Figure 7 :The processing of a stimulus that slowly decreases in intensity from 70 to 0 dB SPL (left portion) or slowly increases in intensity from 0 to 70 dB (right portion). Subjects were asked to attend to the auditory stimuli or to ignore them and read a book. The ERPs represent the grand average of four subjects. A large N1 (closed arrow) and a P2 were elicited by the initial onset of the slowly decaying stimulus whether attended or ignored. Attention did affect a later waking N2 (open arrow). The gradual decline in the intensity of the stimulus was associated with a decline in the amplitude of the SP. When the stimulus slowly increased in intensity, a smaller amplitude N1 and waking N2 remained visible in spite of its low initial intensity. The SP was present during the entire duration of the stimulus. Attention might also affect the N2 elicited by the abrupt offset of the now obtrusive stimulus.