Confusion between silent and overt reading in schizophrenia

The present study was aimed at investigating whether schizophrenic patients are impaired in monitoring their own speech. In particular, we attempted to assess their ability to discriminate between overt and covert speech in a reading task, in order to verify whether they can correctly recollect the modality in which an internally generated action is produced. Subjects were asked to read either silently or aloud, items from a list of words. After a delay of 5 min, they were required to indicate in a new list which words had been read previously (either silently or overtly), or had never been presented during the reading task. With respect to normal controls, schizophrenic patients showed a significant bias to report that they had read aloud words which they had actually read silently, or which were absent during the reading task. The results are discussed in relation to recent neuroimaging studies on inner and overt speech in hallucinating schizophrenic patients. Our data favour the hypothesis that the inability to correctly discriminate between inner and overt speech may play a role in the onset of schizophrenic hallucinations.