Bilingualism and cognition: The impact of age of acquisition, language use, and proficiency in cognitively unimpaired older adults

Background: The positive effect of bilingualism as a cognitive reserve factor in aging remains inconclusive, with inconsistencies often stemming from treating bilingualism as a dichotomous variable rather than a dynamic, multidimensional experience.

Objective: To investigate the impact of bilingualism on cognition in cognitively unimpaired older adults, focusing on age of language acquisition (AoA), proficiency, and usage throughout life.

Methods: Data from 2415 participants (aged 45-74) from the Alzheimer's and Families (ALFA) study were analyzed. Cognitive assessments included the Mini-Mental State Examination to assess global cognition, semantic verbal fluency for semantic lexical retrieval, Memory Binding Test for verbal episodic memory, and WAIS-IV subtests for processing speed (Coding), visual-spatial reasoning (Visual Puzzles), non-verbal abstract reasoning (Matrix Reasoning), verbal short-term memory and attention (Digit Span Forward) and working memory (Digit Span Backward and Sequencing). We defined three groups based on AoA (Early/Late) and proficiency (High/Low) of Catalan: 1) Early High-Proficiency bilinguals (n = 1559); 2) Late High-Proficiency bilinguals (n = 537) and 3) Late Low-Proficiency bilinguals, primarily Spanish-dominant (n = 319).

Results: Early and Late High-Proficiency bilingual groups outperformed Late Low-Proficiency bilinguals in verbal semantic fluency and processing speed. Additionally, Early High-Proficiency bilinguals scored significantly higher in verbal short-term memory than both Late AoA groups.

Conclusions: The effects of bilingualism are domain-specific and primarily driven by high proficiency and active language use rather than AoA alone. These findings suggest that maintaining high L2 proficiency throughout the lifespan contributes to cognitive reserve, enhancing attentional control and processing speed in healthy aging.