Otoacoustic emissions in human ears: normative findings.

Otoacoustic emissions can be separated into two interrelated classes according to the type of eliciting stimulus. On the basis of this categorization, four discrete subtypes can be recognized that include spontaneous, transiently evoked, stimulus-frequency, and distortion-product otoacoustic emissions. Methods of recording and findings in the ears of normally hearing humans are reviewed for each emission type.