Clinical Utility of the Tamil Speech-in-Noise Test for Detecting Hidden Hearing Loss in Tinnitus with Normal Audiograms: Insights from Behavioral and Electrophysiological Measures

Abstract

Background and Aim: Tinnitus often occurs in individuals with normal audiograms and may reflect Hidden Hearing Loss (HHL). Conventional audiometry fails to detect these suprathreshold deficits. This study evaluated the clinical utility of a validated Tamil Speech- in-Noise (SIN) test, supported by Otoacoustic Emissions (OAEs) and Auditory Brainstem Responses (ABRs), in detecting HHL in tinnitus patients.

Methods: Thirty native Tamil-speaking adults were recruited: 15 with chronic bilateral tinnitus and 15 matched controls. All had normal hearing thresholds. Participants underwent the Tamil Speech-in-Noise (SIN) test, Transient Evoked Otoacoustic Emissions (TEOAEs), Distortion Product Otoacoustic Emissions (DPOAEs), and click-evoked Auditory Brainstem Response (ABR). Group differences were analyzed using independent-sample t-tests.

Results: The tinnitus group showed significantly higher Signal-to-Noise Retios at 50% correct (SNR-50) values and Signal-to-Noise Ratio (SNR) loss compared to controls, indicating impaired SIN perception. Both DPOAEs and TEOAEs were significantly reduced across frequencies, confirming cochlear dysfunction despite normal audiograms. ABR analysis revealed delayed wave I and wave III latencies, with marginal prolongation of wave V, indicating early auditory nerve involvement.

Conclusion: Tinnitus patients with normal audiograms demonstrate measurable auditory deficits, reflecting HHL. The Tamil SIN test, complemented by both OAE and ABR, provides a culturally appropriate and sensitive protocol for early detection. These findings highlight the limitations of pure-tone audiometry and support integrating multimodal assessments into tinnitus evaluations.