Investigations into Neural and Perceptual Correlates of Tinnitus

Tinnitus, commonly known as "ringing in the ears", is a perception of sound without physical sound stimulation. While anybody can experience tinnitus, it commonly co-occurs with hearing loss, noise exposure, and older age. The first chapter explores the auditory brainstem response (ABR) as a potential marker for human cochlear synaptopathy, a type of "hidden hearing loss" that has been hypothesized to underlie tinnitus in listeners with clinically normal hearing. Age and hearing loss produced the expected differences in ABR measurements, but tinnitus did not produce significant differences, suggesting the clinical utility of ABR as a human biomarker for tinnitus or cochlear synaptopathy is limited. The second chapter investigates the relationship between tinnitus and external sounds; while many individuals with tinnitus complain about hearing difficulty, these same individuals often have other conditions such as hearing loss, and the relationship between tinnitus itself and external sound perception has received limited study. After controlling for age and hearing loss, listeners with tinnitus performed similarly or in some cases even better than those without tinnitus. An attention-normalization model, where attention is shared between a top-down perceptual process for tinnitus and bottom-up perception of external sounds, can both explain discrepancies between objective and subjective hearing experiences and account for the possibility that chronic tinnitus could increase auditory attention for certain low-level stimuli and actually lead to improved performance. The third chapter directly examines and models loudness perception of external sounds for listeners with and without tinnitus; at threshold, particularly, listeners with tinnitus report greater loudness perception. This is consistent with the idea that tinnitus reflects increased central noise as one aspect of overcompensation to hearing loss