Intelligibility of first-language (L1) and second-language (L2) speech by switched-dominance Spanish-English bilinguals.

Recordings of Spanish and English sentences by switched-dominance bilingual (SDB) Spanish (i.e., L2-dominant Spanish-English bilinguals) and by L1-dominant Spanish and English controls were presented to L1-dominant Spanish and English listeners, respectively. At -4 dB signal-to-noise ratio (SNR), Spanish and English productions by SDBs were equally intelligible with both reaching L1-dominant control levels. At -8 dB SNR, SDB English intelligibility matched that of L1-dominant English controls, yet SDB Spanish intelligibility was significantly lower than that of L1-dominant Spanish controls. These results emphasize that extended (but not early) exposure is both necessary and sufficient for robust speech learning.