Infants and the vowel u

In an online version of the journal Pediatrics (https://pediatrics.aappublications.org) for April 15, 2013, more evidence was found that the sound of music could be beneficial for newborns.  It was found that premature babies in the neonatal intensive care unit (NICU) who had respiratory difficulties did slightly better when presented with recorded sounds of what their mother’s voice would have sounded like in the womb.  Similar findings were found whenever the mother or father sang to them.  The heart rate of these infants slowed by 2-3 beats a minute while listening to these sounds.

Specifically, from data acquired at 11 NICUs that had music therapists employed, for 272 premature infants, over a two-week period, a number of vital signs were recorded.  It turns out that the reduction in heart rate was the same whether the low-frequency sound was provided by a music therapist’s device or by the voice of the parents.

This is more evidence that music (singing) can be beneficial for even our youngest members of society.  For years, parents have been told to talk to their unborn and newborn children in hopes of developing early bonds.

This is a wonderful opportunity to do some math!  Between the outside environment and the hearing mechanism of the fetus lies a pool of amniotic fluid.  As we know from the study of the ear- specifically why we have a middle ear- about 30 dB of sound energy is lost when traversing the boundary between air and fluid.  Here is the math part:

If 99.9% of the sound energy is lost at the air-fluid boundary, this equates to 10^-3, which is one part in 1000.  Converting this to decibels, we have 10log(10^-3), which is -30log10, = -30 dB.  All sounds are quieter by about 30 dB when traversing this boundary.  This is why it’s fine to talk to your friends while fishing- your voice will lose 30 dB of its sound energy en route to the fish.  And since the water is a very noisy place, even the fish with the best hearing will not be able to hear your voice due to all of the environmental masking.

This calculation makes some assumptions such as this 30 dB attenuation is valid for all frequencies as well as the lack of mechanical resonances in the fluid.  These factors may mitigate the 30 dB attenuation figure, but I suspect not by very much, at least for the lower frequency region.  There may be a differing amount of attenuation for the higher frequency region.

Also, neonatal care experts have suggested for years that parents utter the sounds [u] as in ‘boot” to the newborns to facilitate bonding, and perhaps reduce heart rate.  This suggests that neonatal specialists know something about speech acoustics.

The back vowels ([u, o, a]) all have one property in common- they have relatively low frequency second formants (and also low first formants).  The frequencies of the first and second formants for [u] are both very low.  In fact [u] has the lowest first and second formant of any sound in the languages of the world.  So, neonatal care experts obviously understood that a proliferation of low frequency energy would be soothing.

It is not known why sounds that are in the middle of the piano keyboard (around middle C and an octave above) are the ones that are found to be more soothing.  Could it be that these were the sounds that were getting through the amniotic fluid to the fetus’ hearing mechanism?  Clearly more research is required, but it’s gratifying that neonatal care specialists learn so much about speech acoustics in their clinical training.