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Abstract
The objective of this study was to compare bone-conduction (BC) auditory steady-state responses (ASSR) for infants and adults with normal hearing to investigate the time course of maturation of BC hearing sensitivity. Bone-conduction multiple ASSRs were recorded in 0–11-month-old (n=35), and 12–24-month-old infants (n=13), and adults (n=18). Low-frequency BC ASSR thresholds increased with age, whereas, high-frequency ASSR thresholds were unaffected by age except for a slight improvement at 2000Hz. Compared to adults, BC ASSR amplitudes for young infants were larger for low frequencies, whereas, their amplitudes were smaller or similar for high frequencies. Compared to adults, young infants are much more sensitive to low-frequency BC stimuli, and probably more sensitive to high-frequency BC stimuli; these differences between infants and adults persist until at least two years of age. Different ‘normal levels’ for infants of different ages must be used and are proposed in this study.
| Abbreviations | ||
| AABR | = | Automated auditory brainstem response |
| ABR | = | Auditory brainstem response |
| ANOVA | = | Analysis of variance |
| ANSI | = | American National Standards Institute |
| ASSR | = | Auditory steady-state responses |
| BC | = | Bone-conduction |
| DPOAE | = | Distortion product otoacoustic emissions |
| dB HL | = | Decibels hearing level |
| dB nHL | = | Decibels normal hearing level |
| dB SPL | = | Decibels sound pressure level |
| dB re:1µN | = | Decibels re: 1 microNewton |
| df | = | Degrees of freedom |
| DPOAE | = | Distortion product otoacoustic emissions |
| EEG | = | Electroencephalogram |
| FFT | = | Fast Fourier transform |
| F | = | Fisher's F ratio |
| ms | = | Milliseconds |
| n | = | Sample size |
| nV | = | Nano Volt |
| p | = | Probability |
| RETFL | = | Reference equivalent threshold force levels |
| SD | = | Standard deviation |
| Abbreviations | ||
| AABR | = | Automated auditory brainstem response |
| ABR | = | Auditory brainstem response |
| ANOVA | = | Analysis of variance |
| ANSI | = | American National Standards Institute |
| ASSR | = | Auditory steady-state responses |
| BC | = | Bone-conduction |
| DPOAE | = | Distortion product otoacoustic emissions |
| dB HL | = | Decibels hearing level |
| dB nHL | = | Decibels normal hearing level |
| dB SPL | = | Decibels sound pressure level |
| dB re:1µN | = | Decibels re: 1 microNewton |
| df | = | Degrees of freedom |
| DPOAE | = | Distortion product otoacoustic emissions |
| EEG | = | Electroencephalogram |
| FFT | = | Fast Fourier transform |
| F | = | Fisher's F ratio |
| ms | = | Milliseconds |
| n | = | Sample size |
| nV | = | Nano Volt |
| p | = | Probability |
| RETFL | = | Reference equivalent threshold force levels |
| SD | = | Standard deviation |
Sumario
El propósito de este estudio fue comparar las respuestas por vía ósea (BC) de estado estable (ASSR) en niños y adultos con audición normal, para investigar el proceso de maduración temporal de la sensibilidad auditiva de la BC. Se registraron respuestas múltiples ASSR por BC en niños de 0-11 meses de edad (n=35) y de 12-24 meses (n=13) además de adultos (n=18). Los umbrales de frecuencias graves ASSR para BC aumentaron con la edad mientras que los umbrales ASSR de frecuencias agudas no se afectaron por la edad excepto por una ligera mejoría en 2000Hz. Comparado con los adultos, las amplitudes BC ASSR en niños pequeños fueron más grandes en las frecuencias graves mientras que fueron menores o similares en las frecuencias agudas. En comparación con los adultos, los niños pequeños son mucho más sensibles a los estímulos por BC en las frecuencias graves y probablemente más sensibles con los estímulos por BC en las frecuencias agudas. Estas diferencias entre niños y adultos persisten por lo menos hasta los dos años de edad. Deben usarse y se proponen en este estudio diferentes “niveles normales” para niños de edades diferentes.
Notes
1. These infants were assessed using a two-channel electrode montage for the purpose of comparing ASSRs in the EEG channels ipsilateral and contralateral to the transducer (Small & Stapells, 2008). Results of an ANOVA comparing ASSR thresholds, amplitudes, and phase delays for the high-forehead-to-nape and high-forehead-to-ipsilateral-mastoid montages revealed no significant differences, consequently, data collected using the different montages were combined.
2. The present results lead to the interesting conclusion that the hypothesis put forth in the 1980s that a bone-conducted click is a ‘lower-frequency stimulus’ is likely correct for infants, but not for the reasons suggested by Weber (1983) and Yang et al (1987). In adults, the bone-conducted click does not have greater low-frequency effective spectral content compared to an air-conducted click. On the infant skull, however, the low-frequency component of the click is more effective via bone conduction than via air-conduction.
3. Although suggests that the normal level for 12–24 month-old infants should be 20 dB HL, this value was adjusted to 30 dB HL (i.e. the same as younger infants and adults) to reflect our finding that the mean bone-conduction threshold and linear regression data did not change with age at 4000 Hz.