Paracontrast and metacontrast in schizophrenia: clarifying the mechanism for visual masking deficits.

Schizophrenic patients consistently demonstrate performance deficits on visual masking procedures. Visual masking can occur through two distinctly different mechanisms: interruption and integration. One highly effective way to limit the masking mechanism to interruption is to use a mask that surrounds, but does not spatially overlap, the target. These procedures are called paracontrast and metacontrast (for forward and backward masking, respectively). Despite their clear advantages for interpretation, paracontrast and metacontrast have not been used previously in schizophrenia. In the present study, we examined the reliability of the paracontrast and metacontrast procedures by administering these tasks to 103 schizophrenic patients and 49 normal control subjects. In addition, we compared the results to those from a low-energy masking condition, which is an alternative way to limit masking to interruption. Patients showed deficits on both the paracontrast and metacontrast procedures. The deficits in paracontrast and metacontrast were comparable to those seen previously with low-energy masking. These results suggest that the paracontrast/metacontrast procedure and the procedure using a low-energy mask are roughly equally sensitive to deficits in early visual processing among schizophrenic patients. These results bolster previous conclusions that schizophrenic patients show deficits on visual masking tasks even when masking on those tasks occurs entirely through the interruption mechanism.