Figure 4 :The grand average of all trials in which a 60- or 80-dB stimulus did not elicit (left portion) or did elicit (right portion) a K-Complex. When the stimulus did not elicit a K-Complex, a negativity peaking at 350 ms (N350) was visible. It is maximum over central areas of the scalp. Its amplitude was larger following presentation of the 80 than the 60 dB stimulus. When a K-Complex was elicited, a very large negativity was apparent at 550 ms, the N550 (note that the scale is one-fourth that of the left portion). The N550 is maximum over fronto-central areas of the scalp. Although the 80 dB stimulus elicited more K-Complexes than the 60 dB stimulus, the amplitude of the N550 was unaffected by the intensity if the stimulus.