Objective: To evaluate whether cochlear synaptopathy is a common pathophysiologic cause of tinnitus in individuals with normal audiograms. Study Design: Prospective study. Setting: Tertiary referral center. Methods: We enrolled 27 subjects with unilateral tinnitus and normal symmetric hearing thresholds, and 27 age- and sex-matched control subjects with normal symmetric hearing thresholds. We measured 1) the amplitudes of waves I and V with 90 dB nHL click stimuli in quiet conditions; 2) the latency shift of wave V with 80 dB nHL click stimuli in background noise, varying from 40 dB HL to 70 dB HL; and 3) uncomfortable loudness levels (UCLs) at 500 Hz and 3000 Hz pure tones. Results: There were no significant differences in the wave V/I amplitude ratio or the latency shift in wave V with increasing noise levels among the tinnitus ears (TEs), nontinnitus ears (NTEs), and control ears. There were no significant differences in UCLs at 500 Hz or 3000 Hz between TEs and NTEs, but the UCLs were lower in TEs (mean 111.3 dB or 104.1 dB) and NTEs (mean 109.4 dB or 100.6 dB) than in control ears (mean 117.9 dB or 114.1 dB, p  < 0.017). No subject met our criteria for cochlear synaptopathy or increased central gain in terms of all three parameters. Conclusion: Based on these results for UCL, increased central gain is a major mechanism of tinnitus in humans with normal audiograms. However, this compensatory mechanism for reduced auditory input may originate from other pathophysiologic factors rather than from cochlear synaptopathy.

Background and Objectives: Hearing aids (HAs) with built-in sound generators can alleviate the discomfort of tinnitus in individuals with tinnitus and impaired hearing. However, it is unknown how tinnitus-control sound (TCS) affects speech perception in HA users. Therefore, this study aimed to evaluate the effect of HA TCS on auditory spectral resolution, temporal resolution, and speech perception in individuals with tinnitus and impaired hearing. Materials and Methods: The subjects were 13 elderly listeners (62.38±8.44 years, seven males, six females) with tinnitus and impaired hearing who had been using a receiver-in-canal HA with a built-in sound generator in everyday life for more than 3 months. The following psychoacoustic measurements were performed: spectral-ripple discrimination (SRD), temporal modulation detection (TMD), and speech recognition threshold in noise. The results obtained with HA-only and HA plus TCS conditions were compared. Results: There were no significant differences in SRD and TMD between the HA-only and HA plus TCS conditions (p>0.05). However, the HA plus TCS conditions were associated with worse speech recognition than the HA-only conditions (p=0.027). Conclusions: TCS constrains speech perception in noise in individuals with tinnitus and impaired hearing, implying that the TCS introduces additional noise to existing tinnitus. Therefore, we recommend that individuals with tinnitus who use a HA with a built-in sound generator should turn off the sound generator in daily life, especially in noisy environments.

Background and Objectives We investigated whether there are differences in auditory performance between the healthy ears of subjects with unilateral deafness (UD) and the control ears of subjects with normal hearing (NH) in both ears.Subjects and Method Sixteen subjects with acquired UD and 16 subjects with NH thresholds for both ears were enrolled. We compared the auditory performance of UD group and control group with NH in both ears.Results We found no meaningful differences in the three measures of psychoacoustic performance between the total healthy ears of subjects with UD and the ears of the control group. However, in the subgroup comparison, the left ears of subjects with right UD showed significantly poorer spectral-ripple discrimination (SRD) than the right ears of the subjects with left UD (<i>p</i>=0.006) and the ears of control subjects with NH (<i>p</i>=0.004).Conclusion Our findings indicate that after unilateral auditory deprivation, auditory processing is differentially affected by the side involved. In the subjects with acquired UD, the longterm hearing deprivation on the right side induced the down-regulation of central auditory process for SRD, but hearing deprivation on the left side did not affect SRD.