I think the authors touch on this in their discussion:

"It has been shown that high-level and long-duration acoustic trauma (at an intensity level of 115 dB SPL for 2 h) induces widespread damage to the stereocilia, mainly those on the inner hair cells and first row of the outer hair cells (Liberman, 1987). Acoustic trauma is also known to induce hair cell and neuron death through formation of reactive oxygen species and free radicals (Duan et al., 2000; Lefebvre et al., 2002). It has been suggested that necrosis and apoptosis are simultaneously involved in hair cell death (Hu et al., 2002). The resulting hair cell death and lesions are assumed to be permanent in mammals (Duan et al., 2000). In addition, acoustic trauma causes a degeneration of auditory nerve fiber neurites through excitotoxicity."

As with many types of injury, the mechanisms initiated by the injury (ie apoptosis, ROS, excitotoxicity etc) spread away from the initial injury site to affect surrounding cells. Perhaps this could answer your question?

"...Exposure to less intense noise (i.e., < 90 dBA) for short durations (i.e., ≤ 24 hrs) may result in a mild (< 30 dB) temporary hearing loss (Mills et al., 1970; Melnick, 1976). A noise-induced temporary hearing loss, or temporary threshold shift (TTS), is characterized by an increase in the hearing thresholds at some frequencies immediately following exposure, depending on the frequencies comprising the noise and its intensity. The threshold shift generally disappears within 24–48 hours after the exposure terminates (Mills et al., 1970; Melnick, 1976). Typically, exposure to more intense noise (> 90 dBA) or moderate noise for longer durations (> 24 hours) results in a larger amount of TTS (i.e., > 40 dB). In these cases, postexposure improvement of thresholds may continue for 30 days or longer, but in general, thresholds will not return to preexposure values. The individual likely will be left with a residual permanent threshold shift (PTS) (Taylor et al., 1965; Mills and Talo, 1972; Mills, 1973; Henderson et al., 1974a; Henderson and Hamernik, 1982)."

http://www.nap.edu/openbook.php?record_id=11443&page=38

It's a rather well known effect in human audiology, due to non linear dynamics of cochlea: the low frequencies in industrial noise cause a "notch" in high frequencies hearing thresholds - it's a relation in octaves.

Indeed it's not so common in literature investigating in high frequencies like you're doing : good to do so. Also in humans we often have high frequencies misknown loss linked to more usually detected NIHL notch at 3-6KHz

Luis, from our work of more than 30 years ago--too far back to offer you any links, we found several aspects that would create the problem of greater frequency-band damage from narrow acoustic trauma that might be helpful. The most obvious is that encountered by the Place Theory, whereas a traveling wave over both the scala vestebuli and scala media creates a hydraulic violence that exceeds the ability of the areas of mechanical action (tectorial membrane, tiplink hair cell connections, and outer hair cells) to withstand. This would affect every frequency of the entire auditory tube, including past the helicotrema.

Another aspect to consider is the affect on spiral gangion when certain bands of sound exceed 127dB--this happens because even though the input amplitude may be only 120dB, the accelerating aspect of the traveling wave and override of the tensor tympani at the TM.

Another area that we noticed (much later, in the early 1990s) were the limbic symstem aspects: A 4KHz tone, for instance, which is also close to the human heart sinus node tone that stimulates the vagus, is the most sensitive area in human hearing and sets off a number of sypathetic (and parasympathetic) autonomic responses at various junctures of the human body, especially the pericardial sac of the heart. This, through a different avenue, reduce or stimulate (depending upon intensity) CNS involvement that affect hearing levels--I am thinking the vascularization of the stria vascularis and its role in auditory perception.

Finally, harmonic aspects (at the octave and seme-octave) have been noted to reinforce the traveling wave, so that more than just the fundamental frequencies were affected--this could extend into both overtones (on the way to the fundamental itself) and beyond the fundamentals into the apical lower harmonics (aka undertones). These reinforced harmonics help us understand how the ear tempers a piano string as it is being tuned (aka "The well-tempered claviar").

I hope this provides some insight into your question. The ear is an amazing piece of biological/chemical engineering, as I am sure current researchers of the human hearing system are discovering.

Also remember, the position of maximum stimulation of the basilar membrane and , therefore the organ of Corti depends upon the intesity of the signal. As the intensity of the sound increases from threshold (the intensity at which the frequencies are mapped), the maximum point of vibration moves towards the base of the cochlea (which is mapped to higher frequencies) due to physical properties of the membrane (mass, elasticity, etc.). To study the damage caused by a high intensity sound you map the damage with your low intensity (threshold) sounds so the damage appears to be occuring at higher frequencies.

Excellent reply, Karen.

NICE answers! I immediately thought of the finger in the water that has much more influence than in the immediate plunge. Physics is SO fascinating. I've been recently reading about the possibility of ultrasound causing autism via impact on cell disturbance. Also fascinating, -- this also brought that to mind. So what if ultrasound also causes hearing abnormalities in utero, along with or without the resulting autism? Yes, I know that's another question, but I think it's all interesting...

Interesting question, Sandra--we know that a number of things relative to mother's health (acidosis, smoking, alcohol, drugs, pain killers, NSAIs, steroids, Aspertame, and more recently we are looking at high fructose corn syrup) contributing to underlying in utero factors that can bring autistic/developmental delay conditions.

I sure wish we'd figure it out. I'm still in the K-12 environment and what I see daily is heart-wrenching. Being a highly reactive person to chemistry myself, I had my thoughts fixed on that factor, but find this new idea added one more that we may not see or consider. The numbers just keep growing. I had to resign a job due to pesticides sprayed in my room and making me sick. The new teachers and kids still met there. One of my students had a 5 lb baby and so did her friend. I wonder about foul chemistry all the time. If you should ever need a "nose" to establish presence of chemicals, just let me know! (partially kidding) I have only increased in sensitivity and am surprised at how many don't notice it. Poor kids. Nice to chat with you.

Thank you all for your answers!! Very helpful and informative!

I have an additional question and remark:

Question:

Given the mechanism of non-linear wave propagation in the cochlea, why do we only hear/perceive 5kHz, if the basilar membrane (and organ of Corti) is being excited even more at locations corresponding to higher frequencies (all the way out to 24kHz)?

Remark:

I suppose this nonlinear propagation and stimulation is the reason why, with age, people invariable have some high frequency loss -- that part of the basilar membrane and organ of Corti suffer greater cumulative wear and tear. Related, I read somewhere (can't find reference now) that bushmen of the Kalahari Desert do not experience age-related hearing loss, because they are never exposed to loud noises throughout their lifetime. (In searching for the reference, I found http://phys.org/news/2011-03-genetic-analysis-modern-humans-evolved.html, where they claim that modern humans descend from the bushmen. It seems our hearing was not designed for modern day noises!!!)

Thanks again for all your thoughts!

I mostly agree with your remark, Luis, while I must "better understand" your question:

first, remind we started from your chinchilla and human hearing&listening , as Professor Chartrand marvellously resumed, is "a bit more complex".

If 120 or 128 dBSPL in ABR is a huge click, Mozart or Bach are much different stuff to our cochlea and hearing central pathways, both main and accessory, in harmonics and subharmonics and averaging of complex vibration patterns.

As to humans, we hear/perceive almost always up to 14KHz, if you check normal people with high frequencies audiometry, even most of those already showing a notch, a loss in 2-8KHz.

Many people, i.e. musicians, easily recognize sound stimuli up to 20KHz : remind that audiometry is simply a sensation-perception-motion reaction arch, so the more you're accustomed to listen to sounds the better you' ll recognize sound stimuli

But if you mean "why I hear 5KHz while my cochlea is stimulated in a wider range of frequencies?" is simply because you "don't hear " with your cochlea but with your brain : tonotopism is the mechanism which "focus" our hearing perception on the prevalent, more redundant sound... So you hear 5KHz

Beg you pardon, you're dealing with cats, not chinchillas, but it doesn't change too much