The perception of ambiguous words in patients with schizophrenia

Various interactive models have proposed that a number of disorcered cognitive processes observed in schizophrenia could depend on a spesific impairment in the processing of contextual information. That is to say, schizophrenic patients have a degraded ability either to construct and maintain internal representations of the context or to inhibit contextually irrelevant information that hinders the comprehension of the targets meaning. Earlier studies have suggested that deficits in processing contextual information become apparent when patients with schizophrenia use the most common meaning of an ambiguous word or when they ignore the linguistic violations in sentences while they are looking for the target-word. The present study intends to investigate patientsí ability to process ambiguous words (nouns and verbs) by using context dependent information.

19 patients with schizophrenia and 19 controls participated in our study. We administered the BPRS and the TLC scale. Two groups of patients with schizophrenia were formed on the basis of their TLC scores: patients without thought disorder (N=7), TLC score <=7 , and patients with thought disorder (N=12), TLC score >7. Those two groups of patients were matched for age, duration of illness and education level. In addition, we administered an ambiguous words test, in which the participants were presented with a set of 20 sentences (10 with ambiguous nouns and 10 with ambiguous verbs) and were asked to select the meaning of the target word (ambiguous noun or ambiguous verb) among three options, in order to form a meaningful sentence. One of the options had the correct meaning according to the contextual information, the order corresponded to the literal meaning of the target word, which was semantically irrelevant to the context (semantic error) and the third was phonologically similar to the target word (phonological error).

The results showed that patients with schizophrenia, especially those with thought disorder (TD), performed worse than controls on the ambiguous word test. In particular, the subtest of the ambiguous nouns differentiated among the three groups (patients with schizophrenia without TD, patients with schizophrenia with TD and controls), while the subtest of ambiguous verbs differentiated between patients with TD and controls. Additional analysis was performed in order to examine the kind of errors made by the three groups. It appeared that both patients with schizophrenia and controls made the same kind of errors in the test of ambiguous words, viz.more semantic than phonological errors. Both patients and controls made more semantic than phonological errors in the subtest of ambiguous nouns. This pattern was not observed in the subtest of ambiguous verbs, i.e. there was no difference concerning the type of errors. Further analysis has showed that the performance of schizophrenic patients correlated significantly with their age and duration of illness but not with their scores in BPRS.

This study indicates that patients with schizophrenia and especially those with thought disorder (TD) performed poorly on tasks involving context processing. These results are consistent with other studies demostrating schizophrenic patientsí deficit with respect to the use of context information and indicate that patients with TD face more difficulties than those without TD. The latter result emphasizes the cognitive heterogeneity of schizophrenic patients and coincides with recent data reporting severe impairment in patients with TD, concerning the associative memory and the processing of pre-lexical information. Last but not least, these difficulties are more marked in the ambiguous noun subtest, compared to that of ambiguous verbs. While nouns and verbs are regarded as equally important in communication, the structural contextual information for nouns is more abstract; besides, the mmeaning of the nouns is more contextually dependent compared to that of verbs (cp. verb and noun valence).

These findings suggest the need for additional research focusing both on the cognitive and the linguistic aspect of the specific impairment, which will contribute in our understanding of the decreased ability to use contextual information in schizophrenia.

Key words: Schizophrenia, thought disorder, ambiguous words, contextual information.