Language development is a topic that fascinates me for years and
it all started by observing my oldest daughter slowly responding and
developing her linguistic skills by interacting with the outside world.
Making funny but understandable errors, learning by trial and
error…Now when there is a small baby growing in my belly, which
response to touches and voices, I wonder how much it actually hears and
how much what it hears affects its future development…
of the people and research focuses on the brain of the newborn and the
language acquisition after the birth, but brain areas corresponding to
the language development appear in the brain already during the 30th
week of pregnancy, and as soon as from the 18th week of pregnancy, it
can ‘hear’ sounds of your body such as your heartbeat and since the 27th
week auditory learning becomes possible…There are studies that show
that a fetus in the womb reacts to the mother’s voice, to the music,
etc. There are also studies that show that when the baby is exposed to
one language during pregnancy and adopted at birth, it can afterward
still produce mother language sounds or distinguish some words from that
language. All these findings are impressive and bring up an interesting
question – how is the prenatal exposure to sounds and languages
affecting the later development of the language for the baby? Can we
improve kids’ linguistic or musical skills by prenatal exposure to
foreign languages, by talking to them or playing music to them? Or is
how much we talk to the kid affecting our bonding and connection to the
baby? Maybe we cannot answer these questions or not all of them, but we
can see a bit more, what is happening in the womb, we can explore the
life in the darkness and see how the small brain is a step by step
developing and responding to the outer world…
Neurophysiology of the fetus
First, let’s see, what happens with
the baby brain which enables it to hear and recognize the language, all
of which later leads to the fact that newborns might be soothed by
familiar sounds like an adult heartbeat or that they prefer mother’s
language to other languages…. The onset of hearing in humans is around 27 weeks of gestational age , but already since 18th or 19th week, the baby can respond to sounds of the body such as heartbeat or stomach rumbling 
as the human cochlea starts to be slowly functioning . That is the
time when external auditory inputs start to have an effect on the
reorganization of the auditory cortex . To test the onset of hearing,
 performed an experiment, where they exposed the fetus to pure auditory stimuli of different frequencies (100, 250, 500, 1000, and 3000 Hz) –
from 19 to 35 weeks of gestational age (GA). Measuring the responses by
loudspeaker on maternal abdomen and by ultrasound, they observed first
responses for 500 Hz at 19 weeks of GA, then responses to lower
frequencies appeared (At 27 weeks, 96% fetuses were responding to 250
and 500 Hz) and the latest ones were responses to higher frequencies
(responses to 1000 and 3000 Hz haven’t been observed till 33 and 35
weeks, respectively). As the baby brain matures, a big decrease (20-30 dB) in the intensity level required to elicit a response was
observed. This corresponds to the neurophysiological maturation of the
inner ear, which seems to be matured at the end of the 8th month when
all relevant neuronal synapses take their place .
In the 30th week, brain areas corresponding to language development are
developing ([5, 6]). As you maybe know, there is observed a left
hemisphere dominance for language processing, which seems to be
genetically given and we can observe asymmetric development of the brain already before birth.
For example, the temporal plane layer in the left hemisphere is larger
than in the right one. We can also observe that the left hemisphere has
different sensitiveness for speech already from birth (response was
measured by electrical activity – event-related potentials, Mehler).
Interestingly, the development of cortical regions that are connected to
language is slower in the left hemisphere than in the right one (e.g.,
right temporal plane develops at the 30th week of GA, but left one 7-10
days later) ([7, 5]). The fact that brain regions for language
development are distinct already at birth might be a partial
verification for Chomsky  hypothesis, that there exists a universal
innate grammar, which we just fill in with vocabulary and rules.
This above-mentioned development leads to the fact that after 32 weeks of gestation age, the baby may start recognize vowel sounds
from your language , which further leads to the findings which we
will mention later, that the newborn prefers the native language to
other languages .
Sound and music in the womb – is the baby partying there?
we measure what the baby actually hears? It is easy. You can just place
a microphone or hydrophone inside the vagina close to the baby’s head
You will hear a lot of background noise, body noise and mainly low frequencies around 500-700 Hz, all of which are highly attenuated
[10, 11, 12]. Nevertheless, mother voice and external speech will still
be clearly emerging above the background noise with well preserved
prosodic characteristics. [11, 12] found out that even some
phonemes/words are still recognizable (up to 30%). All these speech
connected sounds are quite silent as they are attenuated significantly.
Although you can hear all (close by) external speech, you will get
during your life in the womb most familiar with the mother’s voice,
because there is significantly better transmission of maternal voice
than of external voices – Querleu found out that there is 20dB attenuation of external voices and only 8 dB of mother voices
. How can this be explained? It seems that there are 2 pathways
transmitting the voice – one is the same for both maternal and external
speech, but the mother’s voice is transmitted also through body tissues
and bones which enables kids to get more used to this voice.
This is closely connected to the findings on the newborns, that mother’s voice has calming effects for < 2-week old kids and is more attractive for the newborn than other female voices. On the contrary, newborns do not show any preference for the voice of the father compared to other male’s voices,
even after 4-10 hours of exposure to the father’s voice after
delivery. [10a] Spence  went even further and found out that infants
prefer the maternal low-pass filtered voice, but not the maternal
What is another interesting finding is
that external auditory stimuli in general increases motor responses
(both long term and startle responses) as well as heart rate responses
, but the mother speech can decrease fetal heart rate – the most when the speech is in low frequencies and around 70dB. The responses of the fetus were
measured for tones, vibratory frequency noises, or EAL stimulations
during quiet and active sleep and during active and quiet wakefulness of
the baby – it has been found that although to tones the baby starts to
respond at 27-28th week of GA, to EAL stimuli motor responses appear
already in the 24th week . Bigger responses can be observed during
wakefulness than during sleep. Unborn babies might even start to cry if exposed to a sudden loud noise.
And how is it with the music? Feijoo  measured kids at delivery and 4-5 days old and found out that kids were soothed by the music which their mother listened regularly during last 3 months of the pregnancy way more than any other music.
Postnatal effects of prenatal stimuli
So you can see that it has
been found out, that familiar sounds might soothe crying newborn ,
including adult heartbeat, mother’s voice[13, 10], music , or soap
opera theme .
Question is, how can we find out what a newborn actually prefers? There is an experiment called the non-nutritive sucking behavior of
the newborn which is supposed to measure babies’ responses to
individual stimuli. What should this mean? It is easy, this technical
term hides an easy thing – behavior while sucking on a pacifier.
So basically we measure how much the baby is sucking, what are the
pauses between sucking and frequency of sucking. So easy :).
this method, it has been found that newborn babies exposed to the adult
heartbeat (72 beats/s) were sleeping earlier and gained weight quicker
. Also, intrauterine background noise had a short term pacifying
effect ([10a], Murooka ). Familiar stimuli were also preferred by a
child in selection tasks.
Back to mother’s
voice…DeCasper  found out that 2-3 days old babies preferred a
story that mother read 6 weeks prior to pregnancy to the one they never
heard. And have you ever heard about fetal ‘soap’ addiction? It
was described by Hepper in 1988 , . What they found out? That
there were mothers who regularly watched a soap opera ‘Neighbors’ during
the last weeks of pregnancy (some even twice a day). Maybe you can
already guess what they observed for these babies after delivery. A
crying baby who was ‘listening’ to the soap opera already in the womb,
is more likely to stop crying when the program begins than the baby of a
mother who was not watching it in her pregnancy.
So far I was mainly speaking about voice and sounds, but what about the actual languages? Moon [9a], measured 40 infants about 30 hours old in the nursery using the test for sucking behavior when listening to vowels from native and unfamiliar language.
They found out that babies were sucking longer for the foreign language
than for the native tongue (independent on time since birth, 7-75h),
which indicates that they can differentiate between these two languages
and it seems that the ambient language to which fetuses are exposed in
the womb affects their perception of the native language at phonetic
level. In another study, Moon et al.  measured 2 day old kids of
French and Russian mothers while the same bilingual woman was talking to
them. These kids again preferred the mother’s tongue to the unfamiliar
one and the same behavior was observed also for low-pass filtered
versions, which kept only the prosodic cues of the languages. On top
when they measured kids from families speaking neither French nor
Russian, they were not able to discriminate between these 2 languages.
Maybe you might be a bit skeptical about this
sucking behavior test…Then there is another study conducted by May et
al. , who measured a neural activity of the brain using NIRS (near-infrared
spectroscopy) study on 20 monolingual English 0-3 days old neonates.
She let them be exposed to low-pass filtered sentences of forward
English (familiar language), forward Tagalog (unfamiliar language), and
backward English and Tagalog (non-language) and measured neural
activation by NIRS. They found out bilateral (in both hemispheres)
activation connected to the familiarity of the language and observed
different activation for Tagalog (unfamiliar language). This indicates
that exposure to the language in uterus influences the brain responses of the baby to the native language after birth.
So it actually seems that babies in the womb really listen to us as soon as their hearing enables them so,
although what comes to them is highly attenuated and filtered for high
frequencies. After several months of this auditory experience, they
become attracted to the familiar sounds and patterns of the native language(s).
But it is possible that they actually learn even more from their
prenatal experience as they might become familiar with the prosody of
the languages heard in utero (‘prenatal prosodic bootstrapping’), which
might be crucial for later language acquisition . To conclude, we
can see that long-term premature exposure to auditory (or other sensory
stimuli) in utero might lead to both prenatal and postnatal responses to
And one last thing to mention, the
auditory and language system as a whole continues, of course, to develop
also after a birth – e.g., hearing develops for another 5-6 months
after birth and language areas keep developing for years, so it needs
continuous stimulation through speech, music, and other sounds,
otherwise we might miss the important times (so-called sensible periods)
for its development which might lead to its underdevelopment, as
observed for linguistically or socially deprived ‘wild kids’…but that
is a topic for some other time…
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