Subliminal stimuli (; the prefix ' literally means "below" or "less than") are any sensory
stimuli A stimulus is something that causes a physiological response. It may refer to: *Stimulation Stimulation is the encouragement of development or the cause of activity generally. For example, "The press provides stimulation of political discourse." ...
below an individual's threshold for conscious
perception Perception (from the Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" o ...

, in contrast to stimuli (above threshold). A 2012 review of
functional magnetic resonance imaging Functional magnetic resonance imaging or functional MRI (fMRI) measures brain activity by detecting changes associated with blood flow Hemodynamics American and British English spelling differences#ae and oe, or haemodynamics are the Fluid dynami ...

functional magnetic resonance imaging
(fMRI) studies showed that subliminal stimuli activate specific regions of the brain despite participants' unawareness. Visual stimuli may be quickly flashed before an individual can process them, or flashed and then masked to interrupt processing. Audio stimuli may be played below audible volumes or masked by other stimuli.


Applications of subliminal
stimuli A stimulus is something that causes a physiological response. It may refer to: *Stimulation Stimulation is the encouragement of development or the cause of activity generally. For example, "The press provides stimulation of political discourse." ...
are often based on the
persuasive Persuasion or persuasion arts is an umbrella term of influence Influence or influencer may refer to: *Social influence, in social psychology, influence in interpersonal relationships **Minority influence, when the minority affect the behavior ...
ness of a message. Research on action priming has shown that subliminal stimuli can only trigger actions a receiver of the message plans to perform anyway. However, consensus of subliminal messaging remains unsubstantiated by other research. Most actions can be triggered subliminally only if the person is already prepared to perform a specific action. The context that the stimulus is presented in affects their effectiveness. For example, if the target is thirsty then a subliminal stimuli for a drink is likely to influence the target to purchase that drink if it is readily available. The stimuli can also influence the target to choose the primed option over other habitually chosen options. If the subliminal stimuli is for a product that is not quickly accessible or if there is no need for it within a specific context then the stimuli will have little to no effect. Subliminal priming can direct people's actions even when they believe they are making free choices. When primed to push a button with their off-hand, people will use that hand even if they are given a free choice between using their off-hand and their dominant hand. However, a meta analysis of many strong articles displaying effectiveness of subliminal messaging revealed its effects on actual consumer purchasing choices between two alternatives are not statistically significant; subliminal messaging is only effective in very specific contexts.


In subliminal stimuli research, the threshold is the level at which the participant is not aware of the stimulus being presented. Researchers determine a threshold for the stimulus that is used as the subliminal stimulus. That stimulus is then presented during the study at some point and measures are taken to determine the effects of the stimulus. The way in which studies operationally define thresholds depends on the methods of the particular article. The methodology of the research also varies by the type of subliminal stimulus (auditory or visual) and the
dependent variable Dependent and Independent variables are variables in mathematical modeling, statistical modeling and experimental sciences. Dependent variables receive this name because, in an experiment, their values are studied under the supposition or demand ...
s they measure.

Objective threshold

The objective threshold is found using a forced-choice procedure, in which participants must choose which stimulus they saw from options given to them. For example, participants are flashed a stimulus (like the word ''orange'') and then given a few choices and asked which one they saw. Participants must choose an answer in this design. The objective threshold is obtained when participants are at the chance level of performance in this task. The length of presentation that causes chance performance on the forced-choice task is used later in the study for the subliminal stimuli.

Subjective threshold

The subjective threshold is determined when the participant reports that their performance on the forced-choice procedure approximates chance. The subjective threshold is 30 to 50 ms slower than the objective threshold, demonstrating that participants' ability to detect the stimuli is earlier than their perceived accuracy ratings would indicate; that is, stimuli presented at a subjective threshold have a longer presentation time than those presented at an objective threshold. When using the objective threshold, priming stimuli neither facilitated nor inhibited the recognition of a color. However, the longer the duration of the priming stimulus, the greater effect it had on subsequent responding. These findings indicate that the results of some studies may be due to their definition of below threshold.

Direct and indirect measures

Perception without awareness can be demonstrated through the comparison of direct and indirect measures of perception. Direct measures use responses to task definitions in accordance to the explicit instructions given to the subjects, while indirect measures use responses that are not a part of the task definition given to subjects. Both direct and indirect measures are displayed under comparable conditions except for the direct or indirect instruction. For example, in a typical
Stroop test ---- ---- Naming the font color of a printed word is an easier and quicker task if word meaning and font color are congruent. If two words are both printed in red, the average time to say "red" in response to the written word "green" is g ...

Stroop test
, subjects are asked to name the color of a patch of ink. A direct measure is accuracy—true to the instructions given to the participants. The popular indirect measure used in the same task is response time—subjects are not told that they are being measured for response times. Similarly, a direct effect is the effect of a task stimulus on the instructed response to it, and is usually measured as accuracy. An indirect effect is an uninstructed effect of the task stimulus on behavior, sometimes measured by including an irrelevant or distracting component in the task stimulus and measuring its effect on accuracy. These effects are then compared on their relative sensitivity: an indirect effect that is greater than a direct effect indicates that unconscious cognition exists.

Visual stimuli

In order to study the effects of subliminal stimuli, researchers often prime participants with specific visual stimuli, and determine if those stimuli elicit different responses. Subliminal stimuli have mostly been studied in the context of emotion; in particular, researchers have focused a lot of attention to the face perception and how subliminal presentation to different facial expression affects emotion. Visual subliminal stimuli have also been used to study emotion eliciting stimuli and simple geometric stimuli. A significant amount of research has been produced throughout the years to demonstrate the effects of subliminal visual stimuli.


Attitudes can develop without being aware of their antecedents. Individuals viewed slides of people performing familiar daily activities after being exposed to either an emotionally positive scene, such as a romantic couple or kittens, or an emotionally negative scene, such as a werewolf or a dead body between each slide and the next. After exposure from something which the individuals consciously perceived as a flash of light, the participants exhibited more positive personality traits to those people whose slides were associated with an emotionally positive scene and vice versa. Despite the statistical difference, the subliminal messages had less of an impact on judgment than the slide's inherent level of physical attractiveness. Individuals show right
amygdala The amygdala (; plural: amygdalae or amygdalas; also '; Latin from Greek language, Greek, , ', 'almond', 'tonsil') is one of two almond-shaped clusters of nucleus (neuroanatomy), nuclei located deep and lateral and medial, medially within the ...

activity in response to subliminal fear, and a greater left amygdala response to supraliminal fear. In a 2005 study, participants were exposed to a subliminal image flashed for 16.7 milliseconds that could signal a potential threat and again with a supraliminal image flashed for half a second. Furthermore, supraliminal fear showed more sustained cortical activity, suggesting that subliminal fear may not entail conscious surveillance while supraliminal fear entails higher-order processing.

Emotion eliciting stimuli

A subliminal sexual stimulus has a different effect on men compared to women. In a study by Omri Gilliath ''et al.'', men and women were subliminally exposed to either a sexual or a neutral picture, and their
sexual arousal Sexual arousal (also sexual excitement) describes the physiological Physiology (; ) is the scientific Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone ...
was recorded. Researchers examined the accessibility of sex-related thoughts after following the same procedure with either a pictorial judgment task or
lexical decision taskThe lexical decision task (LDT) is a procedure used in many psychology Psychology is the science of mind and behavior. Psychology includes the study of consciousness, conscious and Unconscious mind, unconscious phenomena, as well as feeling a ...
. The results revealed that the subliminal sexual stimuli did not have an effect on men, but for women, lower levels of sexual arousal were reported. However, in conditions related to accessibility of sex-related thoughts, the subliminal sexual stimuli led to higher accessibility for both men and women. Subliminal stimuli can elicit significant emotional changes, but these changes are not valuable for a
therapeutic effect Therapeutic effect refers to the response(s) after a treatment of any kind, the results of which are judged to be useful or favorable. This is true whether the result was expected, unexpected, or even an unintended consequence. An adverse effect (i ...
. Spider-fearful and non-fearful undergraduates experienced either a positive, negative, or neutral subliminal priming stimulus followed immediately by a picture of a spider or a snake. Using visual analogue scales, the participants rated the affective quality of the picture. No evidence was found to support that the unpleasantness of the pictures can be modulated by subliminal priming. Non-fearful participants rated the spiders as being more frightening after being primed with a negative stimulus, but the event was not found in fearful participants.

Simple geometric stimuli

Laboratory research on unconscious perception often employs simple stimuli (e.g.,
geometric shapes Geometric Shapes is a Unicode block A Unicode block is one of several contiguous ranges of numeric character codes (code point In character encoding terminology, a code point or code position is any of the numerical values that make up the ...

geometric shapes
or colors) in which visibility is controlled by visual masking. Masked stimuli are then used to prime the processing of subsequently presented target stimuli. For instance, in the
response priming In the psychology of perception and motor control, the term response priming denotes a special form of Priming (psychology), priming. Generally, priming effects take place whenever a response to a target stimulus is influenced by a prime Stimulus (p ...
paradigm, participants have to respond to a target stimulus (e.g. by identifying whether it is a diamond or a square) which is immediately preceded by a masked priming stimulus (also a diamond or a square). The prime has large effects on responses to the target: it speeds responses when it is consistent with the target, and slows responses when it is inconsistent. Response priming effects can be dissociated from visual awareness of the prime, such as when prime identification performance is at chance, or when priming effects increase despite decreases in prime visibility. The presentation of geometric figures as subliminal stimuli can result in below threshold discriminations. The geometric figures were presented on slides of a
tachistoscope A tachistoscope is a device that displays an image An SAR radar imaging, radar image acquired by the SIR-C/X-SAR radar on board the Space Shuttle Endeavour shows the Teide volcano. The city of Santa Cruz de Tenerife is visible as the purp ...
followed by a supraliminal shock for a given slide every time it appeared. The shock was administered after a five-second interval. Electrical skin changes of the participants that occurred before the
reinforcement In behavioral psychology Behaviorism is a systematic approach to understanding the behavior of humans and other animals. It assumes that behavior is either a reflex evoked by the pairing of certain antecedent (behavioral psychology), anteced ...

(shock) or non-reinforcement were recorded. The findings indicate that the proportion of electrical skin changes that occurred following subliminal visual stimuli was significantly greater than expected, while the proportion of electrical skin changes that occurred in response to the stimuli which were not reinforced was significantly less. As a whole, participants were able to make below threshold discriminations.

Word and non-word stimuli

Another form of visual stimuli is words and non-words. In a set of experiments, words and non-words were used as subliminal primes. Priming stimuli that work best as subliminal stimuli are words that have been classified several times before they are used to prime. Word primes can also be made from parts of practiced words to create new words. In this case, the actual word used to prime can have the opposite meaning of the words it came from (its "parents"), but it will still prime for the meaning of the parent words. Non-words created from previously practiced stimuli have a similar effect, even when they are unpronounceable (e.g. made of all consonants). These primes generally only increase response times for later stimuli for a very short period of time (milliseconds).

Masking visual stimuli

Visual stimuli are often masked by forward and backward masks so that they can be displayed for longer periods of time without the subject being able to recognize the priming stimuli. A forward mask is briefly displayed before the priming stimulus and a backward mask usually follows it to prevent the subject from recognizing the stimulus.

Auditory stimuli

Auditory masking

One method for creating subliminal auditory stimuli is masking, which involves hiding the target auditory stimulus in some way. Auditory subliminal stimuli are shown to have some effect on the participant, but not a large one. For example, one study used other speechlike sounds to cover up the target words, and it found evidence of priming in the absence of awareness of the stimuli. The effects of these subliminal stimuli were only seen in one of the outcome measures of priming, while the effects of conscious stimuli were seen in multiple outcome measures. However, the empirical evidence for the assumption of an impact of auditory subliminal stimuli on human behavior remains weak; in an experimental study on the influence of subliminal target words (embedded into a music track) on choice behavior for a drink, authors found no evidence for a manipulative effect.

Self-help audio recordings

A study investigated the effects on self-concept of
rational emotive behavior therapy Rational emotive behavior therapy (REBT), previously called rational therapy and rational emotive therapy, is an active-directive, philosophically and empirical Empirical evidence is the information received by means of the senses, particular ...
and auditory subliminal stimulation (separately and in combination) on 141 undergraduate students with self-concept problems. They were randomly assigned to one of four groups receiving either rational-emotive therapy, subliminal stimulation, both, or a placebo treatment. Rational-emotive therapy significantly improved scores on all dependent measures (cognition, self-concept, self-esteem, anxiety) except behavior. Results for the subliminal stimulation group were similar to those of the placebo treatment except for a significant self-concept improvement and a decline in self-concept-related irrational cognitions. The combined treatment yielded results similar to those of rational-emotive therapy, with tentative indications of continued improvement in irrational cognitions and self-concept from posttest to follow-up.

Consumption and television

Some studies looked at the efficacy of subliminal messaging in
television Television, sometimes shortened to TV or telly, is a telecommunication Telecommunication is the transmission of information by various types of technologies over wire A wire is a single usually cylindrical A cylinder (from Gre ...

. Subliminal messages produce only one-tenth of the effects of detected messages and the findings related to the effects of subliminal messaging were relatively ambiguous. Participants’ ratings of positive responses to commercials were not affected by subliminal messages in the commercials. Johan Karremans suggests that subliminal messages have an effect when the messages are goal-relevant. In a study, researchers made half of the 105 volunteers feel thirsty by giving them food with lots of salt before performing the experiment. At the end, as predicted, they found that the subliminal message had succeeded among the thirsty. 80% of them chose "''Lipton Ice''" versus the 20% of the control group that were not exposed to the message. However, those who were not thirsty did not choose the drink in question, despite the subliminal message. The experiment showed that in certain circumstances subliminal advertising worked. Karremans did a study assessing whether subliminal priming of a brand name of a drink would affect a person's choice of drink, and if this effect was caused by the individual's feelings of being thirsty. In another study, participant's ratings of thirst were higher after viewing an episode of ''
The Simpsons ''The Simpsons'' is an American animated sitcom created by Matt Groening for the Fox Broadcasting Company. The series is a satirical depiction of American life, epitomized by the Simpson family, which consists of Homer Simpson, Homer, Marge Si ...
'' that contained single frames of the word ''thirsty'' or of a picture of a Coca-Cola can. Some studies showed greater effects of subliminal messaging with as high as 80% of participants showing a preference for a particular rum when subliminally primed by the name placed in an ad backward.
Martin Gardner Martin Gardner (October 21, 1914May 22, 2010) was an American popular mathematics Popular mathematics is mathematics, mathematical presentation aimed at a general audience. Sometimes this is in the form of books which require no mathematical ba ...
, however, criticizes claims, such as those by
Wilson Bryan Key Wilson Bryan Key Ph.D. (January 31, 1925 – October 8, 2008) was the author of several books about subliminal messages and subliminal advertising. Career Key obtained his doctorate in communications from the University of Denver The Uni ...
, by pointing out that "recent studies" serving as the basis for his claims were not identified by place or experimenter. He also suggests that claims about subliminal images are due to the "tendency of chaotic shapes to form patterns vaguely resembling familiar things". In 2009, the
American Psychological Association The American Psychological Association (APA) is the largest scientific and professional organization of psychologist A psychologist is a professional A professional is a member of a profession or any person who earns a living from a speci ...
defended that subliminal stimuli are subordinated to previously structured associative stimuli and that their only role is to reinforce a certain behavior or a certain previous attitude, without there being conclusive evidence that the stimulus that provokes these behaviors is properly subliminal. Currently, there is still speculation about this effect. Many authors have continued to argue for the effectiveness of subliminal cues in changing consumption behavior, citing environmental cues as a main culprit of behavior change. Authors who support this line of reasoning cite findings such as Ronald Millman's research that showed slow-paced music in a
supermarket A supermarket is a self-service Retail#Types of outlets, shop offering a wide variety of food, Drink, beverages and Household goods, household products, organized into sections. This kind of store is larger and has a wider selection than earli ...

was associated with more sales and customers moving at a slower pace. Findings such as these support the notion that external cues can affect behavior, although the stimulus may not fit into a strict definition of subliminal stimuli because although the music may not be attended to or consciously affecting the customers, they are certainly able to perceive it. Subliminal messaging is prohibited in
advertising Advertising is a marketing Marketing is the process of intentionally stimulating demand for and purchases of goods and services; potentially including selection of a target audience; selection of certain attributes or themes to emphasi ...

in the United Kingdom.

Studies on advertising with subliminal stimuli in still images

Among the researchers in favor of subliminal stimuli is
Wilson Bryan Key Wilson Bryan Key Ph.D. (January 31, 1925 – October 8, 2008) was the author of several books about subliminal messages and subliminal advertising. Career Key obtained his doctorate in communications from the University of Denver The Uni ...
. One of Key's most cited studies is a whisky ad in which he found several hidden figures in ice cubes. However, for other researchers Key is someone with a sexual fixation.Adams, Cecil. ''Are subliminal messages secretly embedded in advertisements?''
/ref> Luís Bassat suggests an interesting observation by indicating that the current objective of advertising is "to get the consumer to take into account the brand when making the decision",Bassat, Luís, ''Libro rojo de la publicidad'', Editorial Planeta, Barcelona, 2003 a trend opposed to the objective of subliminal advertising. In turn, Fernando Ocaña showed that the essential thing in the field of
media planning Media planning is generally outsourced and entails sourcing and selecting optimal media platforms for a client's brand or product to use. The goal of media planning is to determine the best combination of media to achieve the clients objectives. I ...
is to obtain the greatest possible memory, which implies a conscious perception and not an unconscious one as it should be the case.

See also

Instances of subliminal messages These are instances of subliminal messages that have led to controversy and occasionally legal allegations. *In 1978, Wichita, Kansas Wichita ( ) is the largest city in the U.S. state of Kansas and the county seat of Sedgwick County, Kansas, S ...
Subliminal messages in popular culture While the effectiveness of subliminal messages is often overstated in popular culture, its history in television shows, movies, music and novels have long lead many cultural idioms that persist today. Governments are often depicted as employing sub ...
Neuroethics Neuroethics refers to two related fields of study: what the philosopher Adina Roskies has called the ethics of neuroscience, and the neuroscience of ethics. The ethics of neuroscience comprises the bulk of work in neuroethics. It concerns the ethic ...
Peripheral vision horizon displayThe peripheral vision horizon display, also called PVHD or the Malcolm Horizon (after inventor Dr. Richard Malcolm), is an aircraft cockpit A cockpit or flight deck is the area, usually near the front of an aircraft An aircraft is a vehicle ...
(PVHD) * Pre-attentive processing *
Priming (psychology) Priming is a phenomenon whereby exposure to one stimulus A stimulus is something that causes a physiological response. It may refer to: *Stimulation Stimulation is the encouragement of development or the cause of activity generally. For exampl ...
Response priming In the psychology of perception and motor control, the term response priming denotes a special form of Priming (psychology), priming. Generally, priming effects take place whenever a response to a target stimulus is influenced by a prime Stimulus (p ...


Further reading

* * * * * * * {{Cite journal, first1 = T., last1 = Watanabe, first2 = J., first3 = Y., journal = Nature, pages = 844–848 , doi = 10.1038/35101601, last2 = Náñez, volume = 413, last3 = Sasaki, year = 2001, pmid = 11677607, title = Perceptual learning without perception, issue = 6858, s2cid = 4381577 Sensory systems