ELSEVIER Hearing Research 80 (1994) 216-232 Neurophysiological model of tinnitus: Dependence of the minimal masking level on treatment outcome Pawel J. Jastreboff a,*, Jonathan W.P. Hazell b, Rena L. Graham b a University of Maryland School of Medicine, Department of Surgery, 10 South Pine Street, MSTF Building, Room 434F, Baltimore, MD 21201, USA b RNID Medical Research Unit, ILO with the Ferens, University College London, London, UK Received 8 February 1994; revised 1 August 1994; accepted 14 August 1994 Abstract Validity of the neurophysiological model of tinnitus (Jastreboff, 1990), outlined in this paper, was tested on data from multicenter trial of tinnitus masking (Hazell et aI., 1985). Minimal masking level, intensity match of tinnitus, and the threshold of hearing have been evaluated on a total of 382 patients before and after 6 months of treatment with maskers, hearing aids, or combination devices. The data has been divided into categories depending on treatment outcome and type of approach used. Results of analysis revealed that: i) the psychoacoustical description of tinnitus does not possess a predictive value for the outcome of the treatment; ii) minimal masking level changed significantly depending on the treatment outcome, decreasing on average by 5.3 dB in patients reporting improvement, and increasing by 4.9 dB in those whose tinnitus remained the same or worsened; iii) 73.9% of patients reporting improvement had their minimal masking level decreased as compared with 50.5% for patients not showing improvement, which is at the level of random change; iv) the type of device used has no significant impact on the treatment outcome and minimal masking level change; v) intensity match and threshold of hearing did not exhibit any significant changes which can be related to treatment outcome. These results are fully consistent with the neurophysiological interpretation of mechanisms involved in the phenomenon of tinnitus and its alleviation. Keywords: Tinnitus; Neurophysiological model; Psychoacoustics; Treatment 1. Introduction At the present time we do not have any objective, physical measurement that can be related to the pres- ence of tinnitus. Tinnitus is an auditory phantom per- ception, and therefore cannot be associated with any sound measurement. Characterization of tinnitus for diagnosis and monitoring of the effectiveness of treat- ment has been performed mainly by subject interview, and extensive questionnaires have been invented for this purpose (Erlandsson et aI., 1992; George and Kemp, 1991; Kuk et aI., 1990; Hazell et aI., 1985; Wilson et aI., 1991). This approach yielded important epidemiological and demographic data but failed to provide measures useful for predicting the outcome of * Corresponding author. Fax: (410) 706-4004; e-mail: pjastreboff@surgery1.ab.umd.edu 0378-5955/94/$07.00 © 1994 Elsevier Science B.V. All rights reserved SSDI 0378-5955(94)00134-0 treatment and monitoring its progress (Coles et aI., 1993; Stouffer and Tyler, 1990). At the same time much importance has been at- tached to the psychoacoustical description of tinnitus (Penner and Bilger, 1992; Kodama and Kitahara, 1990; Penner, 1986; Hazell et aI., 1985; Tyler and Conrad- Armes, 1984; Penner, 1983b; Tyler and Conrad-Armes, 1983a; Hazell, 1981; Penner, 1988a; Penner, 1988b; Penner, 1983a; Tyler and Stouffer, 1989; Tyler and Conrad-Armes, 1983b; Penner and Klafter, 1992). The expectation was that by evaluating tinnitus pitch, loud- ness, maskability, and reconstructing the tinnitus sound, different tinnitus categories could be identified for diagnosis and prediction of treatment effectiveness (Douek, 1981). Unfortunately clinical results up to date have failed to find significant correlations between psychoacoustical description of tinnitus and the treat- ment outcome (Hazell et aI., 1985). First, it turned out that, paradoxically, patients with