The present study asked if bilinguals who are immersed in their nondominant language are more likely to know some words only in their nondominant language.

The either-language scoring benefit (ELSB) reflects how many more points bilinguals get when credited for pictures named regardless of which language is used. We asked if the ELSB varies with self-rated proficiency level of the nondominant language in young English-dominant (n = 68) compared to Spanish-dominant (n = 33) bilinguals, and in older English-dominant (n = 36) compared to Spanish-dominant (n = 32) bilinguals. All bilinguals were immersed in English (in the USA) at the time of testing.

Spanish-dominant bilinguals showed a larger ELSB than English-dominant bilinguals (in both young and older groups), but simple correlations showed that the degree of Spanish dominance was associated with a higher ELSB only in young bilinguals. Additionally, the ELSB was larger for bilinguals with more years of immersion and for more balanced bilinguals, whether measured by naming scores or self-rated balance (in both age groups). Nearly half (n = 14/33) of the young bilinguals who said they were Spanish-dominant scored higher in English than in Spanish, and on average these participants had similar naming scores in English and Spanish.

Either-language scoring benefits bilinguals with higher proficiency level in the nondominant language, which is more likely in bilinguals with extended immersion in the nondominant language, who also tend to be more balanced bilinguals, and for young adult bilinguals who may be in the process of a switch in which language is dominant.