Abstract
Previous research suggested that the conscious perception of masked stimuli is impaired in schizophrenia, while unconscious bottom-up processing of the same stimuli, as assessed by subliminal priming, can be preserved. Here, we test this postulated dissociation between intact bottom-up and impaired top-down processing and evaluate its brain mechanisms using high-density recordings of event-related-potentials. Sixteen patients with schizophrenia and sixteen normal controls were exposed to peripheral digits at various degrees of masking, under conditions of either focused attention or distraction by another task. In the distraction condition, the brain activity evoked by masked digits was drastically reduced in both groups, but early bottom-up visual activation could still be detected and did not differ between patients and controls. By contrast, under focused top-down attention, a major impairment was observed: in patients, contrary to controls, the N1 component was insufficiently amplified by attention, and the late non-linear ignition associated with the P3 component was drastically reduced. Interestingly, the patients showed an essentially normal attentional amplification of the P1 and N2 components. These results suggest that some but not all top-down attentional amplification processes are impaired in schizophrenia, while bottom-up processing seems to be preserved.