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Dear list,
thank you all for
the many responses. Below I try to sort and summarize the
information:
Reasons why extended (>8 kHz) high-frequency
hearing may be important (besides sound localization!) :
-
Improved perceived music/speech
naturalness: Moore & Tan (2003) showed that reducing the frequency
limit from 16 to 10 kHz also reduced the perceived naturalness of
speech and music.
-
Improved speech perception:
Stelmachowicz, Lewis, Choi, & Hoover (2007) showed that
hearing-impaired children could better distinguish /s/ from /z/ when
the hearing aids were configured to 10 rather than to 5 kHz. On the
other hand, Studebaker and Sherbecoe (1991) showed that in normal
hearing, frequencies above 8 kHz have a rather low importance for
understanding (1% in their speech-importance function measured for
various SNRs). It seems like the speech perception may be a factor -
probably more data are needed here, particularly on specific
syllables...
-
Detection of high-frequency sounds
(like mosquitoes, birds, crickets) especially when masked with a
low-frequency noise (like wind, water). I had a look at an amp.
spectrum of a mosquito sound: most energy was below 4 kHz, and
low-pass-filtering at 8 kHz still resulted in a mosquito sound. I
wonder which environmental sounds with energy above 8 kHz have no or
little energy below 8 kHz - I have no references yet :-(
-
Distance perception, relying on the
frequency-dependent attenuation of sounds. Nice idea - seems like there
are no data available (yet).
-
Better segregation of competing co-located talkers (again, an
idea only, no references available yet)
I also received some further related responses like:
-
We could need high-frequency hearing
because the bandwidth of human speech goes beyond 8 kHz, especially for
consonants. This sounds reasonable, however, I'm not sure if the
hearing bandwidth is automatically related to the voice-production
bandwidth - for some species is seems to be, for the most not...
-
Cochlear amplifier enhances
high-frequency tones more than low-frequency tones. I think that this
may be one of the reasons why we can have high-frequency hearing. On
the other hand, more recent studies suggest strong cochlear
amplification also at lower frequencies...
-
In the middle ear, we have 3
ossicles - having only 1 ossicle (like birds) would be hard to transfer
frequencies beyond 8 kHz without a strong attenuation. This again may
explain why - having some evolutionary pressure - mammals were able to
develop hearing up to 100 kHz.
-
We are interested in extended
high-frequency hearing because it may be good for detecting and
predicting hearing loss - that's interesting!
-
High-frequency hearing allows humans to do amazing things like
echo location (FlashSonar,
you
must see the videos, e.g. here).
So, it's amazing, but the sound localization appears to be the
primary reason for our frequency limit. This is strongly supported by
the correspondence of the head size and the frequency limit for
various mammals (see this link,
thanks to Henry Heffner for the figure+caption), especially
considering the more extended frequency range for echo-locators, and
the strongly reduced frequency range for subterranean mammals.
Also, it seems like the role of speech perception - maybe as
a secondary factor - is unclear yet. If you know some references
about speech perception with frequencies above 8 kHz, I'd really
appreciate that.
Some tertiary factors like sound detection
may have contributed to the development of our hearing range.
Interestingly, hearing the sound probably automatically means
"wanting to know its direction" - and we land at the sound
localization again. If you know some references about the bandwidth
of environmental sounds, especially the contribution of frequencies
above 8 kHz, I'd appreciate them, too.
Thanks,
Piotr
Piotr Majdak wrote:
Dear list,
I'm looking for the reasons for the good high-frequency* hearing in
humans.
The reasons I have until now are actually the obvious ones:
* Pinna localization cues
* Interaural level cues (ILD, they actually start to work from around 2
kHz)
What do you think: if there were no need for the ILD and pinna cues,
would there be any other reasons?
Thanks,
Piotr
*) say, above 8 kHz
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