Distortion product otoacoustic emission (2f1-f2) suppression in 3-month-old infants:: Evidence for postnatal maturation, of human cochlear function?

The complete timeline for maturation of human cochlear function has not been defined. Distortion product otoacoustic emission (DPOAE)-based measures of cochlear function show non-adult-like responses from premature and term-born neonates at high f2 frequencies; however, older infants were not included in these studies. In the present experiment, previously collected DPOAE ipsilateral suppression data from premature neonates were combined with new data collected from adults, term-born neonates, and 3-month-old infants to further examine the time course for maturation of cochlear function. DPOAE suppression tuning curves (STC) and suppression growth patterns were measured in the three age groups at f2 = 6000 Hz, L1=65, L2=55 dB; SPL, with an f2/f1 of 1.2. Results indicate that term-born neonates and 3-month-old infants have non-adult-like STC width, slope on the low-frequency flank, and tip features. However, the two infant groups are not significantly different from one another. Suppression growth patterns for low-frequency suppressor tones show a clear developmental progression. In general, the younger the infant, the more shallow and compressive the suppression growth for the lowest suppressor frequencies. These findings suggest a high-frequency postnatal immaturity in cochlear function as measured by DPOAE suppression. Results may have been influenced by noncochlear factors, such as middle-ear immaturity. These factors are reviewed and considered. (C) 2004 Acoustical Society of America.