During the 1990's an alternative to ECOG and ABR was developed to estimate hearing threshold from AEPS, the auditory study - state responses technique.  The ASSR is similar to CAP and ABR in that brain potentials to sound are measured.  The stimuli used to evoke ASSRs are pure tones that are amplitude and/or frequency modulated. The ASSR appears to be generated by the same neural structures as the AEP's evoked by transient sounds, but this depends on both modulation rate and subject state.  In sleeping infants and young childrens, pure tones modulated at rates of 60-120 HZ yield reliable responses, and the characteristics of ASSR's at these rates are similar to those for the ABR.

References:  Deaf studies, language, and education.