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Basilar-membrane responses to multicomponent (Schroeder-phase) signals: understanding intensity effects
Van Summers1, Egbert de Boer, Alfred L Nuttall
1Army Audiology & Speech Center, Walter Reed Army Medical Center, Washington, DC 20307-5001, USA.
The Journal of the Acoustical Society of America
|July 26, 2003
Summary
Different Schroeder-phase harmonic complexes elicit distinct basilar membrane (BM) excitation patterns. A linear cochlear model accurately predicts these BM responses, confirming its validity for diverse auditory stimuli.
Area of Science:
- Auditory Neuroscience
- Bioacoustics
- Physiology
Background:
- Harmonic complexes in positive-Schroeder (+Schr) and negative-Schroeder (-Schr) phase share spectral content but differ in basilar membrane (BM) excitation.
- Previous studies indicated more modulated BM excitation for +Schr stimuli compared to -Schr stimuli.
Purpose of the Study:
- To investigate and quantitatively predict localized BM responses to +Schr and -Schr harmonic complexes in the guinea-pig cochlea.
- To validate a linearized cochlear model's ability to predict responses to stimuli with distinct waveform envelopes.
Main Methods:
- Laser velocimetry was employed to measure BM vibrations at a 17 kHz characteristic frequency in guinea pigs.
- Stimuli consisted of +Schr and -Schr harmonic complexes (203 Hz fundamental, 101 components).
- Responses were predicted using a linearized cochlear model based on an indirect impulse response.
Main Results:
- At 35 dB SPL, +Schr complexes induced greater amplitude modulation in BM responses than -Schr complexes.
- Internal modulation decreased for both stimulus types with increasing sound pressure level (SPL).
- The linearized cochlear model accurately predicted observed BM response waveforms when stimulus level matched the model's input level.
Conclusions:
- The findings confirm the validity of the linearized cochlear model for predicting BM responses to diverse stimuli, including those with different phase characteristics.
- The study supports the explanation of cochlear filtering mechanisms within a linear system framework.
- Accurate prediction relies on matching the stimulus level to the model's calibrated input.