Attention and masking in schizophrenia

Patients with schizophrenia are known to be impaired in masking tasks, but the mechanisms underlying their deficits are still elusive. Our study was intended to examine attentional effects, which have a known impact on masking in healthy volunteers but have only rarely been explored in relation to masking in patients.

We compared focused versus divided attention in 18 control subjects and 18 patients using forward and backward masking tasks. In the conventional masking task, subjects had to locate one target among four possible locations. Presentation of one target allows attention to be focused, in contrast with the divided attention task in which two targets were presented either in the same hemifield or different hemifields.

Our results reproduce patients' deficits in forward and backward masking tasks but only when one target is presented. We show that control subjects benefit from focused attention, much more so than patients. Furthermore, patients' performance is identical to that of control subjects in backward masking when targets are presented across hemifields. This performance equalization was checked to ensure it was not due solely to the redundancy of signals (two vs. one). We achieved this by comparing performance when two targets were presented in the same vs. across hemifields, the latter yielding a greater redundancy gain.

From the results, it is unlikely that redundancy can account for the whole pattern of results, which suggest instead that attention deficits play a role in backward masking impairments in patients.