Our ERP paradigms were modified from Knight (1984, 1996) and Knight et al. (1989). Subjects were binaurally presented with a quasi-random sequence of 1,000-Hz standard (p = 0.68) and 1,500-Hz target tones (p = 0.16), and physically complex unique novel sounds (p = 0.16), 60 dB over the subjective hearing threshold at a 1.2-second interstimulus interval (NeuroStim; Neurosoft Inc., Charlotte, NC). The duration of standard and target tones was 40 milliseconds (10 milliseconds rise/fall time) and that of the novel sounds 75 to 358 milliseconds. The sequence included 600 sounds and was divided into 3 blocks of 200 sounds each. Subjects were instructed to press a button upon hearing a target, but not to respond to standards or novel sounds. The mean duration of recordings including instructions was 20 minutes. The main experiment was preceded by a training session, consisting of 50 target tones, for which subjects were instructed to press a button every time upon hearing a target.
