Degeneration of the hearing nerve and its detection by distorted-speech testing.

A detailed description of the physiology of the auditory system (including new essential knowledge) is provided, followed by the description of five morphological levels of acoustic signal analysis, of which four play a significant part in establishing the selection capacity of human hearing. As an essential phenomenon connected with loss of the analyzing capacity of the ear, ascending degeneration of the afferent nerve fibers of the inner hair cells and of the hearing nerve (after destruction of the inner hair cells) develops. A distorted-speech test is submitted that offers a simple and easily performed calculation of a ratio, which value renders a reliable estimation of the pathological analyzing capacity of the ear caused by ascending degeneration. The test is recommended as a reliable basic component of an audiometric battery of tests.