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Irreversible specialization for speech perception in early international adoptees compensated by inhibitory control in adulthood
Stockholm University, Faculty of Humanities, Department of Swedish Language and Multilingualism, Centre for Research on Bilingualism.ORCID iD: 0000-0001-7915-6777
Stockholm University, Faculty of Humanities, Department of Swedish Language and Multilingualism, Centre for Research on Bilingualism.ORCID iD: 0000-0001-5203-9175
2022 (English)In: Cerebral Cortex, ISSN 1047-3211, E-ISSN 1460-2199, Vol. 32, no 17, p. 3777-3785Article in journal (Refereed) Published
Abstract [en]

In early childhood, the human brain goes through a period of tuning to native speech sounds but retains remarkable flexibility, allowing the learning of new languages throughout life. However, little is known about the stability over time of early neural specialization for speech and its influence on the formation of novel language representations. Here, we provide evidence that early international adoptees, who lose contact with their native language environment after adoption, retain enhanced sensitivity to a native lexical tone contrast more than 15 years after being adopted to Sweden from China, in the absence of any pretest familiarization with the stimuli. Changes in oscillatory brain activity showed how adoptees resort to inhibiting the processing of defunct phonological representations, rather than forgetting or replacing them with new ones. Furthermore, neurophysiological responses to native and nonnative contrasts were not negatively correlated, suggesting that native language retention does not interfere with the acquisition of adoptive phonology acquisition. These results suggest that early language experience provides strikingly resilient specialization for speech which is compensated for through inhibitory control mechanisms as learning conditions change later in life.

Place, publisher, year, edition, pages
2022. Vol. 32, no 17, p. 3777-3785
Keywords [en]
critical period, event-related brain potentials, international adoption, language acquisition, mismatch negativity
National Category
Neurosciences General Language Studies and Linguistics
Identifiers
URN: urn:nbn:se:su:diva-186208DOI: 10.1093/cercor/bhab447OAI: oai:DiVA.org:su-186208DiVA, id: diva2:1481892
Available from: 2020-10-27 Created: 2020-10-27 Last updated: 2023-11-23Bibliographically approved
In thesis
1. Age and Constraints on Language Learning: First Language Retention and Second Language Acquisition in International Adoptees
Open this publication in new window or tab >>Age and Constraints on Language Learning: First Language Retention and Second Language Acquisition in International Adoptees
2020 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis investigates the influence of age of acquisition on the long-term second language development of international adoptees. Because age of acquisition typically coincides with the onset of bilingualism, the study of maturational age effects in second language acquisition has been empirically and conceptually entangled with changes in language input and use. For international adoptees, however, because the adoptive language is acquired under similar linguistic conditions as non-adopted peers – albeit at a later age of acquisition – questions of age and second language acquisition can be investigated without confounding influences of bilingualism. Study I presents the theoretical argument that, because of the delay in acquisition, the language development of international adoptees should be regarded as a special case of second language acquisition. Furthermore, consistent with the contemporary study of second language acquisition, the effects of this delay should be investigated through ultimate attainment observed in adults. Study II shows that adults in Sweden who had been adopted from Spanish-speaking countries, and Spanish-Swedish bilinguals with the same age of acquisition (3-8 years), have greater difficulty in perceiving Swedish vowel distinctions that do not exist in Spanish compared to native Swedish speakers. This suggests that age of acquisition is a decisive factor for speech perception in a second language. In Study III, Chinese-Swedish adoptees are found to deviate from native Swedish speakers in their production of Swedish vowels that are phonologically identical in Chinese, but not in vowels that are distinctive in both languages. While these results are consistent with predictions based on assumptions of transfer and interference in bilingual speakers, they cannot be explained based on these premises. Instead, the results suggest that early language-specific experiences will affect the pronunciation of vowels in the second language regardless of whether the native language is in use or not. In Study IV, the neural underpinnings of the behavioral results are investigated electrophysiologically, using EEG. This study shows that adult adoptees retain increased neural sensitivity to a native Chinese lexical tone contrast without any exposure to the language for over 15 years. This is reflected in a fast neural response stemming from the auditory cortex and is indexed by the mismatch negativity event-related potential. This suggests that native language sensitivity is not only retained, but is continuously involved in the moment-to-moment processing of speech sounds. Neural oscillations furthermore reveal the involvement of inhibitory processes to attenuate this sensitivity. Finally, positive correlations between neural responses to the native and the adoptive language show that native language retention is not in itself an impediment for second language acquisition. The results from these three studies show how language-specific experiences lead to irreversible specialization in the brain, which will affect the long-term acquisition of a second language. This finding invites a re-evaluation of the hypothesis of a critical period for second language acquisition, based on the notions of probabilistic epigenesis and flexible behavioral adaptation following experience-based functional neural reorganization in early childhood.

Place, publisher, year, edition, pages
Stockholm: Centre for Research on Bilingualism, Stockholm University, 2020. p. 60
Series
Dissertations in Bilingualism, ISSN 1400-5921 ; 31
Keywords
bilingualism, critical period, electroencephalography, event-related potentials, first language retention, international adoption, phonology, second language acquisition
National Category
General Language Studies and Linguistics Neurosciences
Research subject
Bilingualism
Identifiers
urn:nbn:se:su:diva-186210 (URN)978-91-7911-346-9 (ISBN)978-91-7911-347-6 (ISBN)
Public defence
2020-12-14, Online via Zoom, public link is available at the department website, Stockholm, 15:00 (English)
Opponent
Supervisors
Available from: 2020-11-19 Created: 2020-10-28 Last updated: 2022-02-25Bibliographically approved

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Norrman, GunnarBylund, Emanuel

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