Normal electrocortical facilitation but abnormal target identification during visual sustained attention in schizophrenia

Attentional deficits in schizophrenia have been investigated using target identification tasks which conflate the abilities to successfully (1) attend to possible target locations and (2) detect target events. Whether compromised attentional selectivity or abnormal target detection causes schizophrenia subjects' poor performance on visual attention tasks, therefore, is unknown. To address this issue, we measured the neural activity (using electroencephalography) of 17 schizophrenia and 17 healthy subjects during a target identification task. Participants viewed superimposed images (horizontal and vertical bars differing in color) and attended to one image to identify bar width changes in specific locations. Bars were frequency tagged so attention directed to unique parts of the images could be tracked. Steady-state visual evoked potentials (ssVEPs) were used to quantify attention-related neural activity to specific parts of the visual images. Behavioral performance and event-related potentials (ERPs) in response to the target events were used to quantify target detection abilities. For both schizophrenia and healthy subjects, attending to specific parts of the attended image enhanced brain activity related to attended bars and reduced activity evoked by unattended bars. Activity in relation to the spatially overlapping unattended image was unaffected. Schizophrenia patients, however, were impaired on target detection abilities on both behavioral and brain activity measures. Target-related behavioral and brain activity measures were highly correlated in both groups. These findings indicate that deficient target detection rather than compromised attentional selectivity accounts for previously reported visual attention deficits in schizophrenia.