Use of probe tube microphone measurements in hearing aid selection for children: some initial clinical experiences

An objective bone conduction verification tool using a piezoelectric thin-film force transducer

All hearing aid fittings should be validated with appropriate outcome measurements, whereas there is a lack of well-designed objective verification methods for bone conduction (BC) hearing aids, compared to the real-ear measurement for air conduction hearing aids. This study aims to develop a new objective verification method for BC hearing aids by placing a piezoelectric thin-film force transducer between the BC transducer and the stimulation position. The newly proposed method was compared with the ear canal method and the artificial mastoid method through audibility estimation. The audibility estimation adopted the responses from the transducers that correspond to the individual BC hearing thresholds and three different input levels of pink noise. Twenty hearing-impaired (HI) subjects without prior experience with hearing aids were recruited for this study. The measurement and analysis results showed that the force transducer and ear canal methods almost yielded consistent results, while the artificial mastoid method exhibited significant differences from these two methods. The proposed force transducer method showed a lower noise level and was less affected by the sound field signal when compared with other methods. This indicates that it is promising to utilize a piezoelectric thin-film force transducer as an in-situ objective measurement method of BC stimulation.

Real ear to 6-cm3 coupler differences in young children

Real-ear sound pressure levels under supra-aural earphones were measured for a group of young children (9 months to 7 years) and adults. Pure-tone signals were presented at nine test frequencies from 250 to 6000 Hz, and real ear to 6-cm3 coupler differences were computed for each frequency. Results suggest that, by 2 years of age, average real ear to 6-cm3 coupler differences are similar for adults and children. The intersubject variability for all groups supports the need for real-ear threshold measures on an individual basis in cases where the ability to amplify the speech spectrum to a level that is audible across the frequency range is in question.

Probe-tube microphone measurements with very young infants

The practicalities of performing probe-tube microphone measurements in a clinical environment with unsedated infants were examined. External ear resonance curves (unaided response) were obtained for both ears of a group of infants aged 0-6 months and an adult comparison group. A repeat measure (with probe-tube repositioning) was made to estimate the test-retest reliability of these measures. Results showed that the mean infant resonance frequency (4200 Hz) occurred at a significantly (P less than 0.005) higher frequency than the mean adult resonance frequency (2950 Hz). Infants test-retest differences for resonance frequency (mean = 286 Hz, s.d. = 404 Hz) and size of peak (mean = 2.2 dB, s.d. = 2.6 dB) showed acceptable stability for the measurements. Size of resonance peak was found to vary positively with ear canal volume; however, estimation of ear canal volume from tympanometry did not provide a useful indicator of the size of the peak. The probe-microphone measurements were found to be feasible, repeatable and practical with these infants.