7 Nielsen L (1988) Spatial Relations in Congenitally Blind Infants. Refsnaeeskolen, Denmark
For further information on these techniques, the reader is invited to refer to the original sources such as:
van Dijk J (1965) The first steps of deaf-blind children towards language. Proceedings of Conference on the Deaf-Blind: Refsnaesskolen Denmark. Boston: Perkins School for the Blind.
van Dijk J (1967) The non verbal deaf-blind child and his world: his outgrowth towards the world of symbols. Holland: Institute for the Deaf
van Dijk J (1986) An educational curriculum for deaf-blind multi-handicapped per sons, In D Ellis (ed) Sensory Impairments in mentally handicapped people. London, Croom-Helm.
Other authors have taken up these themes applying them in broadly similar contexts.