Figure 3 :Grand-averaged ERPs following presentation of an 80 dB tone during stage 2 sleep. Note the difference in the amplitude and time calibration scales compared with previous figures. A long 8 s sweep time is displayed to incorporate the responses to all five stimuli within the train. The upper portion of the figure displays the grand average of all trials in which a K-Complex was not elicited. A large amplitude (approximately 25 ýV) negative wave peaking at about 350 ms (N350) is apparent following presentation of the initial stimulus. On approximately 35% of trains, a large amplitude K-Complex was elicited by the initial stimulus in the train (lower portion of the figure). Its amplitude exceeded 100 ýV. The ERPs to the remaining four stimuli in the train are difficult to discern in the large amplitude background EEG of NREM sleep. Adapted from Campbell et al.