Tone Decay Test in Neuro-Otological Diagnosis

The tone decay test was carried out upon normal subjects and patients with a variety of pathological conditions. With normal hearing and conductive deafness, tone decay termed type I was minimal and never exceeded 15-dB. In endorgan deafness type I predominated but a few exhibited slightly greater decay termed type II. Type IV, in which the threshold elevation was severe and rapid, was a characteristic finding in 15 subjects with nerve fiber lesions, including 12 with cerebellopontile angle tumors. Of 52 patients with brain stem lesions a well marked, but slow rate, tone decay type III, was found in a significant proportion including a number with normal hearing. In the latter, good correlation was established between lateralization of the lesion effected by the caloric and the tone decay tests.