Early Detection of Noise-Induced Hearing Loss

• DP-gram with interference tone 1/3 octave above f2 [ Time Frame: At the end of the testing session ] [ Designated as safety issue: No ]
  

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 we 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. We 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.