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Disgust is a type of aversive reaction that involves withdrawing from a being or object with strong expressions of revulsion. It can also be defined as a revulsion response towards potential contamination. It is a universal, basic emotion that functions to help protect an organism from ingesting potentially harmful substances, thereby promoting disease avoidance. It is one of the basic emotions and is typically associated with things that are regarded as unclean, inedible, infectious, gory or otherwise offensive.
In The Expression of the Emotions in Man and Animals, Charles Darwin wrote that disgust refers to something revolting. Disgust is experienced primarily in relation to the sense of taste (either perceived or imagined), and secondarily to anything which causes a similar feeling by sense of smell, touch, or vision. Musically sensitive people may even be disgusted by the cacophony of inharmonious sounds. Research continually has proven a relationship between disgust and anxiety disorders such as spider phobia, blood-injection-injury phobia, and contamination fear related obsessive-compulsive disorder(also known as OCD).
Disgust is one of the basic emotions of Robert Plutchik's theory of emotions and has been studied extensively by Paul Rozin. It invokes a characteristic facial expression, one of Paul Ekman's six universal facial expressions of emotion. Unlike the emotions of fear, anger, and sadness, disgust is associated with a decrease in heart rate.
It is believed that the emotion of disgust has evolved as a response to offensive foods that may cause harm to the organism. A common example of this is found in human beings who show disgust reactions to mouldy milk or contaminated meat. Many researchers have claimed that the emotion of disgust functions to protect us from disease. Disgust appears to be triggered by objects or people who possess particular types of features that signify disease.
Self-report and behavioural studies found that disgust elicitors include:
The above-mentioned main disgust stimuli are similar to one another in the sense that they can all potentially transmit infections, and are the most common referenced elicitors of disgust cross-culturally. Because of this, disgust is believed to have evolved as a component of a behavioral immune system in which the body attempts to avoid disease-carrying pathogens as opposed to having to fight them after they have entered the body. This behavioral immune system has been found to make sweeping generalizations because "it is more costly to perceive a sick person as healthy than to perceive a healthy person as sickly". Researchers have found that sensitivity to disgust is negatively correlated to aggression because feelings of disgust typically bring about a need to withdraw while aggression results in a need to approach. This can be explained in terms of each of the types of disgust. For those especially sensitive to moral disgust, they would want to be less aggressive because they want to avoid hurting others. Those especially sensitive to pathogen disgust might be motivated by a desire to avoid the possibility of an open wound on the victim of the aggression; however, for those sensitive to sexual disgust, some sexual object must be present for them to be especially avoidant of aggression. Based on these findings, disgust may be used as an emotional tool to decrease aggression in individuals. Disgust may produce specific autonomic responses, such as reduced blood pressure, lowered heart-rate and decreased skin conductance along with changes in respiratory behaviour.
Research has also found that people who are more sensitive to disgust tend to find their own in-group more attractive and tend to have more negative attitudes toward other groups. This may be explained by assuming that people begin to associate outsiders and foreigners with disease and danger while simultaneously associating health, freedom from disease, and safety with people similar to themselves. Although not a justification by any means, this could be an evolutionary explanation for why some people feel racism. When they see others different from themselves, they have an evolved sense of danger arising from a biological desire to avoid potential pathogens brought on by foreigners.
Taking a further look into hygiene, disgust was the strongest predictor of negative attitudes toward obese individuals. A disgust reaction to obese individuals was also connected with views of moral values.
Tybur et al. outlines three domains of disgust: pathogen disgust, which "motivates the avoidance of infectious microorganisms’; sexual disgust, "which motivates the avoidance of [dangerous] sexual partners and behaviors"; and moral disgust, which motivates people to avoid breaking social norms. Disgust may have an important role in certain forms of morality.
Pathogen disgust arises from a desire to survive and, ultimately, a fear of death. He compares it to a "behavioral immune system" that is the "first line of defense" against potentially deadly agents such as dead bodies, rotting food, and vomit.
Sexual disgust arises from a desire to avoid "biologically costly mates" and a consideration of the consequences of certain reproductive choices. The two primary considerations are intrinsic quality (e.g. body symmetry, facial attractiveness, etc.) and genetic compatibility (e.g. avoidance of inbreeding such as the incest taboo).
Moral disgust "pertains to social transgressions" and includes behaviors such as lying, theft, murder, and rape. Unlike the other two domains, moral disgust "motivates avoidance of social relationships with norm-violating individuals" because those relationships threaten group cohesion.
Women generally report greater disgust than men, especially regarding sexual disgust which have been argued to be consistent with women being more choosy regarding sex for evolutionary reasons.
Sensitivity to disgust rises during pregnancy, along with levels of the hormone progesterone. Scientists have conjectured that pregnancy requires the mother to "dial down" her immune system so that the developing embryo won't be attacked. To protect the mother, this lowered immune system is then compensated by a heightened sense of disgust.
Because disgust is an emotion with physical responses to undesirable or dirty situations, studies have proven there are cardiovascular and respiratory changes while experiencing the emotion of disgust.
As mentioned earlier, women experience disgust more prominently than men. This is reflected in a study about dental phobia. A dental phobia comes from experiencing disgust when thinking about the dentist and all that entails. 4.6% of females compared to 2.7% of men find the dentist disgusting.
In a series of significant studies by Paul Ekman in the 1970s, it was discovered that facial expressions of emotion are not culturally determined, but universal across human cultures and thus biological in origin. The facial expression of disgust was found to be one of these facial expressions. This characteristic facial expression includes slightly narrowed brows, a curled upper lip, wrinkling of the nose and visible protrusions of the tongue, although different elicitors may produce different forms of this expression. It was found that the facial expression of disgust is readily recognizable across cultures. This facial expression is also produced in blind individuals and is correctly interpreted by individuals born deaf. This evidence indicates an innate biological basis for the expression and recognition of disgust. The recognition of disgust is also important among species as it has been found that when an individual sees a conspecific looking disgusted after tasting a particular food, he or she automatically infers that the food is bad and should not be eaten. This evidence suggests that disgust is experienced and recognized almost universally and strongly implicates its evolutionary significance.
The mirror-neuron matching system found in monkeys and humans is a proposed explanation for such recognition, and shows that our internal representation of actions is triggered during the observation of another’s actions. It has been demonstrated that a similar mechanism may apply to emotions. Seeing someone else's facial emotional expressions triggers the neural activity that would relate to our own experience of the same emotion. This points to the universality, as well as survival value of the emotion of disgust.
At a very young age, children are able to identify different, basic facial emotions. If a parent makes a negative face and a positive emotional face toward two different toys, a child as young as five months would avoid the toy associated with a negative face. Young children tend to associate a face showing disgust with anger instead of being able to identify the difference. Adults, however, are able to make the distinction. The age of understanding seems to be around ten years old.
Because disgust is partially a result of social conditioning, there are differences among different cultures in the objects of disgust. Americans "are more likely to link feelings of disgust to actions that limit a person’s rights or degrade a person’s dignity" while Japanese people "are more likely to link feelings of disgust to actions that frustrate their integration into the social world". Another contrasting example is with Manchu mothers, who used to show affection for their children by performing fellatio on their male babies since it was not considered a sexual act, while the Manchu regarded public kissing with revulsion, which was considered sexual.
Disgust is one of the basic emotions recognizable across multiple cultures and is a response to something revolting typically involving taste or sight. Though different cultures find different things disgusting, the reaction to the grotesque things remains the same throughout each culture; people and their emotional reactions in the realm of disgust remain the same.
The scientific attempts to map specific emotions onto underlying neural substrates dates back to the first half of the 20th century. However, it was not until the mid-1990s when it was recognized that six basic emotions, including disgust, were each related to a specific neural structure and therefore considered to be a part of the clinical neurosciences. Functional MRI experiments have revealed that the anterior insula in the brain is particularly active when experiencing disgust, when being exposed to offensive tastes, and when viewing facial expressions of disgust. The research has supported that there are independent neural systems in the brain, each handling a specific basic emotion. Specifically, f-MRI studies have provided evidence for the activation of the insula in disgust recognition, as well as visceral changes in disgust reactions such as the feeling of nausea. The importance of disgust recognition and the visceral reaction of "feeling disgusted" is evident when considering the survival of organisms, and the evolutionary benefit of avoiding contamination.
The insula (or insular cortex), is the main neural structure involved in the emotion of disgust. The insula has been shown by several studies to be the main neural correlate of the feeling of disgust both in humans and in macaque monkeys. The insula is activated by unpleasant tastes, smells, and the visual recognition of disgust in conspecific organisms.
The anterior insula is an olfactory and gustatory center that controls visceral sensations and the related autonomic responses. It also receives visual information from the anterior portion of the ventral superior temporal cortex, where cells have been found to respond to the sight of faces.
The fact that the insula is necessary for our ability to feel and recognize the emotion of disgust is further supported by neuropsychological studies. Both Calder (2000) and Adolphs (2003) showed that lesions on the anterior insula lead to deficits in the experience of disgust and recognizing facial expressions of disgust in others. The patients also reported having reduced sensations of disgust themselves. Furthermore, electrical stimulation of the anterior insula conducted during neurosurgery triggered nausea, the feeling of wanting to throw up and uneasiness in the stomach. Finally, electrically stimulating the anterior insula through implanted electrodes produced sensations in the throat and mouth that were "difficult to stand". These findings demonstrate the role of the insula in transforming unpleasant sensory input into physiological reactions, and the associated feeling of disgust.
In a study by Stark & colleagues (2007), sixty-six participants took part in an event-related fMRI analysis. 50 pictures were presented for four seconds and participants rated each picture on the dimensions disgust and fear. The results indicated that both fear and disgust stimulus categories resulted in activations in the occipital cortex, prefrontal cortex and in the amygdala. However, insula activation was only significantly correlated with ratings of disgust, pointing to a specific role of this brain structure in the processing of disgust. In another intensive fMRI study by Wicker & colleagues (2003), disgust reactions to visual and olfactory stimuli were compared. The study consisted of four runs and in the visual runs participants viewed movies of individuals smelling the contents of a glass (conditions: disgusting, pleasant, or neutral) and expressing the facial expressions of the respective emotions. In the olfactory runs, the same participants inhaled disgusting or pleasant odorants. It was found that the anterior insula was activated in both the observation of disgusted facial expressions (visual condition) and during the emotion of disgust evoked by unpleasant odors (olfactory condition). These findings demonstrate that observing someone else's facial expression of disgust seems to automatically retrieve a neural representation of disgust. Furthermore they emphasize the role of the insula in feelings of disgust across the senses.
One particular neuropsychological study focused on patient NK who was diagnosed a left hemisphere infarction involving the insula, internal capsule, putamen and globus pallidus. NK’s neural damage included the insula and putamen and it was found that NK’s overall response to disgust-inducing stimuli was significantly lower than that of controls. The patient showed a reduction in disgust-response on eight categories including food, animals, body products, envelope violation and death. Moreover, NK incorrectly categorized disgust facial expressions as anger. The results of this study support the idea that NK suffered damage to a system involved in recognizing social signals of disgust, due to a damaged insula caused by neurdegeneration.
Many patients suffering from Huntington's disease, a genetically transmitted progressive neurodegenerative disease, are unable to recognize expressions of disgust in others and also don't show reactions of disgust to foul odors or tastes. The inability to recognize expressions of disgust appears in carriers of the Huntington gene before other symptoms appear. People with Huntington's disease are impaired at recognition of anger and fear, and experience a notably severe problem with disgust recognition.
The emotion of disgust may have an important role in understanding the neurobiology of obsessive-compulsive disorder (OCD), particularly in those with contamination preoccupations. In a study by Shapira & colleagues (2003), eight OCD subjects with contamination preoccupations and eight healthy volunteers viewed pictures from the International Affective Picture System during f-MRI scans. OCD subjects showed significantly greater neural responses to disgust-invoking images, specifically in the right insula. Furthermore, Sprengelmeyer (1997) found that the brain activation associated with disgust included the insula and part of the gustatory cortex that processes unpleasant tastes and smells. OCD subjects and healthy volunteers showed activation patterns in response to disgust pictures that differed significantly at the right insula. In contrast, the two groups were similar in their response to threat-inducing pictures, with no significant group differences at any site.
With respect to studies using rats, prior research of signs of a conditioned disgust response have been experimentally verified by Grill and Norgren (1978) who developed a systematic test to assess palatability. The Taste Reactivity (TR) test has thus become a standard tool in measuring disgust response. When given a stimulus intraorally which had been previously paired with a nausea-inducing substance, rats will show conditioned disgust reactions. "Gaping" in rats is the most dominant conditioned disgust reaction and the muscles used in this response mimic those used in species capable of vomiting. Recent studies have shown that treatments that reduced serotonin availability or that activate the endocannibinoid system can interfere with the expression of a conditioned disgust reaction in rats. These researchers showed that as nausea produced conditioned disgust reactions, by administering the rats with an antinausea treatment they could prevent toxin-induced conditioned disgust reactions. Furthermore, in looking at the different disgust and vomiting reactions between rats and shrews the authors showed that these reactions (particularly vomiting) play a crucial role in the associative processes that govern food selection across species. In discussing specific neural locations of disgust, research has shown that forebrain mechanisms are necessary for rats to acquire conditioned disgust for a specific emetic (vomit-inducing) substance (such as lithium chloride). Other studies have shown that lesions to the area postrema and the parabrachial nucleus of the pons but not the nucleus of the solitary tract prevented conditioned disgust. Moreover, lesions of the dorsal and medial raphe nuclei (depleting forebrain serotonin) prevented the establishment of lithium chloride-induced conditioned disgust.
Although disgust was first thought to be a motivation for humans to only physical contaminants, it has since been expanded to apply to moral and social moral contaminants as well. The similarities between these types of disgust can especially be seen in the way people react to the contaminants. For example, if someone stumbles upon a pool of vomit, he/she will do whatever possible to put as much distance between himself/herself and the vomit as possible, which can include pinching the nose, closing the eyes, or running away. Similarly, when a group experiences someone who cheats, murders, or rapes another member of the group, its reaction is to shun or expel that person from the group.
Jones & Fitness (2008) coined the term "moral hypervigilance" to describe the phenomenon that individuals who are prone to physical disgust will also be prone to moral disgust. The link between physical disgust and moral disgust in the United States can especially be seen in the fact that our culture often refers to criminals as "slime" and criminal activity as "stinking" or being "fishy". Furthermore, people often try to block out the stimuli of morally repulsive images in much the same way that they would block out the stimuli of a physically repulsive image. When people see an image of rape or murder, they often turn their heads away to inhibit the incoming visual stimuli from the photograph just like they would if they saw a decomposing body.
Moral judgments can be traditionally defined or thought of as directed by standards such as impartiality and respect towards others for their well-being. From more recent theoretical and empirical information, it can be suggested that morality may be guided by basic affective processes. Jonathan Haidt proposed that one’s instant judgments about morality are experienced as a "flash of intuition" and that these affective perceptions operate rapidly, associatively, and outside of consciousness. From this, moral intuitions are believed to be stimulated prior to conscious moral cognitions which correlates with having a greater influence on moral judgments.
Research suggests that the experience of disgust intensifies the severity of moral judgments. For example, one discovery is that induced disgust results in a more severe moral judgment, even concerning non-moral behaviors, such as choosing discussion topics. However, the experimental effects demonstrated thus far have been rather minor, showing only a slight shift in the severity of the same type of moral judgment.
The effect also seems to be limited to a certain aspect of morality. Horberg et al. found that disgust plays a role in the development and intensification of moral judgments of purity in particular. In other words, the feeling of disgust is often associated with a feeling that some image of what is pure has been violated. For example, a vegetarian might feel disgust after seeing another person eating meat because he/she has a view of vegetarianism as the pure state-of-being. When this state-of-being is violated, the vegetarian feels disgust. Furthermore, disgust appears to be uniquely associated with purity judgments, not with what is just/unjust or what is harmful/caregiving, while other emotions such as fear, anger, and sadness are "unrelated to moral judgments of purity".
Some other research suggests that an individual’s level of disgust sensitivity is due to their particular experience of disgust. One’s disgust sensitivity can be either high or low. The higher one’s disgust sensitivity is means that there is a greater tendency for one to make a stricter moral judgment. Disgust sensitivity can also relate to various aspects of moral values, which can have a negative or positive impact. For example, Disgust sensitivity is associated with moral hypervigilance, which means people who have higher disgust sensitivity are more likely to think that other people who are suspects of a crime are more guilty. They also associate them as being morally evil and criminal, thus endorsing them to harsher punishment in the setting of a court.
Disgust is also theorized as an evaluative emotion that can control moral behavior. When one experiences disgust, this emotion might signal that certain behaviors, objects, or people are to be avoided in order to preserve their purity. Research has established that when the idea or concept of cleanliness is made salient then people make less severe moral judgments of others. From this particular finding, it can be suggested that this reduces the experience of disgust and the ensuing threat of psychological impurity diminishes the apparent severity of moral transgressions.
Although limited research has been done on self-disgust, one study found that self-disgust and severity of moral judgments were negatively correlated. This is in contrast to findings related to disgust, which typically results in harsher judgments of transgressions. This implies that disgust directed towards the self functions very differently from disgust directed towards other people or objects. Self-disgust "may reflect a pervasive condition of self-loathing that makes it difficult to assign deserving punishment to others". In other words, those who feel self-disgust cannot easily condemn others to punishment because they feel that they may also be deserving of punishment.
The emotion of disgust can be described to serve as an affective mechanism following occurrences of negative social value, provoking repulsion, and desire for social distance. The origin of disgust can be defined by motivating the avoidance of offensive things, and in the context of a social environment, it can become an instrument of social avoidance. An example of disgust in action can be found from the Bible in the book of Leviticus. Leviticus includes direct commandments from God to avoid disgust causing individuals, which included people who were sexually immoral and those who had leprosy. Disgust is also known to have originally evolved as a response to unpleasant food that may have been carriers of disease. As an affective instrument for reducing motivations for social interaction, disgust can be anticipated to interfere with dehumanization or the maltreatment of persons as less than human. Research was performed which conducted several functional magnetic resonance images (fMRI) in which participants viewed images of individuals from stigmatized groups that were associated with disgust, which were drug addicts and homeless people. What the study found was that people were not inclined in making inferences about the mental conditions of these particular disgust inducing groups. Therefore, examining images of homeless people and drug addicts caused disgust in the response of the people who participated with this study. This study coincides with disgust following the law of contagion, which explains that contact with disgusting material renders one disgusting. Disgust can be applied towards people and can function as maltreatment towards another human being. Disgust can exclude people from being a part of the inner circle by leading to the view that they are merely less than human. An example of this is if groups were to avoid people from outside of their own particular group. Some researchers have distinguished between two different forms of dehumanization. The first form is the denial of uniquely human traits, examples include: products of culture and modification. The second form is the denial of human nature, examples include: emotionality and personality. Failure to attribute distinctively human traits to a group leads to animalistic dehumanization, which defines the object group or individual as savage, crude, and similar to animals. These forms of dehumanization have clear connections to disgust. Researchers have proposed that many disgust elicitors are disgusting because they are reminders that humans are not diverse from other creatures. With the aid of disgust, animalistic dehumanization directly reduces one’s moral concerns towards excluding members from the outer group. Disgust can be a cause and consequence of dehumanization. Animalistic dehumanization may generate feelings of disgust and revulsion. Feelings of disgust, through rousing social distance, may lead to dehumanization. Therefore, a person or group that is generally connected with disgusting effects and seen as physically unclean may induce moral avoidance. Being deemed disgusting produces a variety of cognitive effects that result in exclusion from the perceived inner group.
The emotion disgust has been noted to feature strongly in the public sphere in relation to issues and debates, among other things, regarding anatomy, sex and bioethics. There is a range of views by different commentators on the role, purpose and effects of disgust on public discourse.
Leon Kass, a bioethicist, has advocated that "in crucial cases...repugnance is the emotional expression of deep wisdom, beyond reason's power fully to articulate it." in relation to bio-ethical issues (See: Wisdom of repugnance).
Martha Nussbaum, a jurist and ethicist, explicitly rejects disgust as an appropriate guide for legislating, arguing the "politics of disgust" is an unreliable emotional reaction with no inherent wisdom. Furthermore she argues this "politics of disgust" has in the past and present had the effects of supporting bigotry in the forms of sexism, racism and antisemitism and links the emotion of disgust to support for laws against Miscegenation and the oppressive caste system in India. In place of this "politics of disgust", Nussbaum argues for the Harm principle from John Stuart Mill as the proper basis for legislating. Nussbaum argues the harm principle supports the legal ideas of consent, the Age of majority and privacy and protects citizens. She contrasts this with the "politics of disgust" which she argues denies citizens humanity and equality before the law on no rational grounds and cause palpable social harm. (See Martha Nussbaum, From Disgust to Humanity: Sexual Orientation and Constitutional Law). Nussbaum published Hiding From Humanity: Disgust, Shame, and the Law in 2004; the book examines the relationship of disgust and shame to a society's laws. Nussbaum identifies disgust as a marker that bigoted, and often merely majoritarian, discourse employs to "place", by diminishment and denigration, a despised minority. Removing "disgust" from public discourse constitutes an important step in achieving humane and tolerant democracies.
Leigh Turner (2004) has argued that "reactions of disgust are often built upon prejudices that should be challenged and rebutted." On the other hand, writers, such as Kass, find wisdom in adhering to one's initial feelings of disgust. A number of writers on the theory of disgust find it to be the proto-legal foundation of human law.
Disgust has also figured prominently in the work of several other philosophers. Nietzsche became disgusted with the music and orientation of Richard Wagner, as well as other aspects of 19th century culture and morality. Jean-Paul Sartre wrote widely about experiences involving various negative emotions related to disgust.
According to the book The Hydra’s Tale: Imagining Disgust by Robert Rawdon Wilson, disgust may be further subdivided into physical disgust, associated with physical or metaphorical uncleanliness, and moral disgust, a similar feeling related to courses of action. For example; "I am disgusted by the hurtful things that you are saying." Moral disgust should be understood as culturally determined; physical disgust as more universally grounded. The book also discusses moral disgust as an aspect of the representation of disgust. Wilson does this in two ways. First, he discusses representations of disgust in literature, film and fine art. Since there are characteristic facial expressions (the clenched nostrils, the pursed lips), as Charles Darwin, Paul Ekman and others have shown, they may be represented with more or less skill in any set of circumstances imaginable. There may even be "disgust worlds" in which disgust motifs so dominate that it may seem that entire represented world is, in itself, disgusting. Second, since people know what disgust is as a primary, or visceral, emotion (with characteristic gestures and expressions), they may imitate it. Thus, Wilson argues, contempt is, for example, acted out on the basis of the visceral emotion, disgust, but is not identical with disgust. It is a "compound affect" that entails intellectual preparation, or formatting, and theatrical techniques. Wilson argues that there are many such "intellectual" compound affects, such as nostalgia and outrage, but that disgust is a fundamental and unmistakable example. Moral disgust, then, is different from visceral disgust, more conscious and more layered in performance.
Wilson links shame and guilt to disgust (now transformed, wholly or partially, into self-disgust) primarily as a consequence rooted in self-consciousness. Referring to a passage in Doris Lessing’s The Golden Notebook, Wilson writes that ". . . the dance between disgust and shame takes place. A slow choreography unfolds before the mind’s-eye." 
Wilson examines the claims of several jurists and legal scholars, such as William Ian Miller, that disgust must underlie positive law. "In the absence of disgust," he observes, stating their claim,". . . there would be either total barbarism or a society ruled solely by force, violence and terror." The moral-legal argument, he remarks, "leaves much out of account." His own argument turns largely upon the human capacity to learn how to control, even to suppress, strong and problematic affects and, over time, for entire populations to abandon specific disgust responses.
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