Foil type modulates developmental changes in statistical learning across childhood to adulthood

Statistical learning (SL) plays a fundamental role in language acquisition, higher-order cognition, and adaptive behavior. While extensive research has demonstrated the importance of SL across different developmental stages, the precise trajectory of SL from childhood to adulthood remains poorly understood. To address this gap, we recruited school-aged children and young adults to complete an auditory SL task. During exposure phase, participants listened to a continuous speech stream composed of trisyllabic nonsense words across three blocks. They then completed a two-alternative forced-choice recognition test and reported their judgment basis. Results revealed children and adults rapidly extracted statistical regularities and segmented words after 4.5 min of exposure. Crucially, within childhood, Grade 5 children outperformed Grades 1 and 3 for nonword foils, whereas performance for partword foils remained relatively stable. From late childhood to adulthood, nonword foils performance became comparable, but adults selectively outperformed children for partword foils. Confidence analyses further revealed an adult advantage in metacognitive sensitivity for nonword foils, suggesting a dissociation in the developmental trajectories of cognitive and metacognitive processes in SL. These findings highlight the critical role of foil type in detecting developmental changes in SL and illustrate the differential maturation of cognitive and metacognitive mechanisms across development.