Discovered in 1949 by Carl Hovland, Arthur A. Lumsdaine, and Fred D. Sheffield, the sleeper effect manifests as a shift in the influence exerted on consumer attitudes over time, following exposure to a positive or negative source. This phenomenon occurs particularly when the message originates from a source that is either unreliable or unidentified by the consumer, and is influenced by the consumer’s selectivity and limited memory capacity. Gradually, a dissonance develops between the elements of the message and the message itself, thus reinforcing the retention of the knowledge conveyed by the message, while counteracting the initially prevented attitude change. According to research by David Mazursky and Yaacov Schul published in 1988, the sleeper effect occurs primarily when the complex structure of the message offers more memorization opportunities than the original source.