According to Vygotsky,
The central fact about our psychology is the fact of mediation.
Vygotsky claimed that humans do not act upon their environment directly, but rather through the use of tools. Mediation is defined as the use of tools as a "buffer" between the individual and the outside world (Lantolf & Thorne, 2007).
Our knowledge of the world is therefore mediated by symbols and other psychological tools.
Classroom illustration: Video games for SLA