Loud sounds spread cochlear activation broadly and respond faster than soft sounds

Evidence

The high Q value at low levels of excitation results in considerable activation only near 500 Hz in the 40-dB case. When the SPL of the sinusoid is raised to 90 dB, the activation spreads over a large range towards higher frequencies. This behaviour matches the results shown in Figure 7.11a, where the position on the basilar membrane is sensitive to frequency very selectively only when the excitation level is low, and when the level is increased, it also responds to frequencies lower than its best frequency. Notice also in Figure 7.12 that for the 40-dB case the maximum velocity is obtained after 10 ms of stimulus, whereas in the 90-dB case it is reached at 4 ms. This is a result of the active amplification of the vibration, which takes some time to build up. — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 761

To illustrate this phenomenon more clearly, Figure 7.12 shows the velocity patterns that arise at different positions of the membrane when two 500-Hz sinusoids with levels 40 dB SPL and 90 dB SPL are fed to a non-linear model of the cochlea. The high Q value at low levels of excitation results in considerable activation only near 500 Hz in the 40-dB case. When the SPL of the sinusoid is raised to 90 dB, the activation spreads over a large range towards higher frequencies. This behaviour matches the results shown in Figure 7.11a, where the position on the basilar membrane is sensitive to frequency very selectively only when the excitation level is low, and when the level is increased, it also responds to frequencies lower than its best frequency. Notice also in Figure 7.12 that for the 40-dB case the maximum velocity is obtained after 10 ms of stimulus, whereas in the 90-dB case it is reached at 4 ms. This is a result of the active amplification of the vibration, which takes some time to build up. — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 761

Categorization

• XREF: Wide dynamic-range compression scheme in auditory nerve firing pays off in understanding why loud environments mask quiet detail.
• DEFINE: Active amplification is the cochlea mechanism that elevates low-level responses and takes time to build up.
• corroborated: 4 independent passages support this claim — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 761