Activity theory
Activity theory (AT; ) is an umbrella term for a line of eclectic social sciences theories and research with its roots in the Soviet psychological activity theory pioneered by Lev Vygotsky , Alexei Leont'ev and Sergei Rubinstein. These scholars sought to understand human activities as systemic and socially situated phenomena and to go beyond paradigms of reflexology (the teaching of Vladimir Bekhterev and his followers) and classical conditioning (the teaching of Ivan Pavlov and his school), psychoanalysis and behaviorism. It became one of the major psychological approaches in the former USSR, being widely used in both theoretical and applied psychology, and in education, professional training, ergonomics, social psychology and work psychology.
Cultural-historical activity theory
In his 1987 ""Learning by expanding"", Engeström offers a very detailed account of the diverse sources, philosophical and psychological, that inform activity theory. In subsequent years, however, a simplified picture has emerged from his and other researchers' work, namely the idea that (to date) there are three principal 'stages' or 'generations' of activity theory, or "cultural-historical activity theory (CHAT). Whilst the first generation built on Vygotsky's notion of mediated action, from the individual's perspective, and the second generation built on Leont'ev's notion of activity system, with emphasis on the collective, the third generation, which appeared in the mid-nineties, builds on the idea of multiple interacting activity systems focused on a partially shared object, and boundary-crossings between them.