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Abstract
The main objective of the research at hand was to investigate the possible effects of two various inputs; that is to say, listening input vs. reading comprehension input on the incidental acquisition of new vocabulary among Iranian students of English as a foreign language at an intermediate level in Jahad language institute. For this purpose, in advance, OPT test was used among 60 to see who were qualified to be chosen for the purpose of this research in each group thus 30 subjects were selected in a random mode 15 of whom were assigned to the reading group and the rest were assigned as a listening group. All participants took a vocabulary pretest which tested their knowledge of the target words before implementing the treatment. The two groups, then, received two different treatments; reading treatment for the reading comprehension group and listening treatment for the listening group. The duration for an absolute and good result of each treatment was 15 sessions and each session lasted for 90 minutes. They then received a posttest with the aim of investigating the impacts of treatments on incidental vocabulary acquisition. The results of an independent sample t-test showed that both groups had positive impacts on the incidental acquisition of vocabulary; however, the listening group outperformed the reading tasks. The results of this research can have some implications for language teachers, curriculum developers, and English learners.