Subjects listened to a random series of infrequent (n=45, 10%) high tones (1000 Hz), infrequent novel sounds (n=45, 10%), and frequent (n=360, 80%) low tones (500 Hz). Subjects were asked to press a response key to each occurrence of the infrequent, high tone (i.e., target stimulus). Transient GBRs were assessed from the frequent tones exclusively. These tones were 80 dB SPL and 50 ms in duration presented with a stimulus-onset asynchrony of 1.25 sec. Sounds were delivered via Etymotic ER-3A insert earphones at 80dB SPL through a STIM audio box (Compumedics Neuroscan).
