Psychoacoustic characterization of the tinnitus spectrum: implications for the underlying mechanisms of tinnitus.

In this study, an original psychometric procedure was used in order to characterize in more detail than in previous studies the different perceptual components of tinnitus, i.e. auditory sensations which are perceived in the absence of a corresponding external acoustic stimulus. Ten subjects with chronic tinnitus were asked to rate on a numeric scale the contribution of elementary pitch sensations evoked by isolated frequency components to their overall tinnitus sensation. The resulting 'internal tinnitus spectra', which represented the estimated perceptual contribution to the tinnitus sensation as a function of frequency over a large range of frequencies, were found to occupy a wide frequency range corresponding largely to that at which hearing thresholds were abnormally elevated. In most cases, they exhibited a broad peak falling within the hearing loss range. This pattern of result suggests that in subjects with high-frequency hearing loss, tinnitus sensations, when present, resemble those evoked by high-frequency noise bands with, in some cases, a superimposed tonal-like pitch. These results confirm and extend earlier results in the literature and agree with the patients' reports; their practical implications for the design of future studies on tinnitus and theoretical implications for the understanding of the neurophysiological mechanisms underlying tinnitus are discussed. The results of an additional experiment showed that the internal tinnitus spectrum could be altered by perceptual training in a fine frequency discrimination task with tones in the frequency range of the main peak of the tinnitus spectrum.