Dichotic listening and hemispheric asymmetry in monozygotic twins discordant for schizophrenia
To investigate the effect of schizophrenia on perceptual asymmetry for speech perception, dichotic listening tests were administered to a group of monozygotic (identical) twins discordant for schizophrenia (i.e., one proband has schizophrenia and one does not), and to two concordant control groups where either both members of the twin pair were normal or both had schizophrenia. On the basis of a left hemisphere impairment model of schizophrenia, it was predicted that twins with schizophrenia would show less of a right ear advantage (REA) than normal twins on the dichotic words. Data from both discordant and concordant twin pairs did not support this prediction. Results generally indicated that, like normal twins, most twins with schizophrenia had a REA, and the magnitude of their REA was not significantly different than control values. These results are most consistent with a bilateral hemispheric impairment model of schizophrenia. When the emotional characteristics of the dichotic words (i.e., neutral versus emotionally charged), were examined, it was found that emotional words caused both normal and schizophrenic twins to produce more errors. Finally, there was a tendency for REAs to be larger for men and for right handed subjects across diagnosis.