ABSTRACT
Mentally retarded children differ in presence and degree of biological deficit as well as in severity of cognitive deficit. Because of this heterogeneity, analyses of total groups of retarded children may obscure some antecedent factors and attribute inappropriate generality to others (Birch et al., 1970). In the present study, a majority of the severely retarded and a small minority of the mildly retarded had major neurological disorders (see Tables 3-5, 3-6, and 3-10). As noted earlier, prevalence of these disorders at both levels of retardation was related to ethnicity and to social class, with the highest proportion of neurologically abnormal children (82%) among the severely retarded whites in the highest SES group (see Table 3-5). To the extent that associated neurological abnormalities explain or account for mental retardation (and this differs in degree, as in Down's syndrome and epilepsy), then children without clear clinical signs of CNS pathology pose the largest etiological questions and are the primary focus of this chapter.
