Separate ERPs for nontarget, target and novel stimuli were averaged from artifact-free trials. The means for the number of trials (±SD) used to compute these ERP averages were 250.1 ±31.7, 38.8 ±5.6 and 34.9 ±6.3 (nontarget, target and novel, respectively) for CHR patients, and 265.1 ±16.6, 39.3 ±2.6 and 36.6 ±4.7 for healthy controls (no fewer than 20 trials per ERP), and there were no significant differences between patients and controls, F(1, 38) = 2.55, p = .12. Furthermore, a satisfactory signal-to-noise ratio for each condition was confirmed by visual inspections of the individual ERP waveforms of each participant. ERP waveforms were screened for electrolyte bridges (Tenke & Kayser, 2001)1, low-pass filtered at 12.5 Hz (−12 dB/octave), and baseline-corrected using the 100 ms preceding stimulus onset.
