Abstract
Forty-two children of at least normal nonverbal intelligence and with a diagnosis of “delayed speech” were subdivided into those having “moderate” and those having “severe” speech difficulties on the basis of the Illinois Test of Psycholinguistic Abilities. Parents of children with “severe” speech difficulties were of much higher social class, and the children were much more likely to have been exposed to potentially traumatic environmental influences than the “moderately” affected children. The “severely” affected probands were also much less likely than the “moderately” affected probands to have relatives with speech disturbances. These data indicate the heterogeneity of the diagnosis of “delayed speech” and suggest parallels to findings in the area of mental retardation, namely, that moderate deficiencies represent the lower end of the normal curve distribution from either a genetic or an environmental perspective, while severe deficiencies are the result of single genes or of serious environmental traumas.
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Byrne, B.M., Willerman, L. & Ashmore, L.L. Severe and moderate language impairment: Evidence for distinctive etiologies. Behav Genet 4, 331–345 (1974). https://doi.org/10.1007/BF01066154
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DOI: https://doi.org/10.1007/BF01066154