Objective tonal tinnitus

Objective tonal tinnitus (OTT) is a spontaneous and continuous narrowband acoustic signal that can be measured in many persons by placing a probe microphone in the ear canal. In a sample of thirty-two normal-hearing persons. sixteen possessed at least one OTT. These signals were most often found between 1.0 and 2.0 kHz at sound pressures in the occluded ear canal less than 200 μPa. Among several experiments with the author's own OTT at 1910 Hz was one in which the suppression of OTT by an external tone was examined. It was found that a contour of constant suppression (amplitude versus frequency of external tones that produce a criterion reduction in the amplitude of the OTT) exhibits frequency selectivity like that commonly associated with the cochlea. Objective tonal tinnitus provides a clear explanation for the phenomena connected with monaural diplacusis except for the aftertone, which does not have an observable acoustic correlate. The existence of objective tonal tinnitus of cochlear origin: (1) demonstrates that the ingredients for active biomechanical processes are present in the inner ear; and (2) suggests that such processes are employed to increase the sharpness and sensitivity of mechanical frequency analysis in the cochlea. [Work supported by NIH.]