Subliminal Influence

In psychology, subliminal means below the threshold of conscious perception. Many people believe that advertising and media use techniques that cannot consciously be seen or heard but nevertheless act on the subconscious mind.

Being critical of such claims does not, of course, mean being blind or naive. There are enough unscrupulous businesspeople and power-hungry politicians who would gladly send messages into the subconscious minds of unsuspecting victims if this worked reliably and effectively. Perhaps some try anyway.

Origins of the myth

The roots of the debate reach back to the beginning of the twentieth century. The Müller-Lyer illusion was also invoked in this context. Experiments involving barely perceptible stimuli were used to argue that people respond to information below the threshold of consciousness.

The decisive question, however, is not whether unconscious processing exists in principle. The question is how strong, reliable and generalizable a claimed effect really is.

Vicary, popcorn and Coca-Cola

The idea became widely popular in the late 1950s. Advertising researcher James Vicary claimed that he had flashed extremely brief messages such as “Eat Popcorn” and “Drink Coca-Cola” during film screenings. The audience supposedly could not consciously perceive the messages, yet sales of popcorn and cola were said to have increased substantially.

Stories of this kind contain all the ingredients of a modern myth: an invisible technology, unsuspecting subjects and a spectacular effect. The case later became an example of why dramatic claims should not be believed merely because percentages are quoted.

Attempts to reproduce the effect under more controlled conditions did not reveal the alleged simple remote control of purchasing behaviour.

The Canadian “Phone Now” episode

In an often-cited television episode, the subliminal instruction “Phone Now” was repeatedly inserted. The punchline of the story is almost comic: the expected wave of telephone calls did not occur. When viewers were later asked to guess what message had been used, there was likewise no miraculous display of secret perception.

What follows — and what does not?

An important logical distinction is needed here. From the possibility that stimuli can be processed unconsciously under certain experimental conditions, it does not follow that complex actions, motives, political convictions or purchasing decisions can be programmed at will.

Unconscious processing can exist.
Small, short-lived and context-dependent effects are not the same as robust remote control.
The more spectacular the claimed effect, the stronger the evidence must be.

Backmasking

A related idea is so-called backmasking: messages allegedly hidden in music by playing material backwards or concealing it in other ways are said to influence behaviour. Accusations against rock bands became especially well known.

Again, discovering what sounds like a message is not evidence that the message was unconsciously understood and then caused complex behaviour.

Subliminal fear and a sarcastic counter-question

It has repeatedly been claimed that television broadcasters or other media use subliminal advertising. My old counter-question was deliberately sarcastic: if invisible advertising is so overwhelmingly effective, why do broadcasters additionally torment us with visible, lengthy and expensive advertising?

That is not, of course, a formal proof against every conceivable subliminal effect. It is an ironic plausibility test directed at the far-reaching claim of almost arbitrary secret manipulation.

The story becomes especially charming when a visible beer commercial is allegedly also advertising Pepsi in secret. Does that seem sensible to you? It does not to me either.

New business opportunities

Fear of subliminal manipulation also created a business model. Instead of secretly inducing consumers to buy other products, one now sells products that are themselves supposedly enriched with subliminal messages.

Promised outcomes include, for example:

becoming a non-smoker through music files or CDs containing inaudible messages;
greater self-confidence, happiness or sexual performance;
self-hypnosis combined with so-called binaural beats;
far-reaching physical changes through messages allegedly routed directly past conscious awareness.

From the seller’s perspective, one especially convenient feature of such products is that the crucial messages often cannot be perceived or unambiguously extracted by technical means. What cannot be demonstrated is also difficult to refute — a familiar pattern in pseudoscientific sales arguments.

Conclusion

The reasonable conclusion is not: “Unconscious processing does not exist.” Nor is it: “Anything presented subliminally can remotely control people.”

The concrete claim is what matters. What effect is being claimed? How large is it? Under what conditions does it occur? Has it been independently reproduced? And is the conclusion actually supported by the data?

Literature and historical reference points

Anthony R. Pratkanis: The Cargo Cult Science of Subliminal Persuasion, Skeptical Inquirer, 1992.
Timothy E. Moore: Subliminal Perception: Facts and Fallacies, Skeptical Inquirer, 1992.
Timothy E. Moore and Anthony R. Pratkanis: work on subliminal influence and its evaluation.
W. Weir: Another Look at Subliminal “Facts”, Advertising Age, 1984.