My posting sent yesterday, involving the cochlear amplifier (CA), was based on a misunderstanding. I tried to describe the biophysical cause of good high-frequency hearing, not its evolutionary advantage. Nevertheless, one cochlear-mechanics effect may be relevant: If the CA would amplify low-frequency tones by 40 dB, then the basilar-membrane displacement amplitude would be so large (even at fairly low sound-pressure levels) that the organ of Corti would be damaged.
Dr. phil. nat.,
Datum: 25.01.2011 21:24
Betreff: Re: High-frequency hearing in humans
Isn't it parsimonious to assume that humans--and other creatures--have
high frequency hearing for the simple reason that there is lots of
useful information out there in the natural environment in the higher
frequency range? Yes it's also useful for localization etc., but
identifying a source would be at least as critical.
Many critters that we might want to eat, run away from, or merely be
aware of make noises in that range with their vocal tracts, wings, legs
etc (birds, crickets, etc); and others who are bigger still might at
least make HF noise by stepping on leaves/branches etc and hence leave
tell-tale cues in high frequencies. Plus lower frequencies might
occasionally be masked by noise (water, wind...) so one would want to
detect the presence of others even in a noisy environment.
So it would be adaptive to be able to hear them, would it not? That
seems like the simplest explanation to me.
Robert J. Zatorre, Ph.D.
Montreal Neurological Institute
3801 University St.
Montreal, QC Canada H3A 2B4
web site: www.zlab.mcgill.ca