In what decade did Jean Piaget develop and propose his theories of cognitive development?

Jean Piaget developed and proposed his theories of cognitive development primarily throughout the 1930s to the 1950s. His most significant works on the topic were published during these decades, with the most notable being "The Origins of Intelligence in Children" in 1952. Therefore, the correct time period aligns more decidedly with the earlier part of the 20th century, rather than in the 1990s or later decades.

The confusion might lie in the timeline of when his theories gained widespread recognition and influence within developmental psychology. However, if considering the actual period of development and initial publication, the correct decade does not fall within the choices provided or the selected answer. Instead, Piaget's foundational work laid the groundwork for much of the research and discourse that followed in later years, including those decades mentioned.