How does parallel language activation affect switch costs during trilingual language comprehension?

Declerck, M., Koch, I., Dunabeitia, J., Grainger, J., & Denise, N. [(2019). What absent switch costs and mixing costs during bilingual language comprehension can tell us about language control?Journal of Experimental Psychology Human Perception & Performance.] assumed that the absence of switch costs in bilingual language comprehension may be due to little degree of parallel language activation while substantial degree of it may lead to switch costs. This study tested this assumption by examining the switch costs during Russian-English-Chinese trilinguals' performing lexical decision tasks in language pairs of L1-L2 in Experiment 1a, L1-L3 in Experiment 1b and L2-L3 in Experiment 1c. We found switch costs in L2 in Experiment 1a and switch costs in both L1 and L3 in Experiment 1b, but no switch costs in both L2 and L3 in Experiment 1c. These results generally provided evidence for the account.