In media studies, media psychology, communication theory and sociology, media influence and media effects are topics relating to mass media and media culture effects on individual or audience thought, attitudes and behavior.
Media influence is the actual force exerted by a media message, resulting in either a change or reinforcement in audience or individual beliefs. Media effects are measurable effects that result from media influence, or a media message. Whether that media message has an effect on any of its audience members is contingent on many factors, including audience demographics and psychological characteristics. These effects can be positive or negative, abrupt or gradual, short-term or long-lasting. Not all effects result in change: some media messages reinforce an existing belief. Researchers examine an audience after media exposure for changes in cognition, belief systems, and attitudes, as well as emotional, physiological and behavioral effects.
There are several scholarly definitions of media effects. Bryant and Zillmann defined media effects as "the social, cultural, and psychological impact of communicating via the mass media". Perse stated that media effects researchers study "how to control, enhance, or mitigate the impact of the mass media on individuals and society". Lang stated media effects researchers study "what types of content, in what type of medium, affect which people, in what situations".
Media effects studies have undergone several phases, often corresponding to the development of mass media technologies.
From the early 20th century to 1930s, developing mass media technologies, such as radio and film, were credited with an almost irresistible power to mold an audience's beliefs, cognition and behaviors according to the communicators' will. The basic assumption of strong media effects theory was that audiences were passive and homogeneous. This assumption was not based on empirical evidence but on assumptions of human nature. There were two main explanations for this perception of mass media effects. First, mass broadcasting technologies were acquiring a widespread audience, even among average households. People were astonished by the speed of information dissemination, which may have clouded audience perception of any media effects. Secondly, propaganda techniques were implemented during the war time by several governments as a powerful tool for uniting their people. This propaganda exemplified strong-effect communication. Early media effects research often focused on the power of this propaganda (e.g., Lasswell, 1927). Combing through the technological and social environment, early media effects theories stated that the mass media were all-powerful.