Auditory Adaptation

Abstract

An interpretation of Békésy audiograms is presented indicating that small amplitude of excursions is due to abnormal rapid adaptation and not to a phenomenon of recruitment. The slow form of adaptation is illustrated by threshold drift of fixed-frequency tracings. The level of Békésy threshold audiograms on cases showing abnormal adaptation is shown to be dependent on the length of off-time when the stimulus is presented with various on-off ratios. Auditory flutter is also dependent on a minimum off-period. It is suggested that these phenomena are related to recovery from adaptation. Since cochlear microphonics (presumably a hair-cell phenomenon) show no reduction over time at all nondamaging intensities, adaptation is considered a ganglion-cell phenomenon. It is further postulated that adaptation in nerve lesions may be normal as in many cases of presbycusis. In such cases, the majority of nerve cells are normal. When there is significant partial injury, abnormal adaptation may be expected. Dendrite injury may be associated with abnormal rapid adaptation and axone injury to abnormal slow type.