Middle ear development. I: Extra-stapedius response in the neonatal chick.

A laser interferometry system was used to study the ontogeny of tympanic membrane mechanical responses to sound as measured at the tip of the extra-stapedius (ES) in chicks. The ES velocity and phase responses in the frequency range between 0.2 and 10.0 kHz were measured in animals ranging from 3 days of age to adult. The slope of the low frequency response remained constant with age while the ES low frequency sensitivity increased by 11 dB. The sensitivity improvement indicated an increase in low frequency middle-ear admittance. However, there was no consistent developmental improvement in high frequency ES sensitivity. Comparisons between the growth of low frequency ES velocity, the development of admittance magnitude, and evoked potential threshold sensitivity developmental data indicated no clear relation between these measures.