Acoustic-reflex adaptation: morphology and half-life data for subjects with normal hearing.

Acoustic-reflex adaptation was studied in 35 subjects with normal hearing using nine pure-tone activators (250-6000 Hz) and a broadband-noise activator. The individual subject data generated by the 31-s activators presented 10 dB above the reflex threshold were digitized, corrected for baseline drift and ear canal volume, and analyzed in terms of the acoustic-admittance change in acoustic mmhos and in terms of the percentage of maximum-reflex magnitude. Reflex adaptation increased as a function of frequency. The adaptation functions for the lower frequencies (less than or equal to 1500 Hz) were essentially linear over the 31-s activator period, whereas the functions for the higher frequencies (greater than or equal to 2000 Hz) were curvilinear over the activator period. The experimental half-life data are compared with a theoretical half-life function that was generated to estimate normal acoustic-reflex adaptation as a function of activator frequency. Finally, the means and standard deviations are reported and discussed for (a) the onset time of adaptation, (b) the half-life time, and (c) the percentage of maximum reflex magnitude at 5-s intervals from 5 to 30 s.