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Re: prenatal auditory localization PS

In fact, the wavelength, which equals propagation velocity over
frequency, will be longer than in air (because of the greater speed of
sound in water). Together with the small head size of the fetus this
should lead to extremely small interaural level differences. These two
effects also reduce interaural phase differences, or interaural
time-of-arrival. So it would seems that horizontal localization cues are
very very small for the fetus and from that point of view I would think
it unlikely that even approximate sound localization is possible.

If the fetus is somehow aware of sound location at all, sounds would
probably appear as coming from (nearly) directly ahead, given that
interaural differences are so small. This is assuming the fetus' brain
is already wired for sound localization in air.


Bob Masta wrote:

Another factor to consider is that the prenatal environment is
amniotic fluid, not air.  So presumably all the wavelengths
will be greatly shortened.  I'm not sure how this will affect
shadowing issues, but it would certainly affect phase issues.
Also, since the external sound must go through a tissue
interface before it even gets to the fluid, I'd guess that the
result would be a loss of localization information just from
that... sort of like a big piston driving a small hydraulic

Just my initial off-the-cuff 2 cents' worth.  With more thought
I might get up to 2 bits!

Best regards,

Bob Masta

Erik Larsen                             voice: 617-573-4120
Eaton-Peabody Laboratory                cell : 617-803-6433
243 Charles St, Boston, MA 02114        email: elarsen@mit.edu