Domain-specific deficits in schizophrenia

Introduction. Object recognition deficits are well documented in certain neurological disorders (e.g., Alzheimer's disease, herpes simplex encephalitis). Although agnosic problems have been documented in some patients with schizophrenia (Gabrovska et al., 2003), no study has investigated whether such deficits differentially affect specific categories of information (as they sometimes do in neurological cases). Method. In Part I of this study, we compared object recognition in 55 patients with chronic schizophrenia and 22 age- and NART IQ-matched healthy controls. In Part II, we present a detailed case study of one patient with schizophrenia (DH) who displays a severe category specific semantic knowledge for living things. Results. Of the patients with schizophrenia, 75% had object recognition below the 5th percentile, and in 11% of cases, a highly specific classical category dissociation emerged (5 cases with nonliving deficit and 1 with living deficit); and two other patients showed strong dissociation for living things. These findings provide convincing evidence of a classical double dissociation across the two categories. In Part II, the in-depth case study of one schizophrenic patient (DH), documented a profound agnosia for living things. While DH displayed intact low level perceptual and spatial ability and could copy drawings, he was severely impaired at naming, picture-name matching, semantic fluency, and could not describe or draw items from memory. Conclusions. The presence of impaired object recognition in most schizophrenic patients, along with highly selective category specific deficits in a minority, is discussed with reference to similar findings in neurological patients.