In the present study, two different models of task complexity; namely, limited attentional capacity model and cognition hypothesis were examined. To this end, the manipulation of cognitive task complexity along +/- single task dimension on Iranian EFL learners’ production in terms of fluency was explored. Based on the results of the writing test of TOFEL (2004), 48 learners were selected as the participants of the study and were divided into two groups, simple task group (STG, n=24) and complex task group (CTG, n=24). The participants in the STG were given an eight-frame picture which had been arranged in the correct sequence before its administration (+ single task). The participants in the CTG were given all the eight frames which were not arranged in their correct order. These participants were required to order the frames in the right sequence first, before starting writing (- single task). Their output was encoded based on the measure of fluency. One independent sample t-tests was run. The results indicated that the participants significantly generated more words in the complex task. Based on the findings, it can be concluded that in the Iranian context, the predictions of limited attentional capacity model were more accurate.
