P3a/b. Grand average ERPs to targets in the oddball task, and complex environmental sounds in the novelty oddball paradigm. HC, healthy controls; CHR, clinical high risk; FESZ, first episode schizophrenia patients. Topographical maps indicate scalp distribution of P3a/b in the 3 groups. P3b and P3bn were measured between 315 and 390 ms; P3a between 215 and 285 ms. P3b and P3bn amplitudes measured at Cz and Pz were not different in CHR and FESZ, and both were significantly lower than in HC; P3a amplitude measured at Fz and Cz was also not different in CHR and FESZ but significantly lower than in HC.