In 1981, Galambos and colleagues reported on the "40 Hz auditory potential" which is a continuous 400 Hz tone sinusoidally 'amplitude modulated' at 40 Hz and at 70 dB SPL. This produced a very frequency specific response, but the response was very susceptible to state of arousal. In 1991, Cohen and colleagues learned that by presenting at a higher rate of stimulation than 40 Hz (>70 Hz), the response was smaller but less affected by sleep. In 1994, Rickards and colleagues showed that it was possible to obtain responses in newborns. In 1995, Lins and Picton found that simultaneous stimuli presented at rates in the 80 to 100 Hz range made it possible to obtain auditory thresholds.