More than use it or lose it: the number-of-speakers effect on heritage language proficiency.

Acquiring a heritage language (HL), a minority language spoken primarily at home, is often a major step toward achieving bilingualism. Two studies examined factors that promote HL proficiency. Chinese-English and Spanish-English undergraduates and Hebrew-English children named pictures in both their languages, and they or their parents completed language history questionnaires. HL picture-naming ability correlated positively with the number of different HL speakers participants spoke to as children, independently of each language's frequency of use, and without negatively affecting English picture-naming ability. HL performance increased also when primary caregivers had lower English proficiency, with later English age of acquisition, and (in children) with increased age. These results suggest a prescription for increasing bilingual proficiency is regular interaction with multiple HL speakers. Responsible cognitive mechanisms could include greater variety of words used by different speakers, representational robustness from exposure to variations in form, or multiple retrieval cues, perhaps analogous to contextual diversity effects.