From: Piotr Majdak [mailto:piotr@xxxxxxxxxx]
Sent: Wednesday, February 2, 2011 11:14 AM
Subject: Re: High-frequency hearing in humans
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!
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.Piotr
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.
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?
*) say, above 8 kHz