New results in the experimental psychopathology of visual dysfunctions in schizophrenia

New theories of schizophrenia put a special emphasis on cognitive deficits, including executive functions, attention, verbal memory, and psychomotor speed. Dysfunctions of low level visual processing are less known. In this paper, the author summarizes recent results from two new tasks and integrates them with the relevant literature of schizophrenia. First, the relationship between the precortical magno (M) and parvocellular (P) pathways was investigated with a new contrast categorization task assessing low level perception, memory, and abstraction. Patients with schizophrenia showed a generalized dysfunction, which suggests contrast-independent memory and abstraction problems. In contrast, siblings were selectively impaired on the task variant that included the 10-15% contrast range, the transition zone between M and P pathway contrast sensitivity. In a second paradigm, the author investigated intrinsic lateral connectivity in the primary visual cortex, the main target of M and P pathways. Using Gabor patches, a reduced facilitation effect of collinear flankers was demonstrated in schizophrenia, which suggests impaired lateral connections in the primary visual cortex. These results are closely related to backward masking and smooth pursuit eye movement abnormalities. As a neurobiological basis of these phenomena, N-methyl-D-aspartate (NMDA) glutamate receptors and integrated synaptic networks may be of special relevance.