Probe-Tube Microphone Measures with Very Young Infants

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Abstract
The feasibility and practicalities of performing probe-tube microphone measures with infants is addressed, as well as two aspects of acoustic functioning of infant ears: the real ear unaided response (REUR) and the real ear to coupler difference (RECD). Part 1 is a longitudinal study involving 12 infants. Serial measures of REUR were obtained over an 18-mo period. Infants were < or = 3 mo for the first test and < or = 21 mo at the last test visit. Practicalities of probe-tube microphone testing of unsedated infants and changes in the position (i.e., frequency) of the primary REUR peak were addressed. For part 2 of the project, 33 infants under 12 mo of age took part. A comparison of real ear hearing aid gain versus coupler gain was made. Test-retest differences for real ear aided response were estimated. Part 1 results indicate that probe-tube microphone measures in unsedated infants are feasible and show good within-subject repeatability. REUR measures for the more alert and mobile older subjects, as for the younger infants, showed an acceptably small degree of intersubject variability. The frequency of the primary REUR peak decreased during the first year of life, with a group mean of 2932 Hz reached at the end of the first year. However, thereafter, instead of stabilizing at around this value there was considerable fluctuation in the frequency of REUR peak. For Part 2, results a) confirmed the large RECD value for infants in the first year of life and b) showed a high degree of intersubject variability. Test retest measures of real ear aided response (REAR) gave values small enough to indicate the clear potential of probe-microphone use with infants during the hearing aid selection and fitting process. These findings should encourage attempts to carry out individual probe-tube microphone measurements with very young infants. They point to the need for infant hearing aid fitting procedures which involve such measurements to secure appropriate amplification.

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