Clinical Utility of a Tamil SIN Test in Tinnitus with Normal Audiograms: Insights from Behavioral and Electrophysiological Measures

IntroductionTinnitus, the perception of sound without an external source, is a common auditory disorder that may occur even in individuals with normal hearing. Such cases are often associated with Hidden Hearing Loss (HHL), involving suprathreshold deficits linked to cochlear synaptopathy and neural dysfunction, undetectable by standard audiometry. Speech-in-noise (SIN) testing, particularly in the listener’s native language, along with objective measures like otoacoustic emissions (OAEs) and auditory brainstem responses (ABRs), can help uncover these deficits.This study evaluated the clinical utility of a validated Tamil SIN test in detecting hidden auditory deficits in individuals with tinnitus and normal hearing, supported by electrophysiological measures including OAE fine structure and ABR.Materials and MethodsFifteen adults with chronic bilateral tinnitus and 15 age- and gender-matched controls with normal hearing participated. SIN performance was assessed using a validated Tamil sentence-in-noise test. The electrophysiological assessment included transient evoked otoacoustic emissions (TEOAEs), distortion product otoacoustic emissions (DPOAEs), and auditory brainstem responses (ABRs). Group comparisons were made using independent-sample t-tests.ResultsCompared to controls, the tinnitus group demonstrated significantly higher SNR-50 thresholds and greater SNR loss in the Tamil SIN test, indicating impaired speech-in-noise recognition. DPOAE amplitudes were markedly reduced across mid- to high-frequency ranges, suggesting subclinical cochlear dysfunction. ABR results revealed prolonged absolute latencies of Waves I and III and elevated interaural latency differences of Wave V, consistent with early neural conduction abnormalities. All key differences were statistically significant (p < 0.05), supporting the presence of suprathreshold auditory deficits in tinnitus patients with clinically normal hearing.ConclusionThis study confirms that individuals with tinnitus and normal audiograms exhibit both behavioral and electrophysiological signs of hidden hearing loss. The Tamil SIN test, when used alongside DPOAE and ABR, offers a sensitive and language-appropriate tool for detecting subclinical auditory dysfunction. These findings underscore the need to incorporate suprathreshold testing in routine audiological evaluations of tinnitus, even when standard thresholds are within normal limits.