Low-Sound-Level Auditory Processing in Noise-Exposed Adults
Résumé
Few studies have explored the relationship between noise exposure and auditory processing at low sensation levels (SLs). Contra-indicative results from these studies may be due to one or some of: insensitive measures; poor quantification of noise exposure; or a lack of a developed hearing loss. The current study aimed to control better for these possible confounds. Thirty-five participants between the age of 30 and 75 years were recruited, with normal or near-normal absolute thresholds up to 1 kHz and a mild-to-moderate threshold elevation between 3 and 6 kHz. Their lifetime noise exposure was estimated using a structured interview (NESI, Guest et al., 2018). The NESI score was used to categorise participants into Low-, Medium- or High-Noise groups (LN, MN and HN). Psychophysical measures of absolute threshold (AbsTh) were followed by measures of frequency difference limens (FDLs) and AM discrimination (AMdis). The experiments were performed at five centre frequencies (0.75, 1, 3, 4 and 6 kHz) and at both 15 and 25 dB SL. As expected, the FDL was significantly worse at 4 and 6 kHz when compared to the lower frequencies. No effect of lifetime noise exposure was observed. Post-hoc analysis showed that participants with no music experience had the worst performance, suggesting a possible confound. The AMdis threshold was lower (better) at 25 dB SL compared to 15 dB SL. There was also an interaction with NESI grouping: At 25 dB SL (but not at 15 dB SL), the HN group showed a lower threshold than the LN group. Finally, a strong negative correlation existed between NESI score and AMdis threshold at 6 kHz and 25 dB SL; even after controlling for music experience, AbsTh at 6 kHz and age. These findings suggest more of an outer rather than an inner hair cell dysfunction due to noise exposure.
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