Visual information decoding deficits in schizophrenia

Abstract

Schizophrenic and control subjects were tested on two-flash fusion (TFF) and visual backward masking (VBM) tasks in a repeated measures design. Each subject was tested in a single session. Both tasks used the same equipment and stimuli. There was no difference between the groups in their ability to detect the presence of two separate stimuli in the TFF task. Schizophrenic subjects did require longer interstimulus intervals (ISI) than control subjects to accurately report one of the two targets in the VBM task. Analysis of individual targets reveals that the VBM deficit is a function of the similarity of the target and mask. The more feature detail discrimination necessary, the longer an ISI is required in VBM. The data are interpreted as supporting the conclusion that since the groups did not differ in their performance of the TFF task, which would also have been affected by a sensory abnormality, the deficit in VBM must be explained by reference to a higher level of information processing. The VBM deficit is a failure to decode the target stimulus, and is not simply a function of abnormalities due to an overactive transient channel system.