Search for hypnosis recordings and you will soon find the subliminal kind. Hours of rain or music with, it is claimed, thousands of affirmations hidden beneath, too quiet or too fast to hear. Play them while you sleep or work and they will reprogramme your subconscious, effortlessly.
It is an appealing idea. The evidence against it is unusually clear.
The popcorn that never was
The modern belief in subliminal persuasion began with a single story.
In 1957 an American market researcher, James Vicary, announced that he had flashed the words “Eat popcorn” and “Drink Coca-Cola” on a cinema screen during a film, for a fraction of a second, too briefly to be noticed. He claimed that popcorn sales rose by 57.8 per cent and Coca-Cola by 18.1 per cent.
The reaction was enormous. There was public alarm about mind control, and broadcasters in several countries moved to ban the technique.
There was one problem. Other researchers could not reproduce the result, and the cinema manager reportedly said no such test had been done. In 1962, in an interview with the trade magazine Advertising Age, Vicary admitted that the study was a gimmick. The data had been invented to drum up business for his failing consultancy.
The experiment that launched a worldwide belief never happened.
The self-help tapes
By the 1980s subliminal self-help recordings were a large industry, promising weight loss, better memory, confidence and more.
In 1991 the psychologist Anthony Greenwald and colleagues tested them properly. They recruited 237 people who wanted the benefits on offer, and gave them commercial subliminal tapes claimed to improve either memory or self-esteem. Participants used them for a month, following the manufacturers’ instructions.
The clever part was the labelling. Half the tapes had been deliberately mislabelled. Some people who thought they were listening to a memory tape were actually hearing the self-esteem one, and the reverse.
The results:
- Neither tape produced its claimed effect. The memory tape did not improve memory. The self-esteem tape did not improve self-esteem.
- Everyone improved a little on both measures, whichever tape they had. A general placebo effect.
- More than a third believed they had improved in the area named on the label, whatever was actually on the tape.
People who thought they had a memory tape felt their memory was better. What they believed mattered. What was on the recording did not.
Other studies reached the same conclusion, and analyses of some commercial tapes found no detectable speech in them at all.
Is subliminal perception real at all?
Yes, in a limited way, and this is where the confusion comes from.
Laboratory research shows that a word or image presented too briefly to be consciously seen can still have small, short-lived effects. It can make a related word slightly quicker to recognise a moment later. This is called subliminal priming.
But the effects are:
- Tiny
- Brief, fading within seconds or less
- Limited to very simple things, such as single words
- Dependent on precise laboratory conditions
Some studies suggest that a subliminal prime can nudge a choice a person is already inclined towards: showing the name of a drink might slightly influence someone who is thirsty. Nothing in this research shows that complex sentences can be absorbed, or that anyone’s habits or personality can be changed.
Why recordings cannot work as claimed
- Speech has to be heard to be understood. If a message is masked so that you cannot make out the words, your brain cannot make them out either. There is no separate, more acute listener inside.
- Sped-up or backwards speech is not decoded unconsciously. Tests of “backward masking” in music found people could not understand reversed messages.
- Sleep learning does not work in the way claimed. A sleeping brain does not take in new verbal information to any useful degree.
- Suggestion needs attention. Everything known about hypnosis says that suggestions work when a person attends to them and goes along with them.
Why people swear by them
- Placebo and expectation. You have paid, you are hopeful, and you are paying more attention to the problem.
- The pleasant sound. Rain or soft music is relaxing, and relaxation helps many things.
- The commitment itself. Deciding to change, and listening daily, is a behaviour change.
- Confirmation bias. Improvements are credited to the recording.
- The label. As Greenwald showed, believing it is a confidence tape is enough to feel more confident.
If it helps, that is fine, but ordinary relaxing music would do as well and cost nothing.
Subliminal versus hypnosis
They are often sold side by side, and they are opposites.
| Subliminal recordings | Hypnosis | |
|---|---|---|
| Suggestions | Hidden | Heard clearly |
| Attention | Not required | Essential |
| Your role | Passive | Active |
| Consent to content | You cannot know what is said | You know and agree |
| Evidence | Controlled trials found no effect | Good evidence for several problems |
Honest hypnosis has nothing hidden in it. You should always be able to hear, and ideally read, every suggestion.
A point about trust
With a subliminal recording you are taking the seller’s word for what is on it. You cannot check. That alone is a reason for caution.
What to use instead
- A recording with audible suggestions you have read and agree with
- A script you write and record yourself
- Plain relaxing sound, if that is what you enjoy
- For real problems, an approach with evidence behind it
The bottom line
The famous popcorn experiment was invented, and when subliminal self-help tapes were properly tested they did nothing beyond placebo. Suggestions work when you hear them, understand them and take part. If you cannot hear it, it is not doing anything.
Next in the series: Do Binaural Beats Work? What the Research Says
This article is for general information and is not medical advice.