Drawing on Robinson’s cognition hypothesis, the study attempted to examine how task conditions influence EFL learners’ oral performance and whether learners’ individual differences in terms of tolerance of ambiguity and self-efficacy mediate the effects of such conditions. To this end, 62 Iranian intermediate EFL learners from private language institutes in Tehran performed four dyadic decision-making tasks manipulated along task conditions of information distribution and goal orientation. Their performance was measured through complexity, accuracy and fluency (CAF) indices. Their tolerance of ambiguity and self-efficacy were assessed using separate questionnaires. The results indicated that information distribution and goal orientation could significantly impact the participants’ performance on the tasks. As to the CAF indices, it seemed that Skehan’s (2016) trade-off hypothesis was a better fit than Robinson’s (2015) cognition hypothesis since trade-offs were found between complexity and accuracy/fluency. The results of the correlations revealed that there were a number of significant positive relationships between tolerance of ambiguity and the CAF indices on the one hand and self-efficacy and the CAF indices on the other. While the former relationships did not confirm the specific prediction of the cognition hypothesis, the latter relationships did. Overall, the findings contribute to Robinson’s hypothesis concerned with the effects of task conditions on oral performance and the mediating role of individual differences, and have implications for task sequencing and task-based teaching.
