Editing Second-language acquisition (section)

== Comparisons with first-language acquisition ==
Adults who learn a second language differ from children [[Language acquisition|learning their first language]] in at least three ways: children are still developing their brains whereas adults have mature minds, and adults have at least a first language that orients their thinking and speaking. Although some adult second-language learners reach very high levels of proficiency, pronunciation tends to be non-native. This lack of native pronunciation in adult learners is explained by the [[critical period hypothesis]]. When a learner's speech plateaus, it is known as [[Fossilization (linguistics)|fossilization]].

Also, when people learn a second language, the way they speak their first language changes in subtle ways. These changes can be with any aspect of language, from pronunciation and syntax to the gestures the learner makes and the language features they tend to notice.{{sfn|Cook|2008|p=232}} For example, French speakers who spoke English as a second language pronounced the /t/ sound in French differently from monolingual French speakers.{{sfn|Flege|1987}} This kind of change in pronunciation has been found even at the onset of second-language acquisition; for example, English speakers pronounced the English /p t k/ sounds, as well as English vowels, differently after they began to learn Korean.{{sfn|Chang|2012}} These effects of the second language on the first led [[Vivian Cook (academic)|Vivian Cook]] to propose the idea of [[multi-competence]], which sees the different languages a person speaks not as separate systems, but as related systems in their mind.{{sfn|Cook|2008|p=15}} A 2025 study found that adult learners can attune to the prosody of a new language after brief exposure, but that concurrent exposure to orthography—especially deep or unfamiliar scripts—hampers this ability. This suggests that difficulties with second-language prosody may be influenced by learning conditions, not just age-related factors.<ref>{{Cite journal |last=Chládková |first=Kateřina |last2=Podlipský |first2=Václav Jonáš |last3=Jarůšková |first3=Lucie |last4=Šimáčková |first4=Šárka |date=2025-02-04 |title=Tuning in to the prosody of a novel language is easier without orthography |url=https://www.cambridge.org/core/journals/bilingualism-language-and-cognition/article/tuning-in-to-the-prosody-of-a-novel-language-is-easier-without-orthography/5A46BC3A2F5EF223322144EE508541A5 |journal=Bilingualism: Language and Cognition |language=en |pages=1–10 |doi=10.1017/S1366728925000082 |issn=1366-7289|url-access=subscription }}</ref>