Semantic priming in schizophrenia: systematic review and meta-analysis.

BACKGROUND Increased semantic priming is an influential theory of thought disorder in schizophrenia. However, studies to date have had conflicting findings. AIMS To investigate semantic memory in patients with schizophrenia with and without thought disorder. METHOD Data were pooled from 36 studies comparing patients with schizophrenia and normal controls in semantic priming tasks. Data from 18 studies comparing patients with thought disorder with normal controls, and 13 studies comparing patients with and without thought disorder were also pooled. RESULTS There was no support for altered semantic priming in schizophrenia as a whole. Increased semantic priming in patients with thought disorder was supported, but this was significant only in comparison with normal controls and not in comparison with patients without thought disorder. Stimulus onset asynchrony (SOA) and general slowing of reaction time moderated the effect size for priming in patients with thought disorder. CONCLUSIONS Meta-analysis provides qualified support for increased semantic priming as a psychological abnormality underlying thought disorder. However, the possibility that the effect is an artefact of general slowing of reaction time in schizophrenia has not been excluded.