The main fact that is currently known about the nature of masked L2-L1 noncognate translation priming effects in the lexical decision task is simply that those effects are significant in some studies but not in others. In an effort to better understand these effects, we examined the data pattern for very proficient Japanese–English bilinguals using RT distributional analyses. We also examined the impacts of prime and target frequency on the priming effect. Significant priming was present even on the fastest trials, becoming larger on slower trials. Nonetheless, priming effects were generally constant across prime and target frequency with the only exception being when very high frequency L2 primes were used. In that situation, priming and target frequency were negatively related, a result that essentially produced the observed pattern of increasing priming on slower trials. Implications of these results and potential reasons for the presence/absence of L2-L1 priming effects are discussed.

Previous research with unbalanced, different-script bilinguals has typically produced null L2-L1 noncognate masked translation priming effects in lexical decision tasks (LDT). Two novel models of the bilingual mental lexicon have emerged to account for these null results: the episodic L2 hypothesis and the Sense model. In contrast, the BIA+ model predicts significant priming whenever bilinguals are sufficiently proficient in L2. Using Japanese–English bilinguals, the role of L2 proficiency in L2-L1 noncognate translation priming in an LDT was examined. In Experiments 1 and 2, significant priming effects were observed for highly proficient bilinguals. In contrast, in Experiment 3, less-proficient bilinguals produced a null priming effect. This pattern demonstrates that L2-L1 priming effects do arise in an LDT and those effects are modulated by L2 proficiency, consistent with the BIA+ model's expectations. The pattern can be also explained by the episodic L2 hypothesis, provided that certain modifications are made to its assumptions.

Previous priming studies suggest that, even for bilinguals of languages with different scripts, non-selective lexical activation arises. This lexical decision eye-tracking study examined contributions of frequency, phonology, and meaning of L1 Japanese words on L2 English word lexical decision processes, using mixed-effects regression modeling. The response times and eye fixation durations of late bilinguals were co-determined by L1 Japanese word frequency and cross-language phonological and semantic similarities, but not by a dichotomous factor encoding cognate status. These effects were not observed for native monolingual readers and were confirmed to be genuine bilingual effects. The results are discussed based on the Bilingual Interactive Activation model (BIA+, Dijkstra & Van Heuven, 2002) under the straightforward assumption that English letter units do not project onto Japanese word units.