Subliminal Messages

E.W. Scripture published in 1898 The New Psychology, which described the basic principles of subliminal messages. In 1900, Knight Dunlap, an American professor of psychology, flashed an "imperceptible shadow" to subjects while showing them a Müller-Lyer illusion containing two lines with pointed arrows at both ends which create an illusion of different lengths.

Dunlap claimed that the shadow influenced his subjects subliminally in their judgment of the lengths of the lines. Although these results were not verified, American psychologist Harry Levi Hollingworth reported in an advertising textbook that such subliminal messages could be used by advertisers.

During World War II, the tachistoscope, an instrument which projects pictures for an extremely brief period, was used to train soldiers to recognize enemy airplanes. Today the tachistoscope is used to increase reading speed or to test sight.

The practice of subliminal advertising was subsequently banned in the United Kingdom and Australia, and by American networks and the National Association of Broadcasters in 1958.

In 1973, commercials in the United States and Canada for the game Husker Du? flashed the message "Get it". During the same year, Wilson Bryan Key's book Subliminal Seduction claimed that subliminal techniques were widely used in advertising. Public concern was sufficient to cause the FCC to hold hearings in 1974.

The hearings resulted in an FCC policy statement stating that subliminal advertising was "contrary to the public interest" and "intended to be deceptive". Subliminal advertising was also banned in Canada following the broadcasting of Husker Du? ads there. A study conducted by the United Nations concluded that "the cultural implications of subliminal indoctrination is a major threat to human rights throughout the world."

Some messages are presented to the listener backwards. While listening to a normal forward message (often somewhat nonsensical), one is simultaneously being treated to a back-wards message (in other words, the lyric sounds like one set of words going forward, and a different set of words going backwards). Some experts believe that while the conscious mind is absorbing the forward lyric, the subconscious is working overtime to decipher the backwards message.

Subconscious stimulus by single words is well established to be modestly effective in changing human behavior or emotions. However there is no strong evidence that messages in advertising can or have been used effectively.

Perception of subliminal messages is a type of subconscious cognition. Unlike unconscious tasks such as attending to one signal in a noisy environment while keeping track of other signals (e.g., listening to one voice out of many in a crowded room) and automatic tasks such as breathing, subliminal message cognition cannot be done consciously.

An important question about subliminal perception is: How much of the message is perceived? That is, is the whole message sensed and fully digested, or are only its main and simpler features? There are at least two schools of thought about this. One of them argues that only the simpler features of unconscious signals could be perceived. The second school of thought argues that unconscious cognition is comprehensive and that much more is perceived than can be verbalized.

Proponents of the power of subliminal messages claim they gain influence or power from the fact that they circumvent the critical functions of the conscious mind, and therefore subliminal suggestions are potentially more powerful than ordinary suggestions. This route to influence or persuasion would be akin to auto-suggestion or hypnosis, wherein the subject is encouraged to be (or somehow induced to be) relaxed so that suggestions are directed to deeper (more gullible) parts of the mind; some observers have suggested that the unconscious mind is incapable of critical refusal of hypnotic or subliminal suggestions.

However, critics of the theory have suggested that the effect of subliminal messages would at best be no more than that of a glimpse of a billboard in the corner of an eye. Controlled experiments that attempt to demonstrate the influence of subliminal messages generally find little to no effect.

The book Mind Hacks by O'Reilly Press states that subliminal messages are effective in "priming" (putting a half-processed idea in the mind, leading to increased familiarity or a "tip of the tongue" situation where the idea is present but is not articulated until triggered). It also states that for this reason it has limited application in persuasion, and only slightly more use in advertising. The text states that additionally only one word or image is perceived subliminally most of the time, and that the primary way in which it can be used in advertising is by creating a familiarity with a product that has not been seen before, familiarity that could be misinterpreted as preference. The text references an experiment in which faces were flashed subliminally before the test subject rated a group of faces as to which were preferable—this experiment can be duplicated online, through the URL given in the book.

In 2006, a study by Dr. Johan Karremans at the University of Nijmegen suggested that subliminal messaging may have an effect when the message is goal-relevant. In their experiments, half of the participants was subliminally primed with Lipton Ice (i.e., "Lipton Ice" was repeatedly flashed on a computer screen for 24 milliseconds), while the other half was primed with a control non-word. Subsequently, the prime positively influenced participants' choice for Lipton Ice over another soft drink, but only for participants who already were thirsty. Participants who were not thirsty were not influenced by the subliminal messages.