Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2009.Cataloged from PDF version of thesis.Includes bibliographical references (p. 48-50).Tinnitus, the perception of sound in the absence of an external acoustic source, disrupts the daily life of 1 out of every 200 adults, yet its physiological basis remains largely a mystery. While tinnitus and hearing loss (i.e., elevated pure tone thresholds) commonly co-occur, many people without hearing loss experience tinnitus, raising the question of whether cochlear pathology is always a prerequisite for this percept. This study used distortion product otoacoustic emissions (DPOAEs) to evaluate the cochlear amplifier of 13 tinnitus subjects and 13 non-tinnitus subjects (matched by age, sex, and audiogram) across a broad range of frequencies and intensities. DPOAE magnitudes were measured for at least 52 frequencies (500 Hz <f2 5 8 kHz, with f2ff=1.2) and nine intensities (20 dB < L2 5 60 dB, with L, = 39 + 0.4L2) in each ear. Further, this study only considered ears with normal audiograms and unremarkable history so that any abnormal findings could not be attributed large-scale hair cell damage within the cochlea. Consistent differences in the shape of the DP-gram (DPOAE magnitude as a function of presentation frequency, f2) were found in tinnitus subjects. A quantitative method for assessing DP-gram shape was developed, and statistical analyses were performed to determine whether tinnitus or other patient characteristics correlated with the abnormal DP-gram shape. The data collected in this study suggest peripheral auditory malfunction in tinnitus subjects with normal audiograms.by Leah C. Acker.S.M
