd> <p>This study was intended to establish whether poor readers with IQ discrepancy (children with dyslexia) can be distinguished from poor readers with no IQ discrepancy (NDPR) using a range of tests of skills known to be impaired in children with dyslexia. A dissociation was established between the groups with dyslexia and the groups with NDPR. Most children with NDPR performed at near-average levels on static cerebellar tests and also performed significantly better than children with dyslexia on these tests. By contrast, children with NDPR showed problems equivalent to or significantly greater than children with dyslexia on dynamic cerebellar tests, on phonological and verbal memory tests, and on speed of processing tests. These findings provide evidence of the generality of phonological and speed deficits in both NDPR and dyslexia, compared with the specificity of static cerebellar tests of muscle tone and stability deficits in dyslexia. </p> <p>These results cast doubt on the ability of sensory processing hypotheses to account for the range of problems in dyslexia and suggest rather that sensory processing deficits, where they occur, are more likely to be subtypes than core deficits for dyslexia. The results are also inconsistent with the pure phonological deficit hypothesis and the pure double deficit hypothesis. It should be stressed, however, that the results do not disconfirm these two hypotheses--indeed, in comparing children with dyslexia and age-matched average achieving children, clear deficits were obtained in both phonological and speed tasks. Rather, the pattern of results indicates, first, that these hypotheses in and of themselves are not sufficient to account for the pattern of difficulties found in dyslexia, and, second, that the "core" deficits predicted by these theories are not sufficient to distinguish between children with dyslexia and children with NDPR. By contrast, the cerebellar deficit hypothesis, which predicts phonological and speed deficits in addition to cerebellar deficits for the children with dyslexia, gave an excellent account of the results obtained and did correctly predict the dissociation between the children with dyslexia and the children with NDPR on cerebellar tasks. </p> <p>In conclusion, from a theoretical viewpoint, this study suggests that there are differences between the phenotypes of children with dyslexia and children with more generalized learning difficulties. Although we may well expect some overlap between the two groups, these results suggest that the majority of children with dyslexia suffer from a mild cerebellar deficit in static tests, whereas the majority of children with NDPR do not. Naturally enough, these results need to be replicated with further groups of children with dyslexia and children with NDPR. The dissociation between cerebellar tests and phonological tests for these groups provides further strong support for the cerebellar deficit hypothesis (Nicolson et al., 1995). Furthermore, regardless of the specific interpretation made, the dissociation obtained in this study between children with NDPR and children with dyslexia demonstrates that there are indeed theoretically valid reasons for distinguishing between poor readers with IQ discrepancy and those without. </p> <hd1 id="AN0004192409-20"> AUTHORS' NOTES </hd1> <p>1. The research on which this article was based partially supported by grant 8-04-43189 from the Medical Research Council to the University of Sheffield. </p> <p>2. We would like to thank Bluestone Junior School and Southey Green Junior School for access to their Special Needs Units. </p> <hd1 id="AN0004192409-21"> NOTES </hd1> <p>1. It should be noted that children with ADHD may also show evidence of cerebellar deficit (Denckla et al., 1985; Wimmer et al., 1999), but this may reflect the overlap between dyslexia and ADHD of around 30% (Fletcher et al., 1999; Pennington et al., 1995; B. A. Shaywitz et al., 1995). </p> <ulist> <item>2. The terminology and also the criterion vary between countries. In the United Kingdom, the cutoff for this group is IQ below 90, whereas in the United States a cutoff of 85 is open used. In fact, only one NDPR child (NDPRIO group) had an IQ greater than 85, so in this study the difference is not important. </item> <item>3. It is unfortunate that only 7 of the children tested had dyslexia, as opposed to 29 without discrepancy. It indicates the lack of control inherent in a blind study of this type, where one does not access the psychometric data until after the experiment. On the other hand, we knew what the pattern of results for children with dyslexia was likely to be, having already tested about 100 children on this type of test, and this group followed the same pattern. The new data derive from the 29 children without dyslexia, and it is these data that form the major strength of the findings. In short, the small numbers with dyslexia were a limitation, but they do not constitute a problem in terms of interpretation, given the extensive previously published evidence. </item> <item>4. Many of the additional control children and children with dyslexia had undertaken the cerebellar tests at a later time than the other tests. Only children who had taken a given test at the appropriate time for inclusion within the appropriate age group were included in the analyses. Consequently, the numbers and constituents of the control and dyslexia groups vary between the different tests. Data from these children was reanalyzed for this study. The dyslexia and control group children reported previously were not retested for this study because they were no longer matched for age. </item> <item>5. The DSM-IIIR assessment for ADHD involves 14 simple yes/no questions, with a yes on at least 8 being the minimal criterion for diagnosis of weak ADHD. It should be noted that the incidence of ADHD in the United Kingdom is currently low (ca. 0.5%, Reason, 1999). </item> <item>6. This child showed many signs of ADHD, but in the United Kingdom at this stage ADD was more usually diagnosed. </item> <item>7. The analyses of variance lacked one group (NDPR10) for two tasks, as can be seen from Table 3. In these cases, the appropriate statistics were computed for the five remaining groups. </item> <item>8. It is common practice in the case of multiple analyses of variance to apply the Bonferroni correction to take account of the possibility of the odd significant difference arising by chance. This was not appropriate in the present study, given that every analysis led to a significant difference. </item> <item>9. A dyslexia profile has been associated with a distinctive pattern on the WISC tests, the so-called ACID profile, with specific deficits in digit span and coding in relation to the remaining scores. This profile has led the educational psychologist working with these children to a diagnosis of dyslexia-type difficulties in the presence of low IQ. </item> <item>10. It should be noted that this simplistic expectancy formula ignores the dilution of the expected discrepancy caused by the imperfect correlation between IQ and reading, together with issues such as measurement error. The regression discrepancy model (Reynolds, 1984), which explicitly accounts for these factors, suffers from the drawback that estimated population correlations between ability and reading need to be entered. It is not clear that this is an appropriate procedure for either of the special populations under study here. </item> <item>11. We acknowledge that the visual deficit hypotheses are not done full justice by this analysis, insofar as we were not able to use tasks for which one might predict a specific deficit for the children with dyslexia. Nonetheless, there are clear deficits on tasks for which the visual deficit hypotheses would predict no discrepancy. </item> </ulist> <hd id="AN0004192409-22">TABLE</hd> <p>1 Outline Predictions for the Different Theories for Dyslexia on the Range of Tasks Administered </p> <ct id="AN0004192409-23"> Legend for Chart: A - Measure B - Phonological deficit C - Speed deficit D - Visual deficit E - Auditory deficit F - Double deficit G - Cerebellar deficit A B C D E F G Dyslexia vs. control Phonological [a] [c] [c] [c] [a] [b] Motor [c] [b] [c] [c] [b] [b] Visual speed [c] [a] [c] [c] [a] [c] Auditory speed [c] [a] [c] [a] [a] [b] Cerebellar [c] [c] [c] [c] [c] [a] Dyslexia vs. NDPR Phonological [b] [c] [c] [c] [a] [c] Motor [c] [d] [c] [c] [c] [c] Visual speed [d] [b] [c] [d] [b] [c] Auditory speed [d] [b] [c] [b] [b] [c] Cerebellar [c] [c] [c] [c] [c] [b]</ct> <p>Note. Predictions for the NDPR group are based on the assumption that they will show some phonological, motor, and speed deficits compared with same-age average achieving children. </p> <p>a = very significantly impaired; b = significantly impaired; c = roughly equivalent; d = significantly better </p> <hd id="AN0004192409-24">TABLE 2</hd> <p>Psychometric Data for Study Participants and Comparison Groups </p> <ct id="AN0004192409-25"> Legend for Chart: A - Group B - n, Total C - n, Boys D - n, Girls E - IQ (WISC-R/BAS), M F - IQ (WISC-R/BAS), range G - Chronological age, M H - Chronological age, range I - Reading age, M J - Reading age, range A B C D E F G H I J D8-new 7 6 1 103.3 90-130 8.28 7.7-9.1 6.52 5.8-8.7 NDPR8 15 9 6 75.8 68-84 8.02 7.3-9.2 6.31 5.1-7.5 NDPR10 14 11 3 77.2 67-87 10.32 9.5-11.1 7.91 5.9-10.8 D8-overall 16 13 3 107.0 90-133 8.19 7.7-9.1 6.66 5.6-8.7 D10 15 12 3 111.6 96-133 10.70 10.2-11.0 8.1 7-9.9 C8 20 17 3 119.3 91-141 8.48 7.0-9.4 11.16 7.7-13.3 C10 13 10 3 112.6 92-135 11.0 10.1-12.1 12.49 10.0-17</ct> <p>Note. The groups of children with NDPR are labeled NDPR8, NDPR10, with the suffix indicating the mean age. The group of children who were identified as having dyslexia in this study are labeled D8-new. Participants with dyslexia were augmented with existing data for children with dyslexia, leading to the creation of two further groups, D8-overall and D10. Two control groups, C8 and C10, have also been added for comparative purposes. The data for groups D8, D10 and C8, C10 were reported in Fawcett et al. (1996). WISC-III = Wechsler Intelligence Scale for Children (Wechsler, 1992). BAS = British Ability Scales (Elliott, 1983). WORD = Wechsler Objective Reading Dimension (Wechsler, 1993). </p> <hd id="AN0004192409-26">TABLE 3</hd> <p>Summary of Mean Scores for Each Group on Each Test </p> <ct id="AN0004192409-27"> Legend for Chart: A - Task B - NDPR8: M C - NDPR8: SD D - NDPR10: M E - NDPR10: SD F - D8: M G - D8: SD H - D10: M I - D10: SD J - C8: M K - C8: SD L - C10: M M - C10: SD A B C D E F G H I J K L M Postural stability (max. 12) 3.73 2.79 4.00 3.61 7.43 3.82 9.00 3.13 2.25 2.26 1.00 2.12 Limb shake (max. 3) 1.87 0.64 1.83 0.72 2.00 0.71 2.63 0.52 1.64 0.39 1.12 0.44 Arm displacement (max. 12) 1.80 1.37 1.39 1.12 3.00 1.53 3.83 0.58 1.57 0.79 0.50 0.93 Muscle tone (max. 6) 2.20 2.43 0.77 1.64 3.14 2.34 3.92 2.71 1.43 0.79 0.38 0.74 Finger to thumb (s) 30.2 14.0 23.3 9.80 25.2 13.4 17.6 12.3 7.65 1.46 9.27 2.96 Toe tapping (s) 3.89 0.74 3.90 0.79 3.54 0.44 2.82 0.71 2.44 0.41 2.04 0.34 Beads (total) 8.07 2.40 9.78 1.56 9.29 2.56 10.0 1.87 12.0 1.23 12.4 3.85 Pegs (s) 14.8 3.80 13.2 1.64 14.1 2.82 11.9 4.14 10.5 1.29 10.3 1.50 Segmentation (max. 13) 5.73 2.43 4.44 2.70 7.29 3.86 9.40 2.30 10.9 1.20 12.8 0.50 Rhyme (max. 30) 26.1 2.30 24.4 2.56 27.2 2.15 28.6 1.14 29.5 1.04 29.8 0.45 Memory span 3.17 0.68 2.93 0.55 3.81 0.81 4.32 0.27 4.24 0.49 4.52 0.64 Nonword repetition (%) 60.3 15.9 71.7 7.3 73.7 15.8 72.1 5.48 83.3 5.45 86.4 7.89 Articulation time (s) 0.51 0.12 0.44 0.08 0.56 0.13 0.45 0.08 0.46 0.05 0.36 0.05 Word flash[a] (max. 38) 22.5 4.02 -- -- 30.1 6.67 33.2 5.81 36.5 0.97 37.6 0.89 Visual Search (s)[a] 23.1 8.78 -- -- 21.2 12.0 15.0 8.32 13.5 6.48 8.92 3.11 Simple reaction time (cs) 52.1 26.5 54.4 16.4 48.3 12.2 34.1 6.61 40.0 7.55 33.4 5.80 Selective CRT (cs) 88.9 27.0 73.56 13.9 71.0 32.0 65.9 22.5 60.6 17.0 45.7 7.70</ct> <p>Note. NDPR8 = nondiscrepant poor reading, mean age 8. NDPR10 = nondiscrepant poor reading, mean age 10. D8 = dyslexia, mean age 8. D10 = dyslexia, mean age 10. C8 = control, mean age 8. C10 = control, mean age 10. CRT = choice reaction time. </p> <p>a The group NDPR10 did not undertake these tests. </p> <hd1 id="AN0004192409-28"> TABLE 4 </hd1> <p>Inferential Statistics for Chronological Age and Disability Type </p> <ct id="AN0004192409-29"> Legend for Chart: A - Task B - Group C - Age D - Interaction A B C D Postural stability F(2,61) = 22.7, p is less than .0001 C is greater than D, NDPR is greater than D F(1,61) = 0.03, ns F(2,61) = 1.2, ns Limb shake F(2,54) = 8.8, p is less than .001 C is greater than D, NDPR is greater than D F(1,54) = 0.1, ns F(2,54) = 3.0, ns Arm displacement F(2,56) = 22.0, p is less than .0001 C is greater than D, NDPR is greater than D F(1,56) = 0.5, ns F(2,56) = 3.2, p is less than .05 Muscle tone F(2,56) = 7.9, p is less than .001 C is greater than D, NDPR is greater than D F(1,56) = 1.1, ns F(2,56) = 1.6, ns Finger to thumb F(2,54) = 14.2, p is less than .0001 C is greater than NDPR, C is greater than D F(1,54) = 2.2, ns F(2,54) = 1.0, ns Toe tapping F(2,54) = 13.6, p is less than .0001 C is greater than D, C is greater than NDPR, D is greater than NDPR F(1,54) = 4.3, p is less than .05 F(2,54) = 1.6, ns Beads F(2,44) = 8.8, p is less than .001 C is greater than NDPR, C is greater than D F(1,44) = 1.9, ns F(2,44) = 0.5, ns Pegs F(2,44) = 6.8, p is less than .01 C is greater than NDPR F(1,44) = 2.2, ns F(2,44) = 0.9, ns Segmentation F(2,44) = 29.2, p is less than .0001 C is greater than D, C is greater than NDPR, D is greater than NDPR F(1,44) = 1.4, ns F(2,44) = 2.5, ns Rhyme F(2,49) = 22.6, p is less than .0001 C is greater than D, C is greater than NDPR, D is greater than NDPR F(1,49) = 0.01, ns F(2,49) = 2.9, ns Memory span F(2,51) = 24.6, p is less than .0001 C is greater than NDPR, D is greater than NDPR F(1,51) = 1.2, ns F(2,51) = 1.9, ns Nonword repetition F(2,60) = 12.7, p is less than .0001 C is greater than D, C is greater than NDPR, D is greater than NDPR F(1,60) = 2.0, ns F(2,60) = 1.8, ns Articulation time F(2,61) = 4.6, p is less than .05 C is greater than D F(1,61) = 13.6, p is less than .001 F(2,61) = 0.3, ns Word flash[a] F(2,37) = 33.9, p is less than .0001 C is greater than NDPR, C is greater than D, D is greater than NDPR F(1,37) = 1.6, ns F(1,37) = 0.3, ns Visual Search[a] F(2,36) = 3.9, p is less than .05 C is greater than NDPR F(1,36) = 2.5, ns F(1,36) = 0.6, ns Simple reaction time F(2,60) = 5.9, p is less than .01 C is greater than NDPR, D is greater than NDPR F(1,60) = 2.0, ns F(2,60) = 1.5, ns Selective CRT F(2,50) = 7.0, p is less than .01 C is greater than NDPR F(1,50) = 3.5, ns F(1,42) = 0.3, ns</ct> <p>Note. C = control group. NDPR = nondiscrepant poor reading group. D = dyslexia group. CRT = choice reaction time. </p> <p>a The group NDPR10 is not included in these analyses. </p> <hd id="AN0004192409-30">TABLE 5</hd> <p>Percentage of Individual At-Risk Scores for the Four Test Types </p> <ct id="AN0004192409-31"> Legend for Chart: A - Group B - Significance level C - Test type: Static cerebellar D - Test type: Dynamic cerebellar E - Test type: Phonological F - Test type: Speed A B C D E F NDPR8 p is less than .05 26.67 100.00 p is less than .01 13.33 93.33 greater than or equal to 50% 33.33 100.00 93.33 100.00 80.00 100.00 100.00 100.00 NDPR10 p is less than .05 30.77 100.00 p is less than .01 7.69 86.67 greater than or equal to 50% 46.15 100.00 92.86 92.86 78.57 78.57 92.86 92.86 D8-new p is less than .05 42.86 100.00 p is less than .01 42.86 0.00 greater than or equal to 50% 85.71 100.00 33.33 66.67 16.67 66.67 66.67 66.67 D8-overall p is less than .05 42.86[a] 71.43 p is less than .01 42.86[a] 57.14 greater than or equal to 50% 85.71[a] 100.00 53.33 53.33 33.33 53.33 66.67 66.67 D10 p is less than .05 100.00 58.82 p is less than .01 91.67 35.29 greater than or equal to 50% 100.00 64.71 71.43 57.14 42.86 42.86 100.00 57.14</ct> <p>Note. NDPR8 = nondiscrepant poor reading, mean age 8. NDPR10 = nondiscrepant poor reading, mean age 10. D8-new = dyslexia, mean age 8, new participants only. D8-overall = dyslexia, mean age 8, combined new and original (Fawcett et al., 1996) groups. D1 = dyslexia, mean age 10. </p> <p>a The original D8 group did not undertake the static cerebellar test, so these scores derive only from the D8-new group. </p> <hd id="AN0004192409-32">TABLE 6</hd> <p>Correlations with IQ/Reading Age Discrepancy </p> <ct id="AN0004192409-33"> Correlation (NDPR/dyslexia) Task Full Partial Postural stability -.218 -.211 Limb shake -.244 -.266 Arm displacement -.449[b] -.442 Muscle tone -.179 -.277 Finger to thumb .335[a] .318 Toe tapping .419[b] .395 Beads .513[b] .094 Pegs .261 .071 Segmentation .361[a] .354 Rhyme .295 .314 Memory span .473[b] .208 Nonword repetition .400[b] .339 Articulation time .115 .243 Word flash .542[a] .180 Visual Search .227 .143 Simple reaction time .594[c] .564 Selective choice reaction time .252 .055</ct> <p>Note. The analysis is limited to participants in the groups with NDPR and the groups with dyslexia. Signs of correlations have been determined such that a positive correlation indicates that improved performance goes with increased discrepancy. The partial correlations involve the elimination of the effect of chronological age. </p> <p>c p is less than .001. </p> <p>b p is less than .01. </p> <p>a p is less than .05. </p> <hd id="AN0004192409-34">Table 7</hd> <p>Comparison of Results with the Predictions of the Different Theories </p> <ct id="AN0004192409-35"> Legend for Chart: A - Measure B - Phonological deficit: Prediction C - Phonological deficit: Outcome D - Speed deficit: Prediction E - Speed deficit: Outcome F - Visual deficit: Prediction G - Visual deficit: Outcome H - Auditory deficit: Prediction I - Auditory deficit: Outcome J - Double deficit: Prediction K - Double deficit: Outcome L - Cerebellar deficit: Prediction M - Cerebellar deficit: Outcome N - Comparison A B C D E F G H I J K L M N Dyslexia vs. control Phonological 1 5 3 7 3 7 3 7 1 5 2 5 9 Motor 3 7 2 5 3 7 3 7 2 5 2 5 2 Visual speed 3 7 1 5 3 7 3 7 1 5 2 5 9 Auditory speed 3 6 1 7 3 6 1 7 1 7 2 7 9 Cerebellar 3 7 3 7 3 7 3 7 3 7 1 5 2 Dyslexia vs. NDPR Phonological 2 8 3 7 3 7 3 7 2 7 3 7 9 Motor 3 5 4 7 3 6 3 6 3 6 3 6 3 Visual speed 4 5 2 8 3 7 4 6 2 7 3 7 4 Auditory speed 4 7 2 7 3 6 2 7 2 7 3 6 3 Cerebellar 3 7 3 7 3 7 3 7 3 7 2 5 2</ct> <p>Note. </p> <p>Predictions: </p> <olist> <item> = very significantly impaired; </item> <item> = significantly impaired; </item> <item> = roughly equivalent; </item> <item> = significantly better. </item> </olist> <p>Outcomes: </p> <ulist> <item>5 = significant difference correctly predicted; </item> <item>6 = no significant difference correctly predicted; </item> <item>7 = no significant difference predicted, significant difference obtained, or vice versa; </item> <item>8 = significant difference predicted, significant difference in opposite direction obtained. </item> <item>9 = prediction and outcome match. </item> </ulist> <p>GRAPH: FIGURE 1. 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Dallas, TX: Author. </p> <p>Yap, R., &amp; van der Leij, A. (1993). Word-processing in dyslexics--an automatic decoding deficit. Reading and Writing, 5, 261-279. </p> <p>Yap, R. L., &amp; van der Leij, A. (1994). Testing the automatization deficit hypothesis of dyslexia via a dual-task paradigm. Journal of Learning Disabilities, 27, 660-665. </p> <hd id="AN0004192409-37">APPENDIX</hd> <hd id="AN0004192409-38">Cerebellar tests used in this study</hd> <hd1 id="AN0004192409-39"> Static tests </hd1> <p> <bold> Postural stability. </bold> Each participant was asked to stand upright, looking straight ahead, arms by their side, and was then blindfolded by the experimenter. The experimenter then stood behind the child and explained that she was going to push him or her gently in the back and that he or she should try to stand still. The experimenter then pushed gently in the small of the child's back with her index finger at a 2 kg pressure (the experimenter calibrated herself prior to the session by practicing pushing at 2 kg on a kitchen scale). Pressure was applied for 1.5 seconds and then released. The degree of sway was assessed and recorded for each trial on a scale of 0 for good performance, 1 for a small movement, and 2 for stepping forward or overbalancing. The test was performed six times, three times with the child's arms at his or her side, followed by three pushes with their arms straight out in front, which is slightly more difficult. A child with signs of cerebellar deficit would be predicted to generate a high score, because he or she would be unable to maintain their postural stability. The maximum score for this test was 12. Postural stability scoring had been checked in a previous study (Fawcett et al., 1996) by videotaping a sample of children and getting independent ratings by trained observers unaware of each participant's group. Interrater reliability varied between .94 and .98. </p> <p> <bold> Arm displacement. </bold> Participants were blindfolded and asked to stand with their feet together with their arms held out in front of their body. The experimenter tapped each hand gently in turn for a series of three taps to each hand. Participants were scored for the amount of movement in the limb, on a 3-point scale from 0 to 2, with 0 for the normal response (arms spring back to their original position), 1 for a slight drop in the arm position, and 2 for a clear drop in the arm position. This generated a maximum score of 12 for the six taps. </p> <p> <bold> Limb shake. </bold> The participant was asked to sit down with his or her elbows resting on the chair arm and hands dangling loosely. The experimenter grasped each hand at the wrist and shook it lightly from side to side. Degree of movement was assessed on a scale from 1 (little movement) to 3 (large, floppy movement). </p> <p> <bold> Muscle tone. </bold> Participants adopted the same sitting position, and this time the experimenter told them that she was going to push gently against the child's muscles, and the child's task would be to try and resist. The experimenter pushed against the resistance of the right and left arm, and finally both arms together. Each response was scored for the ability to resist the experimenter's push, on a scale from 0 to 2, generating a maximum score of 6. </p> <hd1 id="AN0004192409-40"> Dynamic Tests </hd1> <p> <bold> Finger and thumb dexterity. </bold> Participants placed the index finger and thumb of one hand onto the index finger and thumb of the other hand. Keeping the top thumb and finger together, they were shown how to separate the lower finger and thumb, and turn one hand clockwise and the other counterclockwise, so that the finger and thumb touched again. This sequence of movements was repeated and practiced until the participant was able to complete the movement fluently five times. The children were then told to perform the successive opposition ten times, as fast as possible. The score noted was the time taken. </p> <p> <bold> Toe tapping. </bold> In this task, participants were given an initial practice and were then asked to tap their foot as fast as they could onto a tin lid. The sounds were recorded on an Apple Macintosh computer, and the speed of tapping assessed accurately using standard waveform analysis software. The score was the time taken to execute 10 taps. </p> <aug> <p>By Angela J. Fawcett; Roderick I. Nicolson and Fiona Maclagan y Ficarra and Michael Silverman </p> <p></p> <p>Angela J. Fawcett, PhD, is a research fellow at the University of Sheffield. Her interests include theoretical and applied dyslexia research and developmental cognitive neuroscience. Roderick I. Nicolson, PhD, is professor of psychology at the University of Sheffield. His current interests include dyslexia and human learning and development. Fiona Maclagan, BA, is a disability support officer at the University of Birmingham. Her interests include the assessment and support of students with dyslexia. Address: Dr. Angela Fawcett, Dept. of Psychology, University of Sheffield, Sheffield S10 2TP, UK (e-mail: A.Fawcett@shef.ac.uk) </p> </aug> |
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| Items | – Name: Title Label: Title Group: Ti Data: Cerebellar Tests Differentiate between Groups of Poor Readers with and without IQ Discrepancy. – Name: Language Label: Language Group: Lang Data: English – Name: Author Label: Authors Group: Au Data: <searchLink fieldCode="AR" term="%22Fawcett%2C+Angela+J%2E%22">Fawcett, Angela J.</searchLink><br /><searchLink fieldCode="AR" term="%22Nicolson%2C+Roderick+I%2E%22">Nicolson, Roderick I.</searchLink><br /><searchLink fieldCode="AR" term="%22Maclagan%2C+Fiona%22">Maclagan, Fiona</searchLink> – Name: TitleSource Label: Source Group: Src Data: <searchLink fieldCode="SO" term="%22Journal+of+Learning+Disabilities%22"><i>Journal of Learning Disabilities</i></searchLink>. Mar-Apr 2001 34(2):119-135. – Name: PeerReviewed Label: Peer Reviewed Group: SrcInfo Data: Y – Name: Pages Label: Page Count Group: Src Data: 17 – Name: DatePubCY Label: Publication Date Group: Date Data: 2001 – Name: TypeDocument Label: Document Type Group: TypDoc Data: Journal Articles<br />Reports - Research – Name: Subject Label: Descriptors Group: Su Data: <searchLink fieldCode="DE" term="%22Dyslexia%22">Dyslexia</searchLink><br /><searchLink fieldCode="DE" term="%22Elementary+Secondary+Education%22">Elementary Secondary Education</searchLink><br /><searchLink fieldCode="DE" term="%22Intelligence+Quotient%22">Intelligence Quotient</searchLink><br /><searchLink fieldCode="DE" term="%22Learning+Disabilities%22">Learning Disabilities</searchLink><br /><searchLink fieldCode="DE" term="%22Slow+Learners%22">Slow Learners</searchLink> – Name: ISSN Label: ISSN Group: ISSN Data: 0022-2194 – Name: Abstract Label: Abstract Group: Ab Data: Tests of phonological, speed, motor and cerebellar tasks were given to 36 students with learning disabilities, 29 of whom were classified as non-discrepant (IQ<90) and 7 as discrepant, (IQ at least 90 and dyslexic). On the cerebellar tests of postural stability and muscle tone, the non-discrepant group performed significantly better than the children with dyslexia. (Contains references.) (Author/DB) – Name: DateEntry Label: Entry Date Group: Date Data: 2001 – Name: AN Label: Accession Number Group: ID Data: EJ623212 |
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| RecordInfo | BibRecord: BibEntity: Languages: – Text: English PhysicalDescription: Pagination: PageCount: 17 StartPage: 119 Subjects: – SubjectFull: Dyslexia Type: general – SubjectFull: Elementary Secondary Education Type: general – SubjectFull: Intelligence Quotient Type: general – SubjectFull: Learning Disabilities Type: general – SubjectFull: Slow Learners Type: general Titles: – TitleFull: Cerebellar Tests Differentiate between Groups of Poor Readers with and without IQ Discrepancy. Type: main BibRelationships: HasContributorRelationships: – PersonEntity: Name: NameFull: Fawcett, Angela J. – PersonEntity: Name: NameFull: Nicolson, Roderick I. – PersonEntity: Name: NameFull: Maclagan, Fiona IsPartOfRelationships: – BibEntity: Dates: – D: 01 M: 01 Type: published Y: 2001 Identifiers: – Type: issn-print Value: 0022-2194 Numbering: – Type: volume Value: 34 – Type: issue Value: 2 Titles: – TitleFull: Journal of Learning Disabilities Type: main |
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