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Intermodulation distortion in the cochlea as shown by offset action potential (AP) masking curves
1Department of Otolaryngology and Communicative Sciences, Medical University of South Carolina, Charleston 29425.
The Journal of the Acoustical Society of America
|March 1, 1990
Summary
The secondary peak in auditory nerve action potential (AP) tuning curves is explained by cochlear intermodulation distortion (IMD). This distortion acts as a masker, influencing neural responses at the probe tone offset.
Area of Science:
- Auditory neuroscience
- Psychoacoustics
- Signal processing in the cochlea
Background:
- Simultaneous masking of auditory nerve action potentials (AP) can yield two tuning curve tips, particularly at probe tone offset.
- The secondary peak, appearing above the probe frequency, was unexplained in prior research by Henry and Lewis.
Discussion:
- The secondary tip is hypothesized to result from intermodulation distortion (IMD) generated within the cochlea.
- Cubic IMD (2f1-f2) from probe-masker interaction acts as a forward masker for the offset response.
Key Insights:
- The lower sideband of frequency splatter at probe offset is identified as the primary stimulus for the evoked neural response.
- This explains why offset tuning curves consistently show a primary tip lower than onset curves.
Outlook:
- Further investigation into IMD as a masker in auditory responses is warranted.
- This mechanism provides a unified explanation for observed phenomena in auditory nerve tuning curves.