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Auditory evoked potentials to continuous amplitude-modulated sounds: can they be described by linear models?
Electroencephalography and Clinical Neurophysiology
|January 1, 1987
Summary
This study investigated cochlear responses to amplitude-modulated sound, finding that non-linearities increase with intensity. These non-linearities, primarily even-order, may stem from unequal responses to loudness changes.
Area of Science:
- Auditory Neuroscience
- Bioacoustics
- Signal Processing
Background:
- The cochlea processes complex auditory signals, but the precise nature of non-linearities in its responses remains incompletely understood.
- Amplitude modulation (AM) is a key feature of natural sounds, and understanding cochlear processing of AM signals is crucial.
Purpose of the Study:
- To characterize the non-linearities in the auditory nerve's response to amplitude-modulated sounds.
- To determine the order and intensity dependence of these non-linearities.
Main Methods:
- Recorded responses from the cochlear nucleus and round window to pseudorandom noise-modulated tones.
- Utilized cross-correlation and linear modeling to quantify response non-linearities.
- Employed inverse-repeat noise to isolate even-order non-linearities.
Main Results:
- Root mean square (RMS) response values peaked at 40-60 dB above threshold before decreasing.
- The non-linear component of the response increased monotonically with sound intensity up to 60-70 dB above threshold.
- Canceling even-order non-linearities improved agreement between physiological and model responses, suggesting dominance of even-order effects.
Conclusions:
- Auditory nerve responses to AM stimuli exhibit significant non-linearities, predominantly of even order.
- These non-linearities are intensity-dependent and may arise from asymmetric processing of sound level increases and decreases.