Auditory Hallucinations and Reduced Language Lateralization in Schizophrenia: A Meta-analysis of Dichotic Listening Studies

Reduced left-hemispheric language lateralization has been proposed to be a trait marker for schizophrenia, but the empirical evidence is ambiguous. Recent studies suggest that auditory hallucinations are critical for whether a patient shows reduced language lateralization. Therefore, the aim of the study was to statistically integrate studies investigating language lateralization in schizophrenia patients using dichotic listening. To this end, two meta-analyses were conducted, one comparing schizophrenia patients with healthy controls (n=1407), the other comparing schizophrenia patients experiencing auditory hallucinations with non-hallucinating controls (n=407). Schizophrenia patients showed weaker language lateralization than healthy controls but the effect size was small (g= -0.26). When patients with auditory hallucinations were compared to non-hallucinating controls, the effect size was substantially larger (g= -0.45). These effect sizes suggest that reduced language lateralization is a weak trait marker for schizophrenia as such and a strong trait marker for the experience of auditory hallucinations within the schizophrenia population. (JINS, 2013, 19, 410-418)