Specific reading disability: Follow-up studies

Twenty-four children with specific reading disability, originally studied and treated at the Bellevue Hospital Mental Hygiene Clinic between 1949 and 1951, were reexamined as young adults between 1961 and 1962 with the battery of tests given to them ten to 12 years before. Their specific perceptual problems and evidence of lack of clear- out cerebral dominance persists, although in less severe form. Those patients who as children had neurological signs in addition to the specific reading disability showed less improvement than those who had none.     

Temporal processing and reading disability

The present investigation examined thehypothesis that early auditory temporalprocessing deficits cause later specificreading disability by impairing phonologicalprocessing (Farmer & Klein 1995; Tallal1980, 1984). Temporal processing ability atschool entry was examined using Tallal'sRepetition Test in a large unselected sample ofover 500 children followed over subsequentyears. Although our data confirmed the presenceof certain non-speech auditory processingdeficits in children later classified asspecific reading-disabled, many findings wereclearly at odds with a causal interpretation ofthis relationship. (1) Reading-disabled (RD)children were impaired at school entry on thesubtest with long interstimulus intervals(ISIs) but not the critical short-ISIsubtest. (2) RD children were not inferior toreading-age (RA) controls. (3) A subgroup of RDchildren with evidence of temporal deficitswere no less proficient on later phonologicalor reading measures than RD children with noevidence of early temporal impairment. (4)Although there was a reliable concurrentcorrelation between temporal deficits andphonological awareness at school entry(suggesting a possible common causeexplanation), early temporal deficits did notpredict later phonological impairment,pseudoword processing difficulties, or specificreading disability. On the other hand, earlytemporal deficits did predict later oralreceptive vocabulary and reading comprehensionweaknesses. These findings suggest thatauditory temporal deficits in dyslexics may beassociated with the same dysphasic-typesymptoms observed by Tallal and her colleaguesin specific language-impaired populations, butdo not cause the core phonological deficitsthat characterize dyslexic groups.     

Identifying sex differences in reading disability

The issue of sex differences in reading disability has been of recent interest in relation to sex ratios in families with reading disabled children and to possible sex biases in referred populations. Data from a study of 570 twins are used to develop alternative definitions of reading disability that vary in the manner to which sex effects are taken into account. These definitions include discrepancies between reading quotients and IQ, the use of the regression of reading onto IQ and chronological age/reading age differences. In each case the reading and spelling disability was defined either separately for the sexes or based upon the data for the sexes combined and with and without an IQ>90 exclusion criterion. The consequences of using the alternative definitions for prevalence, sex ratio and heritability are examined. The results demonstrate that the characteristics of reading disabled children vary with the way disability is defined. The excess of males seems to be a robust finding. Definitions that take into account differences in mean score for males and females reduce but do not eradicate the sex ratio. From the genetic analysis, there is no support for the suggestion that the genetic effect on reading is greater for females than males. It is concluded that the use of regression based procedures for identifying reading disability is desirable but that at present there is insufficient evidence to justify the adoption of separate regression procedures for the two sexes.     

Persistent arithmetic, reading, or arithmetic and reading disability

The achievement of 1,075 school children was followed to the end of grade 7 or 8. Retrospective details of birth, medical history, and infant adaptive behavior, as well as current information about preschool behavior, were provided by parents before kindergarten entry when their children were ages four to five. At that time, each child was given language, preacademic, and visual-motor tests, and a short-form verbal IQ was obtained. For grades 1 to 8, a mean 6.9 percent qualified as low in arithmetic (including 3.9 percent low only in arithmetic) and 9 percent as low in reading (including 6 percent low only in reading). Groups of children with persistent disability in arithmetic only (2.3 percent), reading only (6.6 percent), and arithmetic plus reading (3.4 percent) were compared on all variables, and gender differences were examined. The specific arithmetic group was superior to the other two groups in preschool verbal IQ and language, and had suffered more birth problems and illness. As found by Rourke and his colleagues (e.g., Rourke and Finlayson 1978) for older children, boys with a specific arithmetic disability showed a preschool profile with high verbal scores and low nonverbal scores. Many gender differences were found for the total sample, but few for the learning disability subgroups.     

Diagnostic considerations in children with reading disability

Summary Nine out of ten children with reading disability are found to have a basic syndrome consisting of signs related to lack of clear-cut cerebral dominance. Two of these nine children have additional signs suggestive of structural brain damage. One out of ten children with reading disability does not have any of these findings. The methods of detecting these groups are described and therapeutic implications indicated. The data described in this paper have been previously reported in: SILVER, A. A. and HAGIN, R., “Specific Reading Disability: Delineation of the Syndrome and Relationship to Cerebral Dominance,” COMPREHENSIVE PSYCHIATRY, 1, 2 (April, 1960), pp. 126–134. The author is indebted to Dr. Rosa A. Hagin for permission to use this material. From BULLETIN OF THE ORTON SOCIETY, Vol. XI, 1961, pp. 5–12.     

Colorado longitudinal twin study of reading disability

The primary objectives of the present study are to introduce the Colorado Longitudinal Twin Study of Reading Disability, the first longitudinal twin study in which subjects have been specifically selected for having a history of reading difficulties, and to present some initial assessments of the stability of reading performance and cognitive abilities in this sample. Preliminary examination of the test scores of 124 twins with a history of reading difficulties and 154 twins with no history of reading difficulties indicates that over the 5- to 6-year interval between assessments, cognitive and reading performance are highly stable. As a group, those subjects with a history of reading difficulties had substantial deficits relative to control subjects on all measures at initial assessment, and significant deficits remained at follow-up. The stability noted for all cognitive and achievement measures was highest for a composite measure of reading, whose average stability correlation across groups was 0.80. Results of preliminary behavior genetic analyses for this measure indicated that shared genetic influences accounted for 86% and 49% of the phenotypic correlations between the two assessments for twin pairs with and without reading difficulties, respectively. In addition, genetic correlations reached unity for both groups, suggesting that the same genetic influences are manifested at both time points.     

Cluster analytic classification of reading disability subtypes

Cluster analysis was employed to identify subtypes of reading disability in a sample of 140 reading-disabled children using factor scores obtained from a battery of psychometric tests. Preliminary results suggested the existence of three subtypes, but closer scrutiny of the data indicated that individual differences are more accurately characterized by continuity in the measurement space. This result demonstrates the need for detailed validation of findings from applications of cluster analysis. Despite the absence of homogeneous subtypes, the characterization of individual strengths and weaknesses on psychometric measures may nonetheless be important for diagnosis and remediation in the educational setting.Behavioral Research Institute