A group of young Americans arrived in South Korea for a six-week intensive language course. On weekdays they spent about four hours in Korean-medium classes. Outside class, most still spoke mainly English, and none had significant prior experience with Korean.
Yet when linguist Charles Chang measured their speech week by week, parts of their English were already moving.
The clearest shift appeared in the tiny interval between releasing a consonant and beginning the vibration of the vocal cords. Phoneticians call this interval voice onset time, or VOT. In English words beginning with sounds such as p, t and k, the students’ average VOT became longer during the course, moving in the direction of the Korean sounds they were learning. Smaller, more selective changes also appeared in pitch and vowel measurements.
This sounds like a story about a second language invading the first. It is not. The study had only 19 analyzed learners, used carefully read single-syllable words, began its first measurement after roughly a week of Korean exposure, and included neither a no-Korean comparison group nor a follow-up after the students left. It cannot tell us whether anyone sounded different in conversation, whether a listener would have noticed, or whether the changes lasted.
What it does show is more interesting than the alarming version. An adult’s first-language speech system is not acoustically frozen. Selected features can shift during new language experience. But a changed feature is not the same thing as a lost language.
What does language attrition mean for your accent?
The phrase compresses several different measurements into one familiar idea.
A laboratory can measure an acoustic feature such as VOT in milliseconds. A listener can rate a recording on a scale from “clearly native” to “clearly non-native.” Another listener can judge how easy the speech is to understand. An experiment can test whether a speaker hears two sounds as belonging to different categories. These results may be related, but they are not interchangeable.
That distinction matters because language attrition is not a substance that drains evenly from a bilingual mind. In research, the term covers changes associated with reduced use of, or altered contact with, a language. Researchers may describe some speech patterns more specifically as phonetic or phonological attrition. A study must still specify what changed: access to a word, a grammatical choice, a speech sound, a listener’s rating, or something else. “Language loss” is a much broader phrase than any one of those outcomes, and a changed accent is not a direct measure of overall first-language proficiency.
Chang’s learners therefore give us evidence about selected acoustic features under one short, intensive condition. They do not give us a before-and-after recording of a whole native accent, much less a measurement of English disappearing.
The question most readers have in mind is usually longer-term: after years of living in a second-language environment, can the first one begin to sound foreign?
After years abroad, the result is a distribution—not a rule
Linguist Esther de Leeuw investigated 57 German speakers who had moved as adults to either Canada or the Netherlands. Nineteen trained listeners judged recordings of their German. The ratings did not divide neatly into migrants whose accents had changed and migrants whose accents had not.
Twenty speakers fell in a “clearly native” range. Fourteen fell in a “clearly non-native” range. The remaining 23 occupied an uncertain middle.
That middle is important. It resists the idea that sustained immersion simply flips a native accent into a foreign one. It also warns against turning one sample into a prevalence estimate. The study was observational, and its destination-country contrast was not simple. Later acoustic work used a small, partly overlapping sample and did not map every person’s listener rating directly onto that person’s sound measurements.
Several studies in this sequence come from a connected research network. They use distinct samples and measures in places, but they should not be counted as a stack of fully independent replications.
Other research reinforces the variability. In one study by Holger Hopp and Monika Schmid, 29 of 40 adult bilinguals remained within the monolingual comparison range for perceived foreign accent. Such comparison groups are useful, but they are not timeless accent authorities: region, dialect, age and listener experience can all affect the baseline.
The careful conclusion is not that long-term first-language pronunciation never changes. Some studied speakers received listener ratings outside the comparison range, and some measured features differed. The conclusion is that sustained second-language experience does not produce one inevitable accent outcome.
Part of an accent is in the listener’s ear
A foreign-accent rating can feel like a direct reading of the speaker. It is also a response made by a listener.
In a study by Lisa Kornder and Ineke Mennen, two listener groups judged the same speech from three bilingual speakers differently. The study was small, but the logic is powerful: if the recording stays constant while the rating changes, the rating cannot be a property of the speaker alone. Listeners with greater experience of that kind of bilingual speech gave different ratings; experience was associated with what they judged ordinary or marked.
That does not mean accent ratings are imaginary. A later study led by Ditewig compared listener judgments with particular acoustic patterns and found associations between selected measured features and listener ratings. Its sample—eight bilingual speakers and three controls—was too small to turn those links into a universal map. Still, it helps place the evidence between two bad extremes. Listeners may respond to real acoustic cues, but no rating is a complete diagnostic scan of a person’s language.
Nor does “foreign-accented” mean “hard to understand.” Research by Yazawa and colleagues found that accentedness and comprehensibility could diverge. The study examined first-language Japanese speech in proficient learners of English, but its cross-sectional associations cannot establish within-person attrition or a causal effect of English. Its lesson is nevertheless essential: social judgments of nativeness and practical understanding are different outcomes.
Thirteen days back in Poland
If pronunciation is responsive to experience, returning to a first-language environment might move it again. A 2026 study by Marta Marecka and colleagues tested Polish migrants living in the United Kingdom in two counterbalanced sessions: one after at least a month without a visit to Poland, and another shortly after they returned from a visit averaging 13.6 days.
The researchers focused on one tightly defined contrast: the timing distinction between Polish p and b. After the visit, the migrant group’s production shifted relative to a comparison group that had remained in Poland. The statistical interaction supports change in that production measure under the studied reimmersion condition.
But the rest of the design prevents the tempting headline that “their native accent came back.” A behavioral perception task did not show the corresponding group-by-session interaction. The EEG portion was conducted in a single session, so it could not test reversal over time. The experiment examined read words and one Polish consonant contrast, not a global accent.
The study is valuable precisely because its parts do not collapse into one result. Production shifted in one measure. Behavioral perception did not show the corresponding group-by-session interaction. Neural responses answered a different, single-session question. A first language can be context-sensitive without behaving like a single dial labeled lost at one end and restored at the other.
There is no simple bilingualism tax
If learning and using a second language imposed a general cost on first-language pronunciation, we would expect the measures to move together. Current studies do not show that pattern.
Two connected studies of Arabic–English bilingual speech examined short and long vowels in the same four-group participant project. Some categories were stable. Other measurements produced mixed differences, and one apparent long-vowel effect may partly reflect regional or baseline variation in the comparison groups. These papers are not two independent replications; they are complementary analyses from a shared project. Together, they illustrate why “stronger second language, weaker first language” is too simple.
A 2025 study by Shaktawat makes the same point at an even smaller scale. Among bilingual and bidialectal speakers from one Indian community, cues within voiced stop consonants did not all pattern alike. The population already knew English, the data were cross-sectional, and the speech was read online. Those limits matter. So does the result: even within one segment, different acoustic cues can show different relationships to the language varieties in contact.
Adult bilingual speech is therefore better understood as a responsive system whose components do not always move together. A particular feature can move while another remains stable. A listener can hear a difference without finding the speech less comprehensible. A short-term shift can be real without being permanent. A long-term group difference can be associated with language experience without proving that the second language alone caused it.
What pronunciation cannot tell you about language loss
The public worry behind “Can you lose your native language?” reaches far beyond accent. It may refer to struggling to retrieve a word, feeling less fluent in a professional register, mixing languages, changing a grammatical preference, or feeling that a language no longer fits one’s daily life. A pronunciation study cannot settle all of those questions.
That is not merely a warning about terminology. It is a measurement problem. In a 2025 study of first-language attrition, Zingaretti and colleagues used separate tasks for the lexicon, syntax–pragmatics and prosody. The domains did not become one master score, and the prosodic analysis was exploratory. The study cannot prove that people with accent changes have no changes elsewhere. It shows why each domain requires its own evidence.
A broad review by Gallo and colleagues draws a similar boundary around nonpathological adult first-language attrition. Reduced accessibility or changed processing in some tasks is not the same as clinical language loss, nor is it equivalent to the developmental consequences that can follow when a child is abruptly separated from an early language environment.
This gives us a precise answer to the original question. Learning and using a second language can accompany changes in selected features of an adult’s first-language pronunciation. Some long-term bilingual samples include speakers whom listeners rate as less native-sounding; many speakers and features remain within comparison ranges. Context and listener experience matter. In Marecka’s sample, one read-word measure of the Polish p–b timing contrast shifted toward more Polish-like values after short reimmersion; that result does not generalize to a whole accent.
None of that, by itself, establishes that the first language as a whole is being lost.
Return to the English consonants measured during Chang’s six-week Korean course. Their timing shifted. We still do not know whether anyone heard the shift in ordinary conversation, whether it persisted, whether Korean exposure alone caused it, or what happened to vocabulary, grammar and daily command of English. The measurement is not trivial. It reveals a first-language speech system that remains responsive in adulthood.
The mistake is not noticing that the sound moved. The mistake is asking that one moving sound to tell us the fate of an entire language.
Sources
The list below includes the direct studies, synthesis work and boundary evidence used during the article’s research and verification, including sources that constrained claims rather than supplying a body-text example.
- Chang, C. B. (2012). “Rapid and multifaceted effects of second-language learning on first-language speech production.” Journal of Phonetics. https://doi.org/10.1016/j.wocn.2011.10.007
- de Leeuw, E. (2008). When Your Native Language Sounds Foreign: A Phonetic Investigation into First Language Attrition. Queen Margaret University. https://eresearch.qmu.ac.uk/items/3b7ed3d1-c1b0-4202-8756-e0291c001137
- Hopp, H., & Schmid, M. S. (2013). “Perceived foreign accent in first language attrition and second language acquisition: The impact of age of acquisition and bilingualism.” Applied Psycholinguistics. https://doi.org/10.1017/S0142716411000737
- Kornder, L., & Mennen, I. (2021). “Listeners’ linguistic experience affects the degree of perceived nativeness of first language pronunciation.” Frontiers in Psychology. https://doi.org/10.3389/fpsyg.2021.717615
- Ditewig, S. et al. (online 2024; issue 2025). “The Relation Between Perceived Non-Native Features in the L1 Speech of English Migrants to Austria and Their Phonetic Manifestation in L1 Productions.” International Journal of Bilingualism. https://doi.org/10.1177/13670069231217595
- Yazawa, K. et al. (2024). “More Foreign-Accented but More Comprehensible: Attrition and Amelioration of L1 Speech in Proficient L2 Learners.” F1000Research. https://doi.org/10.12688/f1000research.148193.1
- Marecka, M. et al. (2026). “Can Language Attrition Be Reversed: Evidence From Speech Perception and Production.” Cognition. https://doi.org/10.1016/j.cognition.2026.106571
- Kornder, L., Alharbi, R., & Foltz, A. (online 2025; issue 2026). “First Language Maintenance and Second Language Attainment in Late Bilingual Speech: The Case of Short Vowels.” Language and Speech. https://doi.org/10.1177/00238309251344889
- Alharbi, R., Kornder, L., & Foltz, A. (2026). “Acquisition and Attrition in Bilingual Vowel Systems: Evidence From Arabic and English.” Frontiers in Language Sciences. https://doi.org/10.3389/flang.2025.1738371
- Shaktawat, D. (2025). “Phonetic Attrition Beyond the Segment: Variability in Transfer Effects Across Cues in Voiced Stops.” Languages. https://doi.org/10.3390/languages10110281
- Zingaretti, M. et al. (2025). “L1 Attrition vis-à-vis L2 Acquisition: Lexicon, Syntax–Pragmatics Interface, and Prosody in L1-English L2-Italian Late Bilinguals.” Languages. https://doi.org/10.3390/languages10090224
- Gallo, F. et al. (2021). “First Language Attrition: What It Is, What It Isn’t, and What It Can Be.” Frontiers in Human Neuroscience. https://doi.org/10.3389/fnhum.2021.686388
- Stoehr, A. et al. (2017). “Second Language Attainment and First Language Attrition: The Case of VOT in Immersed Dutch–German Late Bilinguals.” Second Language Research. https://doi.org/10.1177/0267658317704261
- Kartushina, N. et al. (2016). “Mutual Influences Between Native and Non-Native Vowels in Production: Evidence From Short-Term Visual Articulatory Feedback Training.” Journal of Phonetics. https://doi.org/10.1016/j.wocn.2016.05.001
- de Leeuw, E., Schmid, M. S., & Mennen, I. (2010). “The Effects of Contact on Native Language Pronunciation in an L2 Migrant Setting.” Bilingualism: Language and Cognition. https://doi.org/10.1017/S1366728909990289
- de Leeuw, E., & Chang, C. B. (2024). “Phonetic and Phonological L1 Attrition and Drift in Bilingual Speech.” In The Cambridge Handbook of Bilingual Phonetics and Phonology. https://doi.org/10.1017/9781009105767.033
- Shaktawat, D. (2025). “Identity-Driven Variation in Phonetic Backward Transfer: Glaswegian Versus Indian Identity in Glasgow-Indian Bilinguals’ VOT.” Bilingualism: Language and Cognition. https://doi.org/10.1017/S136672892510014X
- Laméris, T., & Kubota, M. (2026). “L1 Phonetic Reversal and L2 Phonetic Attrition in Japanese–English Bilingual Returnee Children Over the Course of Five Years: An Acoustic Study.” Second Language Research. https://doi.org/10.1177/02676583261461940