Displacement of the malleus in neonatal golden hamsters

A capacitive probe was used to measure displacements of the umbo of the malleus in neonatal golden hamsters for discrete frequencies from 0.6 to 35.0 kHz. Displacement, extrapolated to a sound pressure of 100 dB SPL, plotted as a function of frequency demonstrated low-pass characteristics with a cutoff frequency near 9.0 kHz. The amplitude of displacement increased with age to a plateau at all frequencies. Analysis of the data below the cutoff frequency indicated that low frequency displacements were dominated by a compliance which increased with age. It was also found that high frequency responses showed evidence of increased mass limitation in younger as compared with older subjects. Comparisons between the inverse of velocity and evoked response threshold curves indicated that the middle ear plays an important role in determining thresholds throughout development.