Are masking abnormalities in schizophrenia specific to type-B masking?

The abnormal visual masking in those with schizophrenia, it has been proposed, arises from a deficiency in their magnocellular system. Two kinds of masking exist: Type-A and Type-B. Type-A masking is characterized by the masking being strongest when target and mask are presented simultaneously. Type-B masking is characterized by a non-monotonic masking curve, i.e. the masking is largest when the mask is presented at some time after the target. The proposed link between masking and magnocellular activity applies mainly to Type-B masking. Thus, a magnocellular deficiency, if it exists, should effect Type-B masking more prominently than Type-A masking. Here we review the relevant literature. The majority of studies of masking in those with schizophrenia, it is found, have examined only Type-A masking. These find substantial evidence for abnormal masking. Where Type-B masking has been obtained, evidence also exists for abnormalities. However, the abnormal masking in these cases is largely unrelated to the defining characteristic of Type-B masking (i.e. to the non-monotonic masking function). It is concluded that the evidence for linking masking abnormalities in schizophrenia specifically to Type-B masking is weak. This undermines the proposal that masking abnormalities in schizophrenia have a magnocellular origin.