Supra-threshold deficits in normal hearing military recruits exposed to impulse noise.

The aim of this study was to determine the effect of impulse noise exposure on various proxy measures of cochlear synaptopathy in young military recruits. A total of 27 military recruits with exposure to firearm and artillery noise and 13 non exposed participants were recruited. All presented with normal hearing thresholds and the presence of distortion product otoacoustic emissions (DPOAEs). The Noise Exposure Structured Interview (NESI) was used to quantify noise exposure. Speech perception in noise (SPiN), equivalent rectangular bandwidth (ERB) of auditory filters, auditory brainstem response wave I amplitude, wave I amplitude growth function, wave I/V amplitude ratio, wave V latency, wave V latency shift with ipsilateral noise, and the summating potential/action potential ratio of the electrocochleography were measured. In military participants, SPiN was worse, ERB at 4 kHz was larger, wave I amplitude at 75 dBnHL was reduced, and wave V latency was delayed. However, no significant correlations were observed between NESI and auditory measures, once multiplicity of tests was controlled for. These results suggest that military recruits may exhibit supra-threshold deficits, despite presenting with normal hearing thresholds and presence of DPOAEs. Future studies should include a measure of auditory filters in their test battery.