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Re: Auditory efferents and phase locking


I'm not among those who think the efferent feedback is merely protective, but it's a possibility. When there's no efferent feedback to turn them down, the OHCs just work as hard as they can, which saturates at high enough levels.

Presbycusis is largely a lack of OHC activity, whether it's modulated by efferent feedback or not. Loss of OHCs or their ability to provide amplification causes a huge loss of gain, and corresponding threshold elevation. Along with this comes a reduction in "compression", which would also be expected from lack of efferent feedback, but that's a somewhat more subtle effect. Still, it's surprising to me that people haven't found a good way to assess the effect of missing the feedback.


At 11:33 AM +1000 9/1/11, Matt Flax wrote:
I understand this point of view, that gain-control is primarily
protective ... if you follow that line of literature and theory, we have
the classical view of hearing ... augmentation of the passive travelling
wave to get the active travelling wave. Where local amplification away
from the best frequency acts to restrict movement... to protect.

In this argument, we can only assume that emissions occur from backwards
travelling waves ... do you agree - or am I jumping the gun like Usain
Bolt (2011 - world championships) ?

So here I sever the classical view from the non-classical view.

We have to turn back to experiments which look at how the waves travel
in the Cochlea.

Ren.T. clearly shows (in most of his body of work) forward active
travelling waves (in the base). Wilson (1980) agrees with him. Ruggero
similarly is most likely in agreement [1].

And all of this is in the base of the Cochlear ... what happens in the
apex is a toatally different story.

p.s. If it was to protect, then why is Presbycusis so bad ?

[1] Ruggero, M.A., "Comparison of group delays of 2f- f distortion
product otoacoustic emissions and cochlear travel times", Acoustics
Research Letters Online 5 (2004), pp. 143.

On Wed, 2011-08-31 at 16:54 -0700, Richard F. Lyon wrote:
 Perhaps the
 gain-control role is primarily protective, as many have speculated?