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Intensity-invariance of fine time structure in basilar-membrane click responses: implications for cochlear mechanics
1Eaton-Peabody Laboratory of Auditory Physiology, Massachusetts Eye and Ear Infirmary, Boston 02114, USA. shera@epl.meei.harvard.edu
The Journal of the Acoustical Society of America
|August 18, 2001
Summary
The fine time structure of auditory responses remains remarkably consistent across a wide range of sound intensities. This near-invariance suggests cochlear resonant frequencies are largely independent of intensity, challenging conventional cochlear models.
Area of Science:
- Auditory Neuroscience
- Cochlear Mechanics
- Bioacoustics
Background:
- Auditory nerve and basilar-membrane responses to acoustic stimuli exhibit a consistent fine time structure across varying intensities.
- Understanding the origin of this intensity-invariance is crucial for comprehending cochlear mechanics and auditory processing.
Purpose of the Study:
- To explore the origin and implications of the near-invariance of auditory response fine time structure with stimulus intensity.
- To investigate how this symmetry relates to cochlear mechanics and the role of active force generators.
Main Methods:
- Applied the EQ-NL theorem to a family of linear cochlear models with intensity-dependent active force generators (parameter gamma).
- Conjectured that intensity-invariance implies stable pole locations for cochlear partition admittance.
- Computed model responses using an extended squirrel monkey model with different intensity-dependent admittance forms.
Main Results:
- Model responses supported the conjecture that local resonant frequencies of the cochlear partition are nearly intensity-independent.
- Intensity-invariance of resonant frequencies aligns with the observed half-octave shift in basilar-membrane frequency response.
- Best frequency shifts are attributed to global changes in driving pressure, not local resonant frequency alterations.
Conclusions:
- The near-invariance of fine time structure strongly constrains the mechanical influence of outer hair cell (OHC) force generation.
- OHC feedback forces appear not to significantly alter the natural resonant frequencies of the cochlear partition.
- These findings contradict many current cochlear models where OHC forces substantially modify partition reactance and resonant frequencies.
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