Hi Mark, list,
Even though not being an expert in tinnitus myself (but recently got attracted to it), I think I could add two pieces of information here:
- There is this (pretty fantastic) paper:
Kujawa, S. G., and Liberman, M. C. (2009). “Adding insult to injury: cochlear nerve degeneration after
temporary noise-induced hearing loss,” J. Neurosci. 29, 14077–14085.
that shows that there might be a connection between noise trauma, (not easily detectable) hearing loss and tinnitus. Some of these implications will probably also apply once the damage is more severe. Based on this paper we did a study that indicates also implications for supra-threshold hearing (Epp et al., J. Acoust. Soc. Am. 132 (3), EL196 ). You might also want to check out the references...they might aim at what you are looking for.
- You idea about the dip in the audiogram: Depending on the level you see in the audiogram, this might indeed be an "artifact" of the poor frequency resolution of audiograms, neglecting fine structure effects when assessed with pure tones. SOAEs are also (always) associated with a region of high sensitivity (i.e. up in the audiogram) - but they are most likely not a source of tinnitus. If you mean by "dip" a poor sensitivity, then there might be what is being discussed as "deafferentiation" going on (see above) - with implications still to be clarified.
The distinction between a hearing loss and masking by you tinnitus as the source of the dip in the audiogram is hard to define: The audiogram defines your ability to detect a tone - testing the whole auditory pathway rather than just parts of it. So by definition it is some kind of hearing loss if you can't detect a tone close to your tinnitus...no matter what the reason is.
These just as some additional thoughts
All the best
On 09/09/12 11:09, Mark Fletcher wrote:
I've noticed that tinnitus researchers often talk about the frequency of tinnitus being at a dip in the audiogram (in some people). It's then said that tinnitus, therefore, occurs at the frequency of a hearing loss. Even if I could be said to have an area of expertise, tinnitus research wouldn't be it, but it's certainly an area of interest for me and I am someone with tinnitus who has done several audiograms. On my audiogram there is a dip around the frequency of my tinnitus, but I suspect this dip is due to masking of the tone or warble used rather than necessarily being indicative of a hearing loss. I'd be very interested to know how people make the distinction between masking by tinnitus and a hearing loss.
Institute of Hearing Research, Nottingham