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Subliminal stimuli refer to unconscious perception of words or images that influence behavior without awareness. The theory behind subliminal stimuli producing an emotional response hinges on the speed at which these hidden messages are embedded into other stimuli. Hundreds of research studies exploring the concept of unconscious perception and its effect on behavior failed to produce evidence that the phenomenon exists.
People with certain neurological disorders, and the effects of anesthesia, might guide decisions based on subliminal stimuli, researchers found. Patients suffering from blindsight, a disorder marked by damage in an area of the brain that controls visual perception, might be able to describe images they claim are invisible. Usually one of four quadrants in the visual field is affected by blindsight.
When patients under the effects of anesthesia listened to recordings through headphones, they were later able to correctly guess words heard while unconscious when given the first three letters. These patients were more apt to compose a word repeated during surgery than other words starting with the same letters. Similar results occurred after testing patients suffering from prosopagnosia syndrome, a disorder that prevents recognition of familiar faces. If given a choice between two options, these patients guessed the correct name more often.
One of the most famous case of subliminal stimuli surfaced in 1957, when market researcher James Vicary claimed he flashed subliminal messages during a movie at a drive-in theater. These stimuli lasted 3/1,000th of a second and were repeated every five seconds, urging people to buy popcorn and drink a certain cola beverage. The psychologist claimed sales of both products rose after the subliminal stimuli.
Details of the study were not released, and no independent evidence supported the claims. Vicary later admitted he falsified the study. Other researchers attempted to duplicate the study with mixed results. A British psychologist found in 1970 that people could identify a string of words interspersed with nonsensical words because the mind perceived information unconsciously.
During this same time, another claim was proven false. Researcher Wilson Bryan Key wrote books claiming the word sex was imbedded in advertising and product packaging that unconsciously spurred sexual arousal and caused people to buy the products. Further studies failed to support the theory that words, objects, or pictures used as subliminal stimuli influenced customer purchasing behavior.
Some respected scientists say self-help tapes with hidden subliminal messages prove ineffective to cure bad habits or enhance weight loss. These tapes remain popular as possible solutions to problems because so many people believe in the power of subliminal stimuli. Some experts believe hidden messages do not even exist on these tape recordings.