Nikolay Veresov

Research and clinical practice in the field of defectology is a significant part of Vygotsky's scientific legacy. In the current literature, however, defectological studies and cultural-historical theory (CHT) are discussed separately from each other. Vygotsky's defectological research was one of the sources of the creation of the general CHT and therefore provides a key to a more comprehensive understanding of this theory. Three key findings from the research and clinical practice in the field of defectology are of interest: 1) Secondary disability which was further developed as a concept of social environment as a source of psychological development: 2) Roundabout ways of overcoming disability further improved in the concept of two lines of development and 3) Incongruence that was developed into theoretical concept of cultural sign as a psychological and “tool and principle of signification that is creation and use of signs”. On the other hand, the main concepts of CHT influenced significantly the understanding of the nature of developmental defects and the development of new methods of special education.