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<Paper uid="H91-1039">
  <Title>ANALOG IMPLEMENTATIONS OF AUDITORY MODELS</Title>
  <Section position="3" start_page="0" end_page="0" type="intro">
    <SectionTitle>
INTRODUCTION
</SectionTitle>
    <Paragraph position="0"> The &amp;quot;Analog Electronic Cochlea&amp;quot; of Lyon and Mead \[1\] has been presented as a very efficient way to implement a cochlear model in silicon. It was shown to provide some of the basic filtering properties and adaptability potential needed for a comprehensive auditory model. However, we were not able to tune the filters to give a pseudoresonant gain peak greater than about 20 dB, due to poorly understood circuit misbehaviors.</Paragraph>
    <Paragraph position="1"> In the hydrodynamic model on which our cascade filterbank model of the cochlea is based \[2\], the signals in the filter cascade correspond to either pressure (across the basilar membrane) or velocity potential at the membrane (the spatial derivative of velocity potential is the fluid velocity vector).</Paragraph>
    <Paragraph position="2"> For the case of a passive cochlea, the respone of the filters should be monotonically decreasing with frequency; i.e., lowpass. But for a healthy active cochlea in a quiet environment, the active outer hair cells should provide enough gain to change the overall lowpass response to a pseudoresonant bandpass-like response with a broad gain peak of perhaps as much as 60 dB. Over a wide range of sound loudnesses, the filterbank gain should gradually transition between these extremes, acting as an automatic gain control to compress the dynamic range of signals at the output. We have previously discussed the evidence for this kind of function in fact occuring at the mechanical level \[3\]. We are now making progress on getting this behavior into our circuits.</Paragraph>
  </Section>
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