[Visual backward masking in schizophrenia].

Visual backward masking is used to investigate the function of attention as the initial stage of visual information processing by measuring the shortest stimulus presentation time for accurate cognition. This is achieved by applying a masking stimulus after target stimulus presentation. In this study, 50 controls and 50 schizophrenics (paranoid type) were examined by this method. In the control group, 1) there was a significant decline in correct answers to the target stimulus with age; and 2) there was a significant increase in correct answers with repetition. However, in the schizophrenic group, 1) there was a significantly lower number of correct answers in all age groups compared to that in the controls, along with a greater decline in correct answers with age; and 2) there was no increase in correct answers with repetition; 3) good performers among the schizophrenic patients were young with a short duration of illness and on a low dose of medication. Poor performers showed numerous positive and negative psychotic symptoms, were not on medication, or had positive findings on CTscan; furthermore, 4) longitudinal re-examination of the same subjects showed that even when psychotic symptoms improved and the subjects were able to return to society, their ability to give correct answers remained significantly different compared to that of the controls. These findings seem to reflect the trait-dependence aspect of schizophrenia (paranoid type) on a visual backward masking task. Furthermore, visual backward masking seems to be a convenient and useful measure for this aspect of attention and its trait-dependence in schizophrenia.