Consider the place where the actual transformation of the physical sound to a neural signal takes place - the inner ear. It is filled with lymph (salt water). It does not matter through which media the sound travels before, the final media is lymph with a constant relation between frequency and wavelength.

Thanks. So there is no mechanism to encode wavelength as a neural signal independently from frequency? It seems it could happen binaurally at lower frequencies.

Philip, a number of principles are involved here. Under water, sound is not detected through the usual air conduction mechanisms as in the air, so while the pitch should be same no matter how detected, the resonance and timbre factors (ie, hearing the difference between say a trumpet and an oboe playing the same note) will not be discernible to the human ear because the medium of transfer has changed. The only thing that could be heard by humans in the underwater setting would be through the conductive mechanisms. A good review of how sound travels through water can be found at http://www.rjeint.com/acousticTerms.htm. Sound itself as an energy will travel farther through water than air (about 5 times are fast) because of the density of the medium, but the ability of the human ear to detect it in the usual manner is impossible. As you mentioned above, what can be detected, though, will be much more easily detected in the lower frequencies because lower frequencies travel farther in the water medium and also because the mastoid/temple/cochlear bone are more sensitive to low tones than higher tones.

I have no idea. Why not design an experiment to find out?

As an educator also in communicative disorders (my main field is behavioral medicine but have published and worked a great deal in the audiology and hearing health field) I am relatively certain this type of experiment has been replicated numerous times. The outcomes have been that we cannot "hear" through the usual acoustic mechanisms but instead have to depend upon two routes of detection, one conduction through the tactile properties of the temporal bone to the cochlea, and the other would be hydraulic pressure against the tympanic membrane, which then is transfered via mechanical energy through the ossicular chain to the oval window of the cochlea to be transferred back to hydraulic and then neural energy. The proportion of conducted energy would change markedly from the air conduction to hydraulic conduction, plus all of the resonant properties, such as timbre, reverberation, etc. would be absent under water. Now, if the sound was detected by another means and than transferred back into an air conducted environment (such as military personnel use in submarine navigation) many of these properties could be restored or at least detected.

As already mentioned the wavelength is fixed in the ear for any frequency, regardless the wavelength in the surrounding medium. Nevertheless the auditory system does a mechanical frequency analysis in the Cochlea as well as a neuronal period time analysis. For auditory localization it might be interesting to find out whether characteristic modifications of the sound wave (as mentioned by Max) can be directly detected by the neuronal auditory system (e.g. neuronal autocorrelators or neuronal correlators) or are decoded later in the brain.

As said by people already: the medium only has influence on the propagation SPEED, not on the frequency of the source. The number of periods per second is defined by the source. The wavelength is dependent of the medium which follows from the constant frequency: wavelength = propagation speed / f. The sound waves in water activate the eardrums and we hear exact the same frequency as the source produces. An other story is the reverberation in water. Because the prop. speed in water is about 4 times as high as in air, the spatial impression is much smaller than the same space in air. Some people know that if you fill your lungs with helium, your speech will sound as Donald Duck then. That is caused by the fact that the sound SOURCE is altered by the higher prop. speed of helium in your throat and mouth cavities (the vocal tract). In this case the production of the sound is dependent of the gas in the vocal tract: the resonations (formants) depend on the gas present.

Mario, I simply tried to emphasize some terms. Don't know how to do that in a different way with these limited editor. No offense meant.

About the subject: probably sometimes things are not so complicated. From the vibration of the eardrums, exited by the water sound waves, the signal travels exactly in the same way as in the case when the eardrums were exited by the air sound waves. And the frequency of the vibration at the eardrums must be the same as that of the source, independent of the propagation speed, like I said before. That's an answer to the original question I think.

your hear the same pitch (1 kHz) under water or in air (whatever temperature). But - as pointed out by several contributions - the localisation is narrowed due to the higher speed of sound under water. We had a very impressive transmission from a concert hall recording to a swimming pool equipped with underwater loudspeakers. The stereophonic impression was of course reduced. But the excellent reverberation underwater produced an interesting spatial impression.

Excellent points, Volker. While resonant attributes do change, the fundamental remains firmly established in air or water. The native 424 Hz (A) tone (if my memory serves me right) for wolves in the wild, bird songs, and whale songs, is the frequency of nature that communicates through the mediums of air and water undeviated. Quite a marvelous experience to be there and witness the phenomenon.

Just a small correction, Shai. It is when you said: "No matter which type of conduction is active, eventually the cochlea (more specifically, the outer hair cells) is the sensory organ which collects and transform the sound into the auditory system."

In fact, it is the inner hair cells that are responsible for transducing mechanical energy into electrochemical energy in the form of action potentials which travel along the auditory nerve carrying spectro-temporal information about the sound stimulus to the brain. The outer hair cells act as miniature motors that sculpt the form of the traveling wave sharpening its response and thus increasing frequency resolution while amplifying the response (cochlear amplifier). Sorry it took me nearly seven years to respond!

All the best,

Peter

Although pitch perception of a pure tone is strongly correlated with frequency, there are also smaller effects of level—see Brian Moore's "Psychology of Hearing" or any review of pitch perception. As we don't conduct sound to the cochlea as well underwater, we should expect some effects of sound level and their downstream consequences of pitch. Pressure would also likely have an effect on pitch perception; middle ear infections can squeeze the cochlea and affect its function, certainly affecting audibility and probably affecting pitch perception. This could account for the diver's report of sounds changing at depth.