A study of theory of mind in a group of schizophrenic patients using a mental verb extension task.

An individual has a theory of mind (ToM) if he imputes mental states to himself and others and applies this system to make predictions about the behaviours of others. Findings of cognitive impairment could help us to understand faulty processing mechanisms in schizophrenia. The proposition is that individuals with schizophrenia may be unable to internalize adequately the points of view of others. We tested 27 schizophrenic patients (ICD; WHO). The positive and negative symptom scale (PANSS) was used to assess psychopathology, and the three ToM tasks--first- and second-order false belief tasks and the mental verb extension task--were administered to each subject. Patients who perform well on the ToM first and second order stories do not show problems in the verb extension task. However, the mistakes made in the first and second order stories are also reflected in the verb extension task. The group having difficulties with the first-order story presented more problems in the mental verbs task than the group showing difficulties with the second-order story. This leads us to conclude that the impairments found on the first-order false belief task are more severe and profound than those on the second-order task, and such specific deficits are also seen in the organization of verbs of knowing. It would seem that some schizophrenic patients do not impute mental states to themselves and others, and therefore use the mental verbs wrongly.