Effects of chronic noise exposure on speech-in-noise perception in the presence of normal audiometry

To assess auditory processing in noise-exposed subjects with normal audiograms and compare the findings with those of non-noise-exposed normal controls.

Ten noise-exposed Royal Air Force aircrew pilots were compared with 10 Royal Air Force administrators who had no history of noise exposure. Participants were matched in terms of age and sex. The subjects were assessed in terms of: pure tone audiometry, transient evoked otoacoustic emissions, suppression of transient evoked otoacoustic emissions in contralateral noise and auditory processing task performance (i.e. masking, frequency discrimination, auditory attention and speech-in-noise).

All subjects had normal pure tone audiometry and transient evoked otoacoustic emissions amplitudes in both ears. The noise-exposed aircrew had similar pure tone audiometry thresholds to controls, but right ear transient evoked otoacoustic emissions were larger and speech-in-noise thresholds were elevated in the noise-exposed subjects compared to controls.

The finding of poorer speech-in-noise perception may reflect noise-related impairment of auditory processing in retrocochlear pathways. Audiometry may not detect early, significant noise-induced hearing impairment.