Backward masking in schizophrenia and mania. I. Specifying a mechanism.

BACKGROUND: Backward masking is a neuropsychological procedure that involves the earliest phases of visual processing. Compared with normal controls, the performance of schizophrenic patients is more disrupted by a visual mask. Masking procedures used previously with schizophrenic patients have combined two separate masking mechanisms (interruption and integration), which prevent interpretation of the nature of the abnormality. The current study systematically limited the masking mechanism to interruption to specify the underlying mechanisms. Manic patients were included to examine diagnostic specificity.
METHODS: Sixty-three schizophrenic inpatients, 31 manic inpatients, and 48 normal controls received three versions of the backward masking procedure. One version used a high-energy mask that combines both integration and interruption mechanisms. Another procedure used a low-energy mask that works mainly through interruption. A final condition altered the features of the mask so that masking was almost entirely through interruption.
RESULTS: Schizophrenic patients showed performance deficits across masking conditions, even in procedures that were largely limited to masking by interruption. The masking performance of the patients did not appear to fit a simple generalized deficit. Manic patients performed significantly worse than normal controls and comparably with the schizophrenic patients.
CONCLUSIONS: Schizophrenic patients have abnormalities at least with interruptive mechanisms. The results suggest that deficits on masking procedures are not entirely specific to schizophrenia because comparable masking deficits were found in manic inpatients with chronic disease. The current study addresses the neuropsychological mechanisms of the masking deficit. The next step will be to investigate the contributions of two distinct neuroanatomical visual pathways to the masking abnormality in schizophrenia.