A longitudinal study of distortion product otoacoustic emission ipsilateral suppression and input/output characteristics in human neonates.

Past work has shown that distortion product otoacoustic emission (DPOAE) (2f1-f2) ipsilateral suppression and input/output (I/O) characteristics are not adult-like in prematurely born neonates [Abdala, J. Acoust. Soc. Am. 110, 1465-1476 (2001)]. These age differences are most pronounced at f2 = 6000 Hz and have been interpreted to indicate a subtle immaturity in human cochlear function prior to term birth. It is still not clear, however, whether term-born neonates are completely adult-like in cochlear function. To study this question, DPOAE suppression and I/O functions for f2 = 6000 Hz were measured in a group of prematurely born neonates at weekly intervals over a period of 7-8-weeks, a group of normal-hearing adults, and during a one-time test session in a group of term-born neonates. Results show that there was no significant change in suppression tuning, suppression growth, and various I/O characteristics across test session for premature neonates, but there was an age-group effect; even once prematurely born neonates reached the equivalence of term-like status (38-40-weeks postconceptional weeks), they continued to show narrower suppression tuning than adults, shallower suppression growth for low-frequency side suppressor tones, and an elevated amplitude saturation plateau on the I/O function. Term-born neonates showed DPOAE results that were comparable to those measured from premature neonates and unlike adult findings. These results suggest that a subtle immaturity in cochlear function persists into the postnatal period.