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Patterns of psycholinguistic development in the severely mentally retarded: a hypothesis.

Abstract We hypothesize that the loss of psycholinguistic skills in some cases of severe mental retardation caused by prenatal disruption closely approximates ontogenetic patterns of language acquisition and phylogenetic patterns of cognitive development. This hypothesis was tested on 131 trainable mental retardates divided into four etiological classes. The results support the hypothesis and show that certain patterns of loss occur only in mental retardation resulting from prenatal disruption and characterized by postnatal developmental delay and do not occur in postnatal environmentally caused retardation.