Neural response to the second stimulus associated with poor speed discrimination performance in schizophrenia

Visual motion processing is compromised in schizophrenia (SZ), but it is uncertain what neural deviations account for their motion analysis abnormalities. Neural activations were measured with dense-array electroencephalography while 14 medicated SZ and 14 healthy persons performed a paired-stimuli forced choice speed discrimination task. SZ had (a) worse-at-speed discrimination, replicating previous findings, (b) normal early extrastriate neural activity (N1) to both motion stimuli, (c) reduced later extrastriate activity (P2) specifically to the second stimulus, and (d) following P2, an enhanced later N2 over parietal cortex. Stronger P2 and N2 responses were associated with better speed discrimination performance across groups. These findings indicate that the neural correlates of poor motion analysis in SZ may not be an early visual analysis abnormality but a problem with efficient use of speed information later in cognitive processing.