Effect of orthography on the verbal fluency performance in schizophrenia: examination using Japanese patients

Abstract 

Letter fluency performance is less impaired than the category fluency performance in alphabetical-language speakers with schizophrenia. The purpose of this study was to determine whether the same pattern in the performance on the two verbal fluency tasks exists in subjects using a non-alphabetical language. In the Japanese orthography, there is one-to-one correspondence between sound (syllable) and graphemes (“kana” script), in contrast to one-to-many associations in alphabetical languages (e.g. English, French). The category fluency task (ANIMAL, FRUIT) and the letter fluency task (“KA”, “TA” in “kana” script) were administered on 38 patients with schizophrenia and the equal number of normal controls. In order to examine the influence of psychotic symptoms on the verbal fluency performance, the Scale for the Assessment of Positive Symptoms (SAPS) and the Scale for the Assessment of Negative Symptoms (SANS) were administered. The patients performed significantly worse both in the letter- and category fluency tasks compared with control subjects. However, performance on the letter fluency task and category fluency task was similarly impaired in Japanese patients with schizophrenia, unlike the results in previous studies with alphabetical-language speakers. On the other hand, Alogia symptoms, as assessed by SANS, was a significant predictive variable in the regression model for the category fluency task score (ANIMAL), whereas the factor of the other domains of negative symptoms as a whole was a significant predictive variable in the model for the letter fluency task score (TA), which confirmed the findings in previous studies with alphabetical-language subjects. These results suggest that the pattern of impairment in the verbal fluency performance in schizophrenia is dependent on the specific language systems used by the patients although the degradation of the verbal fluency performance is influenced by some types of negative symptoms irrespective of the language system.

Keywords:  Schizophrenia, Letter fluency task, Category fluency task, Psychotic symptoms, Negative symptoms, Language system