Emerging characteristics of the acoustic reflex in infants.

One hundred ninety-nine infants (birth to 15 weeks) were administered an impedance battery to describe emerging characteristics of the acoustic reflex in this age range. Tympanometry results suggest that the middle ear system changes from a highly flaccid state at birth to a relatively normal compliance by 15 weeks. Acoustic reflexes were observed infrequently in the newborn population and gradually increased as a function of age, but never exceeding 43% of the ears tested. A conservative approach regarding the relevance of the presence of the reflex in young children is warranted.