Theory of forward and reverse middle-ear transmission applied to otoacoustic emissions in infant and adult ears.
The purpose of this study is to understand why otoacoustic emission (OAE) levels are higher in normal-hearing human infants relative to adults. In a previous study, distortion product (DP) OAE input/output (I/O) functions were shown to differ at f2 = 6 kHz in adults compared to infants through 6 months of age. These DPOAE I/0 functions were used to noninvasively assess immaturities in forward/reverse transmission through the ear canal and middle ear [Abdala, C., and Keefe, D. H., (2006). J. Acoust Soc. Am. 120, 3832-3842]. In the present study, ear-canal reflectance and DPOAEs measured in the same ears were analyzed using a scattering-matrix model of forward and reverse transmission in the ear canal, middle ear, and cochlea. Reflectance measurements were sensitive to frequency-dependent effects of ear-canal and middle-ear transmission that differed across OAE type and subject age. Results indicated that DPOAE levels were larger in infants mainly because the reverse middle-ear transmittance level varied with ear-canal area, which differed by more than a factor of 7 between term infants and adults. The forward middle-ear transmittance level was -16 dB less in infants, so that the conductive efficiency was poorer in infants than adults.
Keefe
Douglas H
DH
Boys Town National Research Hospital, 555 North 30th Street, Omaha, Nebraska 68131, USA. keefe@boystown.org
Abdala
Carolina
C
D000328:Adult; D000375:Aging / Q000502:physiology*; D003051:Cochlea / Q000502:physiology; D004424:Ear Canal / Q000502:physiology; D004432:Ear, Middle / Q000502:physiology*; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D007234:Infant, Premature; D008297:Male; D008962:Models, Theoretical; D017084:Otoacoustic Emissions, Spontaneous / Q000502:physiology*; D011601:Psychophysics; D012016:Reference Values; D013018:Sound Spectrography; D014432:Tympanic Membrane / Q000502:physiology