Cochlear traveling-wave delays estimated by distortion-product emissions in normal hearing adults and term-born...

Functional aspects of human cochlear maturation were studied with distortion-product otoacoustic emissions (DPE). Cochlear travel times were measured on basis of the phase-frequency relationship for DPEs in 54 term-born babies (36 to 42 weeks conceptional age [CA]) for f2 frequencies from 1.7 to 10 kHz, and the results were compared with a normaltive data set based on 36 adult ears. At the two extremes of the f2 frequency range used, 1.7 kHz and 2.4 kHz on the low end and 7 kHz and 10 kHz on the high end, the travel times for neonates were similar to those in adult ears. In the mid-frequency range (3.4 kHz and 4.8 kHz) the mean values were significantly smaller than those for adults. We attempt to explain these findings on the basis of the maturation of two partially compensating (i.e., with cochlear travel time) cochlear mechanisms: the maturation of the characteristic frequency (CF)-place relationship in the cochlea (the "shifting place" principle) and the maturation of the cochlear amplifier.