The development of morphology and syntax in a pair of DZ twin boys

Twins provide a natural set-up for the study of some of the basic issues that concern the field of language acquisition and of developmental language disorders and brain pathology, in that they present a unique hereditary and environmental situation within which development takes place. Yet, few studies have detailed the development of formal aspects of language in twins. This paper reports on a prospective, longitudinal study of the acquisition of selected aspects of Hebrew syntax and morphology in a pair of DZ twin boys, aged 3;6-4;0, one of whom had a congenital brain abnormality. MLU levels suggest a marked delay for both children in the onset and progression of language development. However, both the healthy and the brain-injured twin followed a normal developmental course. Data to that effect concern frequency of sentences of various lengths, distribution of sentence types, use of tenses, use of pronouns, correct usage of various syntactic markers, variability of verb types and tokens and the distribution of errors of morphology and morphophonology. It is argued that this case study offers support for claims concerning brain plasticity for language. Furthermore, it is in line with previous studies of normal and brain-injured children which, rather unexpectedly, pointed at the relative ease with which formal, linguistic systems were acquired.