DISTORTION-PRODUCT OTOACOUSTIC EMISSIONS IN HUMAN NEWBORNS AND ADULTS- II - LEVEL EFFECTS

This study varied the levels of the primaries and recorded distortion product otoacoustic emissions (DPOAEs) from human newborns and adults. Preterm as well as term newborns were tested. The 2f(1)-f(2) DPOAE wa s the most reliably recorded DPOAE, especially at low levels of the pr imaries. Amplitude and phase reproducibility deteriorated with decreas ing level of the primaries. Newborn DPOAEs were slightly less reproduc ible than adult DPOAEs. The underlying DPOAE I/O functions were nonmon otonic for both newborns and adults. Unity gain characterized the init ial increasing portion of those functions in most subjects. Although n ewborn and adult I/O functions were similar, they did differ. In parti cular, adult functions tended to be more linear with saturation at hig her primary levels. Some of the newborn functions saturated at very lo w stimulus levels. Although differences in cochlear mechanics may expl ain developmental difference in DPOAE I/O functions, developmental dif ferences in the resonance characteristics of the outer and middle ears may also be involved. (C) 1998 Acoustical Society of America. [S0001- 4966(98)02702-7].