This study examined whether changes in proficiency balance between the source languages and the target language of trilinguals modulate the cognate facilitation effect. Participants were Arabic–Hebrew–English different-script trilinguals who were partially immersed in an L2 speaking environment. For three consecutive years, 88 university students completed a battery of subjective and objective proficiency tasks in each of their languages and a semantic relatedness task in English, including cognate and control primes. Results showed that the comparable cognate facilitation across double (L1–L3 and L2–L3) and triple (L1-L2-L3) cognate items remained stable across all three timepoints, despite increases in L2 proficiency. These findings indicate that in a semantic task, facilitation can occur through the L1, the L2 or both, and that increases in source-language proficiency do not necessarily lead to increases in cross-language influences from that language.
