Development of the Auditory System from Conception to Term

Found a great article on the Development of the Auditory system from conception to term.  I've attached the article at the bottom of this blog.

Article is by: Robert E. Lasky, PhD, Amber L. Williams

It's pretty detailed, but it gives insight into these areas:

1. Explains when the fetus begins to respond to sound.

2. Describes the type of sounds to which fetuses and extremely preterm newborns initially respond.

3. Explains why the fetus is exposed to low-frequency sounds.

4. Describes the role of the fetal cochlea and the outer and middle ears in response to sound.

5. Compares and contrasts the response to sounds in the fetus of the same postmenstrual age and preterm newborns.

 

Conclusions

Results of investigations of auditory development in fetuses and infants suggest that:


● Prior to 20 weeks GA, the cochlear partition does not seem capable of the sound-induced movements that are later responsible for the transduction of sound into neural impulses.

● The first responses to sound are recorded between 20 and 25 weeks PMA in the fetus.

● By approximately 30 weeks GA, the peripheral auditory system is mature enough that the sensitivity and frequency resolution of auditory function is relatively adultlike. By term, newborn sensitivity and frequency resolution is nearly indistinguishable from the adult.

● Small outer ear canals and immaturities in the middle ear in newborns (particularly small, preterm newborns) emphasize high frequencies and attenuate low frequencies.

● Although the neural pathway to the auditory cortex is functional when the cochlea becomes capable of responding to sound, myelination and synaptogenesis continue postnatally.

● The uterine environment is dominated by low-frequency sounds generated internally and externally. High frequencies are filtered by maternal tissue.

● The mother’s voice is among the more prominent uterine sounds.

● Because fetuses develop in a fluid environment, their outer and middle ears are not prominently involved in hearing.

● Oxygenation is higher and more variable in the pre-term newborn than the fetus. Consequences of increased oxygenation are an increased auditory sensitivity as well as concerns about toxicity to rapidly developing systems.

● Based on few data, nursery policies have shifted to reducing environmental stimulation to preterm newborns more consistent with the fetal experience.

 

The Development of the Auditory System from Conception to Term

October 16, 2014 by Brad Sorock
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