Fetal Awakenings

Here is the cochlea of a 5-month-old fetus

It is fully developed by this age.  A month later it will be fully functioning. 

Hearing develops after the chemical and tactile senses. They all develop gradually, and I wonder what that must be like. Maybe like very very slowly waking from sleep – that period when our faculties are coming online. 

Nobody knows if fetuses dream, but they do spend most of their time in REM sleep. Even if they do dream, their dreams couldn’t be much different from their “wakeful” period because their experiences are narrowly limited. 

But they can hear during the 3rd trimester. How we know is from work by scientists who monitored the heart rate of fetuses while presenting sounds and saw that the heart rates changed in response to the sounds. Cool!

This is a sheep

Scientists placed recoding devices in the uteruses of sheep to estimate what kind of sound reaches the human fetuses. Apparently certain parts of our anatomy are comparable to sheep’s. 

What they hear are sounds that are muffled kind of like the speech of the grown ups on the Charlie Brown cartoons. Not enough to hear consonants but enough to differentiate some vowels and hear the intonation and rhythm of the speech. 

So as they wake from their fetal sleep into their newborn state, infants already have some familiarity with the musical qualities of language. 

Here’s how scientists have shown that. They hook up newborns to the high-amplitude sucking procedure.

They monitored sucking rate and found that infants’ arousal (measured by sucking rate) increased in response to their mother speaking versus another woman and to their mother’s language (or a rhythmically similar one) versus another language (if it’s rhythmically dissimilar). And the preference was seen even when presenting them with a Charlie Brown-like muffled version of the speech.

Newborns even showed preferences for specific nursery rhymes they heard in utero. I don’t know if there would be any reason to teach my fetal son Goodnight Moon right now, but it’s interesting to know that I could.


References:

Birnholz, J. C., & Benacerraf, B. B. (1983). The development of human fetal hearing. Science, 222, 516–518.

DeCasper, A. J., & Fifer, W. P. (1980). Of human bonding: Newborns prefer their mothers’ voices. Science, 208, 1174–1176.

DeCasper, A. J., & Spence, M. J. (1986). Prenatal maternal speech influences newborns’ perception of speech sounds. Infant Behavior and Development, 9, 133–150.

Griffiths SK, Brown WS, Gerhardt KJ, Abrams RM, et al. The perception of speech sounds recorded within the uterus of a pregnant sheep. J Acoust Soc Am 1994; 96: 2055–63.

Lecanuet, J. P., Gautheron, B., Locatelli, A., Schaal, B.,Jacquet, A. Y., & Busnel, M. C. (1998). What sounds reach fetuses: Biological and nonbiological modeling of the transmission of pure tones. Developmental Psychobiology, 33(3), 203–219.

Mehler, J., Jusczyk, P., Lambertz, G., Halsted, N., Bertoncini, J., & Amiel-Tison, C. (1988). A precursor of language acquisition in young infants. Cognition, 29(2), 143–178.

Nazzi, T., Bertoncini, J., & Mehler, J. (1998). Language discrimination by newborns: Toward an understanding of the role of rhythm. Journal of Experimental Psychology: Human Perception and Performance, 24(3), 756–766.