Similar to Krashen's input hypothesis, the interaction hypothesis claims that comprehensible input is important for language learning. In addition, it claims that the effectiveness of comprehensible input is greatly increased when learners have to negotiate for meaning. This occurs when there is a breakdown in communication which interlocutors attempt to overcome. One of the participants in a conversation will say something that the other does not understand; the participants will then use various communicative strategies to help the interaction progress. The strategies used when negotiating meaning may include slowing down speech, speaking more deliberately, requests for clarification or repair of speech, or paraphrases. Interactions often result in learners receiving negative evidence. That is, if learners say something that their interlocutors do not understand, after negotiation the interlocutors may model the correct language form. In doing this, learners can receive feedback on their production and on grammar that they have not yet mastered. The process of interaction may also result in learners receiving more input from their interlocutors than they would otherwise. Furthermore, if learners stop to clarify things that they do not understand, they may have more time to process the input they receive. This can lead to better understanding and possibly the acquisition of new language forms. Finally, interactions may serve as a way of focusing learners' attention on a difference between their knowledge of the target language and the reality of what they are hearing; it may also focus their attention on a part of the target language of which they are not yet aware.
Primacy of interaction
Although there are several studies that link interaction with language acquisition, not all researchers subscribe to the idea that interaction is the primary means by which language proficiency develops. In a survey of the literature on the subject, Larsen-Freeman and Long say that interaction is not necessary for language acquisition; they do say, however, that it helps in certain circumstances. Gass and Selinker claim that as well as interaction facilitating learning, it may also function as a priming device, "setting the stage" for learning rather than being the means by which learning takes place. In addition, Ellis notes that interaction is not always positive. He says that sometimes it can make the input more complicated, or produce amounts of input which overwhelm learners. According to Ellis, this can happen if interlocutors use lengthy paraphrases or give complex definitions of a word that was not understood, and he comes to the conclusion that the role of interaction in language acquisition is a complex one.
