Electrophysiological recordings were collected as previously described (Ehlers et al., 1999). In brief, a three-tone auditory ‘oddball’ paradigm originally developed to directly model studies employed in humans was used (Ehlers and Chaplin, 1992; Ehlers et al., 1991, 1994). The auditory ERP session consisted of 312 individual tone presentations. Three tone types were presented: standard tones (1000 Hz square wave, 70 dB, 84% probability), rare tones (2000 Hz square wave, 85 dB, 10% probability), and noise tones (white noise, 100 dB, 6% probability). Individual trials were 1000 ms in duration (100 ms pre-stimulus + 900 ms post-stimulus) and were separated by variable intervals ranging from 500 to 1000 ms. Rare tones were interspersed with standards such that no two rare tones occurred successively. The noise tone occurred every 16th trial. Further details about the auditory ERP sessions were described previously (Ehlers et al., 1999).
