PROBE-TUBE MICROPHONE MEASURES WITH VERY YOUNG INFANTS - REAL EAR TO COUPLER DIFFERENCES AND LONGITUDINAL CHANGES IN REAL EAR UNAIDED RESPONSE

Objective: 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). Design: Part 1 is a longitudinal study involving 12 infants. Serial measures of REUR were obtained over an 18-mo period. Infants were less than or equal to 3 mo for the first test and less than or equal to 21 mo at the last t est visit. Practicalities of probe-tube microphone testing of unsedate d 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 ver sus coupler gain was made. Test-retest differences for real ear aided response were estimated. Results: Part 1 results indicate that probe-t ube microphone measures in unsedated infants are feasible and show goo d within-subject repeatability. REUR measures for the more alert and m obile older subjects, as for the younger infants, showed an acceptably small degree of intersubject variability. The frequency of the primar y 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 fl uctuation in the frequency of the REUR peak. For Part 2, results a) co nfirmed the large RECD value for infants in the first year of life and b) showed a high degree of intersubject variability. Test retest meas ures of real ear aided response (REAR) gave values small enough to ind icate the clear potential of probe-microhone use with infants during t he hearing aid selection and fitting process. Conclusion: These findin gs should encourage attempts to carry out individual probe-tube microp hone measurements with very young infants. They point to the need for infant hearing aid fitting procedures which involve such measurements to secure appropriate amplification.