Cochlear mechanisms of frequency and intensity coding. II. Dynamic range and the code for loudness
1Institute for Sensory Research, Syracuse University, NY, USA. monita@hei.org
Hearing Research
|November 21, 1998
Summary
This study reveals how auditory nerve fibers encode sound intensity. Loudness perception relies on the linear growth of inner hair cell responses and response areas, not just excitation at the characteristic place.
Area of Science:
- Auditory Neuroscience
- Sensory Physiology
- Psychoacoustics
Background:
- Previous research detailed sound pressure level (SPL)-dependent transfer function changes in cochlear cells (500-2500 Hz).
- Observed SPL increases caused significant peak shifts and compressive nonlinearity in transfer functions at characteristic frequency (CF).
Purpose of the Study:
- To investigate auditory intensity coding mechanisms in the auditory periphery using existing transfer function data.
- To propose a novel explanation for the differing dynamic ranges of low- and high-threshold auditory neurons.
- To explore alternative excitation patterns for loudness coding beyond excitation growth at the characteristic place.
Main Methods:
- Analysis of previously recorded transfer functions from inner hair cells (IHCs), outer hair cells, and supporting cells in the Mongolian gerbil cochlea.
- Examination of data from the perspective of auditory intensity coding.
- Exploration of excitation pattern candidates for loudness coding.
Main Results:
- Excitation growth at the characteristic place saturates rapidly for pure tones, limiting its capacity for encoding wide dynamic range loudness.
- The growth of the IHC transfer function peak and response area show a linear relationship with loudness growth across a broad dynamic range.
- A new hypothesis is presented for the mechanisms underlying the distinct dynamic ranges of low- and high-threshold auditory neurons.
Conclusions:
- Auditory intensity coding relies on mechanisms beyond simple excitation growth at the characteristic place.
- Linear growth in IHC transfer function peak and response area are key contributors to encoding loudness.
- The findings provide insights into the neural basis of loudness perception and neuronal dynamic range differences.
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