This study examined the effects of input-oriented and output-oriented tasks with different involvement load indices on Iranian EFL learners' comprehension and production of lexical collocations. To achieve this purpose, a sample of 180 intermediate-level EFL learners (both male and female) participated in the study. The participants were in six experimental groups. Each of the groups was randomly assigned to one of the experimental conditions, namely input-oriented tasks with involvement load 1 (True-false), 2 (Matching), 3 (Multiple-choice), and output-oriented tasks with involvement load 1 (Short response), 2 (Fill in the blanks), and 3 (Sentence formation). At the end of the treatment period, the researchers administered a 40-item test in multiple-choice format and a 40-item test in fill-in-the-blanks format to assess the participants' comprehension and production of collocations. The collected data were analyzed using two different two-way ANOVAs and a series of independent-samples t-tests. The results showed that the tasks with higher involvement load indices were more effective on both receptive and productive knowledge of lexical collocations. The results also revealed that output-oriented tasks were more beneficial than input-oriented tasks at all three indices of involvement load. These findings can have theoretical and pedagogical implications for language teachers, researchers, and learners.
