Such_Saturation
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Now hear this: Simple fluid waveguide performs spectral analysis in a manner similar to the cochlea
"Current dogma in inner-ear mechanics states that the peaking is caused by a form of biological amplification that injects mechanical energy into the sound-evoked wave," van der Heijden continues, "but I'm skeptical about the existence of what is customarily termed a cochlear amplifier." His position makes sense, since after 35 years the evidence for amplification is still circumstantial at best, and experts disagree on the basic mechanisms. "Amplification requires phase-locked mechanical feedback to high-frequency input – as high as 100 kHz for bats and dolphins – which is physiologically very implausible." Moreover, he points out, it serves no known purpose: In order to amplify faint sounds, you need to detect them in the first place – so why not stop there if your aim is to hear the sound? "You might think that amplifying faint signals improves their detectability, but that is not the case. Amplifiers always worsen the signal-to-noise ratio."
An alternative to amplification – the one that van der Heijden has taken – is focusing available sound energy. "In a wave this is done by slowing it down, which causes a traffic jam-like congestion of the energy. In addition, from measurements we know that by the time the vibrations are converted to neural signals, the speed of the energy transport has slowed down to a mere walking pace. No amplifier needed!" In fact, in vivo experiments by van der Heijden and his former PhD student Corstiaen Versteegh showed that deceleration is steep, giving sharp peaking. "However," van der Heijden emphasizes, the question now becomes, What is the physics behind the steep wave deceleration?" In the paper, van der Heijden notes that he expects that these new data and ideas will help them to understand the basis of cochlear frequency selectivity and gain control in the near future.
"Current dogma in inner-ear mechanics states that the peaking is caused by a form of biological amplification that injects mechanical energy into the sound-evoked wave," van der Heijden continues, "but I'm skeptical about the existence of what is customarily termed a cochlear amplifier." His position makes sense, since after 35 years the evidence for amplification is still circumstantial at best, and experts disagree on the basic mechanisms. "Amplification requires phase-locked mechanical feedback to high-frequency input – as high as 100 kHz for bats and dolphins – which is physiologically very implausible." Moreover, he points out, it serves no known purpose: In order to amplify faint sounds, you need to detect them in the first place – so why not stop there if your aim is to hear the sound? "You might think that amplifying faint signals improves their detectability, but that is not the case. Amplifiers always worsen the signal-to-noise ratio."
An alternative to amplification – the one that van der Heijden has taken – is focusing available sound energy. "In a wave this is done by slowing it down, which causes a traffic jam-like congestion of the energy. In addition, from measurements we know that by the time the vibrations are converted to neural signals, the speed of the energy transport has slowed down to a mere walking pace. No amplifier needed!" In fact, in vivo experiments by van der Heijden and his former PhD student Corstiaen Versteegh showed that deceleration is steep, giving sharp peaking. "However," van der Heijden emphasizes, the question now becomes, What is the physics behind the steep wave deceleration?" In the paper, van der Heijden notes that he expects that these new data and ideas will help them to understand the basis of cochlear frequency selectivity and gain control in the near future.
