The language threshold effect on comprehending an L2 (second language) text was experimentally examined, using two types of measurement tool, multiple-choice & true/false questions and a recall task for L2 reading comprehension. Cognitive processes implicated in each measure were delineated to allow a finer analysis on the role of L1 reading competence and L2 proficiency in comprehending an L2 text. In order to observe how one aspect of L2 proficiency, vocabulary knowledge, is related to language threshold effect, thirty-two 9th grade Korean students in Korea were given a vocabulary knowledge acquisition activity in a treatment condition between a pretest and a posttest. The relative contributions that L1 reading competence and L2 proficiency made to L2 reading comprehension were analyzed before the treatment and after the treatment using multiple-regression analysis technique. The findings of this repeated measure design were consistent with previous correlational studies showing that the role of L1 reading competence became stronger as L2 proficiency operationalized via vocabulary knowledge improved. What is elaborated in the present study is the fact that cognitive processes, initiated by a recall task, are more sensitive to the weakening of language threshold effects.