Ear-canal impedance and reflection coefficient in human infants and adults

Abstract

The ear-canal impedance and reflection coefficient were measured in an adult group and in groups of infants of age 1, 3, 6, 12, and 24 months over frequency range 125-10,700 Hz. The development of the external ear canal and middle ear strongly affect input impedance and reflection coefficient responses, and this development is not yet complete at age 24 months. Contributing factors include growth of the area and length of the ear canal, a resonance in the ear-canal walls of younger infants, and a probable influence of growth of the middle-ear cavities. The middle-ear compliance is lower in infants than adults, and the middle-ear resistance is higher. The power transfer into the middle ear of the infant is much less than into that of the adult. Such differences in power transfer directly influence both behavioral and physiological measurements of hearing. The difficulties of interpretation of neonatal tympanograms are shown to be a consequence of ear-canal wall vibration. Impedance and reflectance measurements in the 2-4-kHz range are recommended as a potentially useful clinical tool for circumventing these difficulties.

Specification of absorbed-sound power in the ear canal: Application to suppression of stimulus frequency otoacoustic emissions

“…À6 dB for every ear. The tendency for all the percentiles of L F0 to increase above 6 kHz was due to an increase in jRj at this frequency range, as further discussed below and consistent with previous group measurements of jRj 2 (e.g., Keefe et al, 1993). The phase of the transfer-function H F0 for the percentiles shown in the lower panel of Fig.…”

“…Ear-canal wall losses are important below 1 kHz in young infants (Keefe et al, 1993); they are detectable, but remain small, below 0.4 kHz in adults [Fig. 5(b) in Margolis et al, 1999].…”

“…The power W a absorbed from an acoustic stimulus presented in an ear canal with acoustic admittance Y ¼ G þ jB and mean-squared total pressure jPj 2 /2 at the probe is (Keefe et al, 1993)…”

Effects of Bone Oscillator Coupling Method, Placement Location, and Occlusion on Bone-Conduction Auditory Steady-State Responses in Infants

“…Alternatively, if there is low-frequency energy trapped in the occluded infant ear (similar to adults), it may be absorbed by the infant's compliant ear canal wall (Keefe et al, 1993(Keefe et al, , 1994, resulting in no net increase in energy passing through to stimulate the cochlea. These preliminary results suggest that there is no effect of occlusion in infants younger than 6 mo of age; however, further studies should be conducted in a larger group of infants to confirm these findings.…”

Modeling Ear-Canal Acoustics, Incorporating Visco-Thermal Effects and the Influence of the Middle Ear

“…The agreement between the middle ear input impedance calculated in this study and that of O'Connor and Puria [8] further validates the suggestion that viscous and thermal losses contribute significantly to ear canal acoustics. Further studies that are suggested include quantifying visco-thermal effects in infant ear canals where the walls of the ear canal are more compliant than in adults [4], and the effect of speaker/microphone location in the ear canal on visco-thermal losses [14].…”