Are masking abnormalities in schizophrenia limited to backward masking?

Schizophrenia, it has been proposed, is associated with deficits in the magnocellular part of the visual system. In support of this suggestion, it has been claimed that schizophrenic subjects have abnormal backward masking. However, if this abnormality is to be linked specifically to magnocellular defects, then it must be specific to backward masking, and not, also effect, for example, forward masking. We examined this issue by reviewing the studies of masking in schizophrenic subjects. We find: (i) Most studies (56 out of 67) of backward masking have researched only backward masking. This makes it impossible to determine if the abnormalities found in these studies are exclusively confined to backward masking. (ii) Of those studies (11) that have included both forward and backward masking conditions, the majority found some degree of abnormality under both forward and backward masking conditions. It is concluded that the evidence for linking the abnormalities found in those with schizophrenia specifically to backward masking, rather than masking in general, or more general visual impairments, is at present relatively weak. Given the rationale for using backward masking as a test of magnocellular sensitivity, research in this area does not point to a deficit specific to the magnocellular system.