Science: Why Bad Behavior Leaves a "Bad Taste" in the Mouth

Appearance model–generated average facial expressions of the five most expressive individuals (from a total sample of 20) tasting neutral, sweet, and bitter solutions. The upper lip and nose areas are highlighted to show the action of the levator labii muscle (upper lip raise and nose wrinkle) across conditions.

[Image © Science/AAAS]

When another person's behavior leaves you with "a bad taste in the mouth," are you revealing something much more than a colorful metaphor? New research suggests that a nose wrinkled in disgust over a moral shortcoming may have its roots in the bad taste that twists the tongue.

A distasteful drink, a repulsive photo, and unfair treatment in a game all raise the upper lip and wrinkle the nose with the help of a facial muscle called the levator labii, Hanah Chapman, a psychologist at the University of Toronto, and her colleagues report in the 27 February issue of the journal Science.

The muscle sprang to life when participants in the Chapman experiment downed a foul concoction of bitter, salty and sour liquids and looked at photos of "disgusting" objects such as feces and insects. But perhaps more surprisingly, the muscle also went to work when the participants received less money than they expected in a game where they divvied up funds with a partner.

Why would the same muscle produce the same disgusted look in these distinctly different situations? The similarities might indicate that the moral disgust response has its origins in a more ancient evolutionary response to smells, sights and tastes that signal toxins or contamination.

The facial machinery that turns up the nose at a spoiled bite may be "co-opted and expanded to reject offensive stimuli in the social realm," the researchers noted, so that "unfair offers may be received like a plate of spoiled food."

Chapman and colleagues said the Science study joins a growing body of research that suggests some aspects of human morality may have their foundations in older biological and emotional responses, rather than conscious reasoning.

Negative emotions endorsed for $9:$1 offers. Disgust, anger, and sadness expression photographs used in the self-report task were modified using a computer model of facial appearance by weighting the expression intensity by the strength of emotion endorsement; the far right panel shows a composite of these expressions. The upper lip and nose areas are highlighted, showing the action of the levator labii muscle (upper lip raise and nose wrinkle) in the disgust expression and composite.

[Image © Science/AAAS]

Becky Ham

26 February 2009