Auditory Differences in Occupationally Noise-Exposed Workers With Normal Conventional Audiograms: A Multi-Measure Surveillance Approach

Abstract

Young adults with normal conventional audiograms may nonetheless show early noise-related auditory differences that routine surveillance misses. We evaluated a clinically feasible test battery using 280 occupationally noise-exposed workers and 100 age-matched low-noise controls (20-40 years; ≤20 dB HL at 0.5-8 kHz). Measures included conventional and extended high-frequency (EHF; 9-16 kHz) audiometry, distortion-product otoacoustic emissions (DPOAEs; 0.5-10 kHz), ipsilateral acoustic reflex thresholds (ARTs; 0.5, 1, and 2 kHz; 226-Hz probe tone), click-evoked auditory brainstem responses (ABR; wave I, wave V, and V/I ratio at 50 and 90 dBnHL), and Mandarin Bamford-Kowal-Bench speech-in-noise testing (SiN). Noise-exposed participants showed elevated ARTs at all elicitor frequencies, with the largest elevation at 2 kHz, as well as poorer EHF thresholds and lower DPOAE levels. In contrast, click-evoked ABR metrics did not differ between groups. After controlling for conventional-frequency pure-tone average (PTA4; 0.5, 1, 2, and 4 kHz) and extended high-frequency pure-tone average (PTAEHF; 9–16 kHz), lower DPOAE amplitudes were associated with higher ARTs. ARTs were not significantly associated with SiN performance, quantified as the signal-to-noise ratio (SNR) required for 50% correct recognition (SNR-50), cumulative noise exposure, or ABR measures. The noise-exposed group showed higher SNR-50 values, indicating poorer speech-in-noise performance. Within the noise-exposed group, SNR-50 was associated with PTA4 and cumulative noise exposure, whereas its association with PTAEHF was weaker and did not remain significant after correction for multiple comparisons. Together, these findings suggest that cochlear-status measures, conventional ARTs, and functional SiN performance provide complementary information beyond the conventional audiogram in occupational hearing surveillance.