This document discusses the four eras of mass communication theories:
1) Era of mass society theory from 1850-1940 where new media was seen as disruptive.
2) Era of scientific perspective from 1940-1950 where Lazarsfeld conducted experiments showing media had limited effects.
3) Era of limited effects from 1950-1960s where research supported this perspective.
4) Era of cultural criticism from 1960-1980s where European theorists argued media enabled elites to maintain power. Theories discussed in each era include propaganda theory, limited effects theory, agenda setting theory, and cultivation theory.