Visual information processing in patients with schizophrenia: evidence forthe impairment of central mechanisms

Patients with schizophrenia are especially impaired in the detection of spa tial location if the briefly presented target stimulus is followed by a mas k in a close temporal proximity (target location backward masking (BM) para digm). It has been suggested that this phenomenon is related to the impairm ent of low spatial and high temporal frequency-sensitive transient (magnoce llular) visual channels. To test this hypothesis, we measured target locati on BM and visual contrast sensitivity (CS) in clinically remitted patients with schizophrenia. In the BM task, subjects were asked to indicate the pos ition of letters appearing at four possible spatial locations. In the CS te st, a two-alternative forced choice method was used to measure the minimal contrast level required for the detection of horizontal gratings set at low spatial and high temporal frequencies (0.5 cycle/degree and 8 Hz, respecti vely). We found that the schizophrenia patients with normal CSs (spared tra nsient channel functions) showed a marked deficit in the target location BM task. This suggests that the abnormality of subcortical transient channels does not explain some visual information processing dysfunctions in schizo phrenia. Instead, deficient cortical interactions of rapidly changing envir onmental signals may be involved. (C) 2000 Elsevier Science Ireland Ltd, Al l rights reserved.