The study reported in this paper aims to compare the comprehension of two groups of adult EFL Iranian students on a reading passage under two input conditions: linguistically modified input, characterized by both lexical and syntactic simplification, and interactionally modified input with no linguistic modifications but with opportunities for interaction with the teachers. The results of the study revealed that the students who were allowed to seek clarification by asking questions had comprehended the text better than the students who had read the simplified version of the text. The conclusions drawn from the findings of this study are threefold: they lend empirical support to Long's Interaction Hypothesis, recommend interactional approach to teaching reading, and promote the use of authentic reading materials. It is a widely accepted fact that in order to learn a language, one must receive the necessary data. In acquiring their first language, children receive a large quantity of L1 data from their parents and the surrounding environment. In learning a second language, the majority of the learners receive the L2 data from language classes. This data is provided to them through two main sources of input, i.e. the teacher and the textbook. This paper is intended to review the related literature on input in Second Language Acquisition (SLA) and find out what kind of input is best comprehended by language learners.
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