Subliminal stimuli
A subliminal message is a signal or message designed to pass below (sub) the normal limits of perception. For example it might be inaudible to the conscious mind (but audible to the unconscious or deeper mind) or might be an image transmitted briefly and unperceived consciously and yet perceived unconsciously. This definition assumes a division between conscious and unconscious which may be misleading; it may be more true to suggest that the subliminal message (sound or image) is perceived by deeper parts of what is a single integrated mind.
The technology of subliminal messaging has been developed quite far e.g in the hemisphonic technologies of the Monroe Institute (see below) and such techniques have been used in very real world situations such as the rapid and comprehensive training of men in the armed forces to recognise foreign ships and aircraft.
In the everyday world, it has often been sugggested that subliminal techniques are used in advertising and for propaganda purposes (e.g. party political broadcasts).
A form of subliminal messaging commonly believed to exist involves the insertion of "hidden" messages into movies and TV programs. The concept of "moving pictures" relies on persistence of vision to create the illusion of movement in a series of images projected at 23 to 30 frames per second; the popular theory of subliminal messages usually suggests that subliminal commands can be inserted into this sequence at the rate of perhaps 1 frame in 25 (or roughly 1 frame per second). The hidden command in a single frame will flash across the screen so quickly that it is not consciously perceived, but the command will supposedly appeal to the subconscious mind of the viewer, and thus have some measurable effect in terms of behavior.
Origin of the Term
The term subliminal message was popularized in a 1957 book entitled The Hidden Persuaders by Vance Packard. This book detailed a study of movie theaters that supposedly used subliminal commands to increase the sales of popcorn and Coca-Cola at their concession stands. However, this study was proven to be completely false, and the author of the study, James Vicary, was unable to reproduce these results in any further tests.
In 1973 the book Subliminal Seduction claimed that subliminal techiques were in wide use in advertising. This led to a widespread popularization of the concept of subliminal commands. The public hysteria over its supposed use was enough to lead the Federal Communications Commission to declare subliminal advertising "contrary to the public interest," whether the technique actually worked or not.
Validity
There is no doubt that subliminal messages can be perceived and that the technology of subliminal learning or influencing exists e.g. in the more sophisticated subliminal tapes and CD's that are commercially available.
With regard to the question of whether subliminal messages are widely used to influence groups of people e.g. audiences, there is little evidence that the technology has ever been used on a mass audience (other than its occasional use by artists who use it to make an artistic statement). The current consensus among marketing professionals is that subliminal advertising is ineffective and can be counter-productive.
see also: advertising, marketing, promotion