Drawing on influences such as Humboldt and Friedrich Nietzsche, some European thinkers developed ideas similar to those of Sapir and Whorf, generally working in isolation from each other. Prominent in Germany from the late 1920s through into the 1960s were the strongly relativist theories of Leo Weisgerber and his key concept of a 'linguistic inter-world', mediating between external reality and the forms of a given language, in ways peculiar to that language. Russian psychologist Lev Vygotsky read Sapir's work and experimentally studied the ways in which the development of concepts in children was influenced by structures given in language. His 1934 work ""Thought and Language"" has been compared to Whorf's and taken as mutually supportive evidence of language's influence on cognition. Drawing on Nietzsche's ideas of perspectivism Alfred Korzybski developed the theory of general semantics that has been compared to Whorf's notions of linguistic relativity. Though influential in their own right, this work has not been influential in the debate on linguistic relativity, which has tended to center on the American paradigm exemplified by Sapir and Whorf.