Figure 2 :The effects of stimulus intensity level on ERPs elicited by slowly-presented stimuli (about every 10 seconds) during the waking and sleeping states. Again, the ERPs elicited during NREM are traced at one-half amplitude relative to wakefulness and REM conditions. In the waking state, a larger and later N1 was elicited compared to when stimuli were presented rapidly. A P3a was elicited for both the 80 dB and lower intensity 60 dB stimuli. Again, N1 was not visible during NREM sleep, and it was attenuated during REM sleep. During REM, a small P3a was apparent but it was not significantly different from the pre-stimulus baseline level. A very large amplitude N350 was elicited in all stages of NREM sleep. A small amplitude N350 was even apparent following presentation of the low intensity 40 dB stimuli.