This study examines the cognitive processes underlying the comprehension of L2 idiomatic expressions by using two different visual instructional techniques -- pictorial representation of literal meanings versus pictorial representation of figurative meanings of each idiomatic expression -- considering two settings (EFL vs. ESL), two different types of idioms (opaque vs. transparent) and two different proficiency levels (intermediate vs. advanced). The treatment included common pedagogical practices that use Dual Coding Theory as two different visual techniques with verbal support to teach different types of idioms. 67 ESL and 63 EFL learners attended the study. Idiom Comprehension Test was used before and after the treatment. Results of repeated-measure ANOVA based on pre- and post-test comparisons revealed that the comprehension of L2 idioms differed with respect to the learning setting, instructional technique, and idiom type. Nevertheless, proficiency level did not seem to have any effect on comprehension outcomes of any group. The results showed that in the ESL setting, the figurative technique was more successful than literal technique; while in EFL setting the literal technique resulted in better scores compared to figurative technique. ESL learners were better at learning idioms with opaque meanings than learners in EFL settings whereas EFL students were better at learning idioms with transparent meanings. The results of this study support the view of the Dual Idiom Representation Model stating that ESL learners activate their existing idiom entry and they comprehend figuratively whereas EFL learners must decompose idioms.