Early Detection of Noise-Induced Hearing Loss

This study measures sounds produced by the sensory receptors of the inner ear called hair cells. These sounds are called otoacoustic emissions and one special case the investigators are studying are called distortion product otoacoustic emissions (DPOAEs) produced by presenting two tones to the ear. If the ear is damaged by noise exposure DPOAEs are reduced. In this study the investigators are attempting to improve the DPOAE test by adding a third tone to make the test more frequency specific. Whether the third tone helps will be determined by comparing DPOAEs collected with and without the third tone to clinical audiograms. If the addition of the third tone helps then the investigators expect DPOAEs tracked as a function of frequency (DP-grams) will more closely match the clinical audiograms.

The overall goal of the proposed research is to identify features of distortion product otoacoustic emissions (DPOAEs) that will eventually improve clinical methods for the early detection of noise-induced hearing loss (NIHL), which is a major sensory disability suffered by military Veterans, in particular. Toward this end, a special-purpose DPOAE measure the investigators call an augmented will be obtained. These DP-grams will test the notion that subtle post-noise changes in the DPOAE response space can be more sensitively identified when the f2 and basal source DPOAEs are isolated by the use of an interference tone (IT) and vector subtraction methods than by the commonly employed standard DP-gram procedures. The term 'augmented' maps or DP-grams was coined to describe these frequency functions when obtained with the IT present in that, under this condition, the basal source that 'fills in' or 'masks' the damage pattern is removed. The discovery of the contaminating basal source promises to modify the hearing field's current knowledge concerning the fundamental processes underlying DPOAE generation, and may also lead to the development of DPOAE tests that more sensitively identify the earliest stages of NIHL. Such tests may also be useful in Veterans, who are clinic patients and often have significant preexisting hearing losses in that higher-level primary tones can be used to increase the signal-to-noise ratio (SNR) while maintaining their sensitivity and frequency specificity. The investigators will test the ability of augmented DP-grams elicited by higher-level primary tones to uncover damaged regions in Veterans with NIHL. The notion examined here is that high-level primary tones will be more useful under conditions of preexisting hearing loss than conventional low-level primaries using the optimized augmented DP-gram by removing basal sources that come into play to obscure damaged cochlear regions as primary-tone levels are increased. Together, the combined experiments will provide a more complete understanding of the generation of DPOAEs, which will permit the creation of a useful clinical test for diagnosing and monitoring the development of NIHL.

Eligibility Criteria:
Inclusion Criteria:

* Veterans 18-65 years old

Exclusion Criteria:

* Individuals with no measurable distortion-product otoacoustic emissions (DPOAEs) since the goal of the study is to relate DPOAEs to hearing function