Exposure duration is the main determinant of bilinguals' vocabulary knowledge

The present study examines whether age of second language acquisition, duration of exposure to that language, and chronological age determine vocabulary knowledge in 214 Russian-Hebrew bilinguals (ages 19-80, immigration ages 1-46, and exposure duration 7-63 years). Participants reported their language background and completed a multiple-choice vocabulary test in Hebrew, alongside other objective tests of Russian and Hebrew proficiency. While vocabulary scores were below age-matched norms for native Hebrew speakers, they were similar to those of younger native speakers matching in exposure duration. Raw vocabulary scores were similar whether participants immigrated up to age 15 or after that age, although results indicated a negative association between age of immigration and vocabulary scores. A positive association emerged between exposure duration and vocabulary scores, and when analyzing all measures together, age of immigration did not predict vocabulary scores, whereas exposure duration was its main determinant. We suggest that bilingualism itself does not cause a vocabulary gap, and that bilinguals' vocabulary knowledge in their second language improves with exposure, as it does in native speakers throughout adulthood. The study emphasizes that learning a foreign language requires extensive exposure and that vocabulary learning is a lifelong process.