作者：刘钰茗
　　【Abstract】Interaction is a concept focusing on the outside factors used to explore its influence on second language acquisition （SLA）. Ellis（1985） gives its definition as “interaction consists of the discourse jointly constructed by the learner and his interlocutors”（p.127）. And from interactionist view， language acquisition is a process including the common action of mental internalization and environment impact. This article aims to focus on interaction and one of its relevant theories： sociocultural theory （SCT） to explore its application in English class teaching.
　　【Key words】interaction； scaffolding； ZPD； sociocultural theory
　　【作者簡介】刘钰茗，南京师范大学中北学院，硕士研究生，助教，研究方向：二语习得的社会文化观，二语习得者的动机。
　　1. Theory associated with the topic
　　One of the alternative views concerning about the role of interaction in SLA is based on Sociocultural Theory （Vygotsky 1978） SCT. The theory is about the development of people’s cognition and high mental ability， which is mainly achieved through social interaction （Liang， 2013）.
　　And according to Lantolf （2007）， the principles of SCT can be also applied to explain SLA. The core concept of sociocultural approaches is that interaction is an indispensable force of SLA but not just a factor facilitating SLA，， and all language learning happens in a social setting with a combined action from inside and outside （Swain， Kinnear & Steinman， 2011）. Furthermore， in terms of the key meaning of SCT， it is different from social approaches in which interaction is seen as a helpful element for SLA but not a key force （Saville-Troike， 2006）.
　　From the sociocultural perspective， second language learning occurs when there is a transformation from a person’s current inner knowledge structures to higher and complex mental functions. And this process must involve medication， which is the basic claim of SCT （Lantolf， 2009）. This kind of medication needs to occur in a level which is called the Zone of Proximal Development （ZPD）. This metaphor term refers to a gap between the stage learners can perform independently and a higher level where learners need to achieve with outside assistance or mediation.
　　SCT emphasizes that SLA is a process of mediation. And mediation is categorized into three aspects： other-mediation， self-mediation and the mediation of cultural artifacts （Bruner， 1986）. Other-mediation occurs between experts and novices or between a proficient second language speaker and another speaker in a low level. And one of the types is scaffolding which is a kind of support from experts and peers who are in an advanced level of SLA.