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From oral to moral? Dirty deeds may prompt “bad taste” reaction

Feb. 27, 2009
Courtesy Uni­ver­s­ity of To­ron­to/Kim Luke
and World Science staff

When peo­ple say im­mor­al be­hav­iours “leave a bad taste in your mouth,” that may be more than a met­a­phor, some psy­chol­o­gists say. 

A new study sug­gests mor­al dis­gust trig­gers a phys­i­cal re­ac­tion much like the one bad tastes pro­voke, and thus may be linked to old­er forms of re­vul­sion re­lat­ed to poi­son and dis­ease.

Our “sense of what is right and wrong may de­vel­op from a new­born’s in­nate pref­er­ence for what tastes good and bad—what is po­ten­tially nu­tri­tious ver­sus poi­sonous,” said prin­ci­pal in­ves­ti­ga­tor Ad­am An­der­son of the Uni­ver­s­ity of To­ron­to.

Dis­gust is an an­cient emo­tion that “played a key ev­o­lu­tion­ary role” in our an­ces­tors’ sur­viv­al, added Hanah Chap­man, a grad­u­ate stu­dent at the uni­ver­s­ity. She is the lead au­thor of the stu­dy, pub­lished in the Feb. 27 is­sue of the re­search jour­nal Sci­ence

“Our re­search shows the in­volve­ment of dis­gust in mor­al­ity, sug­gest­ing that mor­al judg­ment may de­pend as much on sim­ple emo­tional pro­cesses as on com­plex thought,” she con­tin­ued. “These re­sults shed new light on the ori­gins of mor­al­ity, sug­gest­ing that not only do com­plex thoughts guide our mor­al com­pass, but al­so more prim­i­tive in­stincts.”

The re­search­ers ex­am­ined fa­cial move­ments when study par­ti­ci­pants tast­ed un­pleas­ant liq­uids and looked at pho­tos of dis­gusting ob­jects such as dirty toi­lets or in­ju­ries. They com­pared these to fa­cial move­ments when par­ti­ci­pants suf­fered un­fair treat­ment in a lab­o­r­a­to­ry game. The sci­en­tists found si­m­i­lar­i­ties in the ex­pres­sions.

The psy­chol­o­gists placed small elec­trodes on peo­ple’s faces to de­tect elec­tri­cal ac­ti­vity as­so­ci­at­ed with mus­cle move­ments. They fo­cused on mo­tion of the le­va­tor labii mus­cle, which raises the up­per lip and wrin­kles the nose in “dis­gust.”

“Peo­ple show ac­tiva­t­ion of this mus­cle re­gion in all three situa­t­ions – when tast­ing some­thing bad, look­ing at some­thing dis­gusting and ex­pe­ri­enc­ing un­fair­ness,” said Chap­man. 


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When people say immoral behaviours “leave a bad taste in your mouth,” that may be more than a metaphor, some psychologists say. A new study suggests moral disgust triggers a physical reaction much like the one bad tastes provoke, and thus may be linked to older forms of revulsion related to poison and disease. Our “sense of what is right and wrong may develop from a newborn’s innate preference for what tastes good and bad—what is potentially nutritious versus poisonous,” said principal investigator Adam Anderson of the University of Toronto. Disgust is an ancient emotion that “played a key evolutionary role” in our ancestors’ survival, added Hanah Chapman, a graduate student at the university and lead author of the study, published in the Feb. 27 issue of the research journal Science. “Our research shows the involvement of disgust in morality, suggesting that moral judgment may depend as much on simple emotional processes as on complex thought,” she continued. “These results shed new light on the origins of morality, suggesting that not only do complex thoughts guide our moral compass, but also more primitive instincts.” The researchers examined facial movements when study participants tasted unpleasant liquids and looked at photos of disgusting objects such as dirty toilets or injuries. They compared these to facial movements when participants suffered unfair treatment in a laboratory game. The scientists found similarities in the expressions. The psychologists placed small electrodes on people’s faces to detect electrical activity associated with muscle movements. They focused on motion of the levator labii muscle, which raises the upper lip and wrinkles the nose in “disgust.” “People show activation of this muscle region in all three situations – when tasting something bad, looking at something disgusting and experiencing unfairness,” said Chapman.