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This study investigates the persistence of phonological traces from a forgotten birth language in international adoptees, using automatic speech recognition models to simulate their experience. The researchers found that these traces remained in the lowest, pre-phonemic layers of the models even after switching to a second language, leading to a 14% faster re-learning of the first language compared to naive models. The findings suggest that critical-period effects are due to entrenched foundational representations rather than a loss of plasticity, highlighting the importance of experience in language acquisition.
Traces of a forgotten language can enhance re-learning speed by 14%, challenging the notion of critical periods as purely maturational.
International adoptees retain phonological traces of a birth language they can no longer speak or comprehend, a persistence typically attributed to a biologically-timed critical period. We asked whether it could instead reflect the ordinary dynamics of learning, using automatic speech recognition models that simulate the international adoptee experience without maturational confounds. Models were trained on one language and then abruptly switched to a second. We found that traces of the first language persisted throughout second-language training, but mainly in the lowest, pre-phonemic layers. These traces were functional, as models with early exposure re-learned their lost first language 14% faster than naive models; this advantage held even against models adopted early from a related language and disappeared when the earliest layers were substituted from a non-adopted model. We argue that these critical-period effects reflect entrenchment of foundational representations rather than a maturational loss of plasticity, and that experience plays a central role in critical periods in language acquisition.
