Speech disorder in schizophrenia: review of the literature and exploration of its relation to the uniquely human capacity for language

The language capacity of modern humans is thought by some to be clearly distinct from that of nonhuman primates (Bickerton 1990). Crow (1997, 1998a) has proposed that a disturbance in the uniquely human aspects of language is central to the genetic etiology of schizophrenia. A review of the literature on language disorder in schizophrenia provides evidence for widespread deficits in comprehension, production, attention, and cerebral lateralization of language. We focused here on those anomalies that are uniquely human aspects of language. Bickerton's five distinctly human language devices were examined in patients with schizophrenia and their families by using a structured scoring format on oral soliloquies. The chronic patients showed reduced use of clausal embedding and used fewer words than first episode patients or well family members. The amount of sentence complexity was found to be familial and to cosegregate with schizophrenia within families. These data are consistent with previous literature and additionally show a familial component to these measures, thus suggesting that deficits in specifically human aspects of language may be related to the genetics of schizophrenia.