All six sites used the identical experimental paradigm and electrophysiological software and hardware. An internal consistency study by Kuperman et al. (1995) showed that the data from all six laboratory locations were consistent with each other for this paradigm. Subjects were seated on a comfortable chair in a sound-attenuated temperature-regulated and dimly lit booth (Industrial Acoustics Company; Bronx, NY). An Electro-Cap (Electro-Cap International Inc.; Eaton, OH) with 19 leads based on the International 10–20 system (Jasper, 1958) was placed on the scalp of each subject. A forehead electrode served as the ground and the nose electrode served as the common reference. Electrode impedance was maintained below 5 kΩ. For eye movement artifact correction, both vertical and horizontal electro-ocular (EOG) activities were recorded with the electrodes placed supraorbitally and at the outer canthus of the left eye. Amplifier gain was set at 10,000 times on Sensorium EPA-2 Electrophysiology amplifiers (Charlotte, VT), with a high pass filter of 0.02 Hz and low pass filter of 50 Hz and digitized on a Concurrent 5550 computer (Concurrent Computer Corp. Atlanta, GA). The sampling rate
