Bilingual Exposure In The Womb Affects Newborns' Speech Perception

Introduction

It's well established that babies in the womb hear and learn about speech, at least in the third trimester. For example, newborns have been shown to already prefer the voice of their mother, recognize a story that had been repeatedly told to them while in the womb, and tell apart their mother's native language.

Main Digest

What wasn't known until now was how developing fetuses learn about speech when their mother speaks to them in a mix of languages. Yet this is common: there are 3.3 billion bilingual people (43% of the population) worldwide, and in many countries, bilingualism or multilingualism is the norm.

"Here we show that exposure to monolingual or a bilingual speech has different effects at birth on 'neural encoding' of voice pitch and vowel sounds: that is, how information about these aspects of speech has been initially learned by the fetus," said Dr Natàlia Gorina-Careta, a researcher at the Institute of Neurosciences of the University of Barcelona, and the joint first author of a new study in Frontiers in Human Neuroscience.

"At birth, newborns from bilingual mothers appear more sensitive to a wider range of acoustic variation of speech, whereas newborns from monolingual mothers seem to be more selectively tuned to the single language they have been immersed in."

Study Done In Polyglot Catalonia

Gorina-Careta and colleagues did their study in Catalonia, where 12% of the population habitually use both Catalan and Spanish. They recruited the mothers of 131 one- to three-day old newborns (including two pairs of twins) in Sant Joan de Déu Barcelona Children's Hospital as volunteers.

Of these mothers, 41% replied in a questionnaire that they spoke exclusively Catalan (9%) or Spanish (91%) during their pregnancy, including when talking to their growing bump. The other 59% had spoken in two languages (at least 20% of the time for the second language): either Spanish and Catalan or a combination of one of these with languages such as Arabic, English, Romanian, or Portuguese.

"Languages vary in the timing aspects of speech, such as rhythm and accentuation, but also pitch and phonetic information. This means that fetuses from bilingual mothers are expected to be immersed in a more complex acoustic environment that those from monolingual mothers," said Dr Carles Escera, a professor at the same institute and one of the two corresponding authors.

The researchers placed electrodes on the babies' foreheads to measure a particular type of electrophysiological brain response - the 'frequency-following response' (FFR) - to repeated playback of a carefully selected sound stimulus, 250 milliseconds long and composed of four stages: the vowel /o/, a transition, the vowel /a/ at a steady pitch, and /a/ rising in pitch.

/o a/ Sound

"The contrasting vowels /o/ and /a/ belong to the phonetic repertoire of both Spanish and Catalan, which is partly why we chose them," explained joint first author Dr Sonia Arenillas-Alcón from the same institute.

"Low frequency sounds like these vowels are also transmitted through the womb reasonably well, unlike mid- and high- frequency sounds that reach the fetus in a degraded and attenuated manner."

The FFR measures how precisely the action spikes produced by neurons in the auditory cortex and the brainstem mimic the sound wave features of the stimulus. A more distinctive FFR is evidence that the brain has been more effectively trained to pick up precisely that sound. For example, the FFR can be used as a measure of the degree of auditory learning, language experience, and musical training.

The authors showed that the FFR to playback of the /o a/ sound was more distinctive, that is, better defined and with a higher signal-to-noise ratio, in newborns from monolingual mothers than in newborns from bilingual mothers.

Possible Trade-off

These results suggest that the brain of fetuses of monolingual mothers had learned to become maximally sensitive to the pitch of just language. In contrast, the brain of fetuses of bilingual mothers seem to have become sensitive to a wider range of pitch frequencies, but without generating the maximal response to any of them. A trade-off may thus exist between efficiency versus selectivity in learning about pitch.

"Our data show that prenatal language exposure modulates the neural encoding of speech sounds as measured at birth. These results emphasize the importance of prenatal language exposure for the encoding of speech sounds at birth, and provide novel insights into its effects," said Escera.

Joint corresponding author Dr Jordi Costa Faidella, an associate professor at the same institute, cautioned:

"Based on our results, we cannot make any recommendation to multilingual parents. The sensitive period for language acquisition lasts long after birth, and thus postnatal experience may well overshadow the initial changes undertaken in the womb. Future investigation into how a bilingual language environment modulates sound encoding during the first years of life will shed more light into this issue."

Related Information

• Motherese - The Sound of Baby Talk Across Languages: Mothers using motherese or baby talk plays important role in language learning, engaging child emotions and highlighting structure in language to help babies decode syllables and sentences.
• Sounds Help Autistic Kids Develop Speech and Gestures: Doctoral thesis in linguistics shows children with ASD can develop speech, gestures and sense of rhythm and melody by listening to various speech sounds.
• Children and Speech or Language Impairments: A speech or language impairment means an impairment of speech or sound production fluency voice or language.
• Multiple Senses Used in Speech Perception: Recent studies suggest that we use a variety of senses for speech perception including lip reading.
• Famous People Who Have or Had Speech Differences or Stutter: A list of well known and famous people who have or had speech differences including stuttering during their lives.
• Autism Features A Unique Vocal Signature: Vocal analysis technology could change the study of language development as well as screening for autism spectrum disorders.
• Autistic Children Exhibit Three Unique Language Comprehension Profiles: A large study of language comprehension acquisition in children with autism reveals a more complex development process and advocates for new therapy approaches.

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This peer reviewed publication was selected for publishing by the editors of Disabled World due to its significant relevance to the disability community. Originally authored by Frontiers, and published on 2024/05/22 (Edit Update: 2024/06/17), the content may have been edited for style, clarity, or brevity. For further details or clarifications, Frontiers can be contacted at frontiersin.org. NOTE: Disabled World does not provide any warranties or endorsements related to this article.

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