What is the importance and value of research on idiom comprehension in schizophrenia?

To the Editor

Idioms are traditionally defined as a type of expression for which the intended meaning is not derived from the meaning of its individual words; they are part of the wider group of pragmatic language functions for which figurative versus literal interpretations compete. Understanding their comprehension is important because they occur frequently in conversational speech and the media, and because they convey the conventional wisdom, social norms and rules characterising a society. Uunderstanding how people deal with idioms should therefore be a crucial part of any theory of language processing.

Most people use idioms with no apparent difficulty; however, idioms and other figurative language functions are impaired in people with schizophrenia (Mitchell and Crow, 2005). Indeed, a main feature of schizophrenic thought and language disturbance is the inability to understand figurative meaning, also known as concretism. Normally, the contextual constraints in communications bias listeners towards figurative interpretations of idioms. However, patients with schizophrenia often opt for the literal interpretation (Iakimova et al., 2006). It is as if people with schizophrenia seem to expect the literal meaning of ambiguous idioms, unless they are almost invariably used in a figurative manner (Schettino et al., 2010). The importance of deficient idiom comprehension in schizophrenia is underscored by demonstrations that this impairment correlates with cardinal symptoms of schizophrenia such as thought disorder (Iakimova et al., 2010) and the negative symptoms that impact so harshly on social functioning (Schettino et al., 2010). Identifying a specific deficit and understanding its relationship to clinical symptoms could lead to potential avenues of treatment for these impairments of social cognition. Indeed, the study of social cognition may provide insights into the development and persistence of functional disability in schizophrenia, since social cognition seems to act as a mediator between neurocognition and real-world functioning.

At the theoretical level, models of language comprehension in which meaning is derived from compositional analyses of linguistic inputs cannot account for idiom comprehension. Consequently, special models of idiom comprehension in schizophrenia need to be developed to explain the way these common expressions are understood by people with this diagnosis. At present, the mechanisms responsible for the language comprehension failures in idiom comprehension observed in schizophrenia are poorly understood. Older viewpoints conceived impaired idiom comprehension in schizophrenia as representing an inability to construct and maintain an internal representation of context. However, more recent theorising has suggested the close correlation of idiom comprehension with executive dysfunction in schizophrenia (Schettino et al., 2010), which might indicate that it is caused by an inability to inhibit the irrelevant dominant meaning (Titone et al., 2002). Further research is therefore needed as to why idiom comprehension in schizophrenia breaks down, and at what level of processing. Given the link to executive dysfunction, the influence of the dorsolateral prefrontal cortex cognitive control system would seem a particularly promising place to start looking.