Halloween Café: Ewww Disgusting! The Evolution and Neuroscience of Getting Grossed Out

Karli Carston
Institution of Cognitive Science
Science Discovery Teen Science Café


icsbanner960This café came just in time for halloween! Each of us has felt disgust in specific instances and to different degrees, but why? For example, some people may be able to eat a bowl of salsa with a sterilized tampon dipped into it, whereas other might feel repulsed at just the thought. Why does emotion overtake logic in these cases? Why are some people disgusted more easily than others? For our Halloween Teen Science Café, Dr. Karli Carston from the Institute of Cognitive Science came in to answer these questions and discuss the nature of disgust.
First we looked at the insular cortex, the part of the brain primarily involved in disgust. We viewed various fMRIs of the brain to examine the activity in response to strong sensory input meant to evoke disgust. We then studied images of people’s faces in response to different stimuli meant to trigger emotions such as disgust, fear, and surprise. Dr. Carston explained that when humans encounter disgust, they tend to close off the openings on their faces to limit sensory input, which is displayed by scrunching of the nose, squinting of the eyes, and tightening of the mouth. In contrast, when humans are surprised or afraid, they tend to open their eyes, widen their mouths, and stretch their faces in order to take in more sensory input.

Dr. Carston then talked about learned disgust and inherent disgust as well as what factors can account for differences in disgust reactions from person to person. Specifically, she explained that sometimes we can learn to be disgusted by our social interactions and the way we were raised. For example, when younger children observe others reacting with disgust towards something such as broccoli, they are more likely to mimic that reaction to match societal norms even if they do not feel a strong negative reaction themselves. In addition, some people’s disgust towards certain foods can be rooted in genetics. As an example, some people might have more of a certain taste receptor, thereby making them more sensitive to specific strong foods like kale. Dr. Carston explained that kale actually contains a low concentration of a poisonous ingredient, and that its bitter taste is meant to evoke disgust for safety.

Hands on Activity

We had three stations, each meant to evoke disgust while focusing on a specific sense. Participants chose a partner to record the other’s facial expressions.

  1. The first station involved tasting weird flavor combinations, including chocolate pudding mixed with tuna, Oreos dissolved in orange juice, pickle and peanut butter sandwiches, and Doritos with PB&J. While everyone’s reactions varied for each of the foods, almost all participants had a very strong negative reaction to the chocolate pudding mixed with tuna. In addition, there was a bottle of jelly beans, containing good flavors (watermelon, apple, etc.) mixed with disgusting flavors (vomit, boogers, and soap.) Dr. Carston mentioned that, sometimes, if the participant knows how they are supposed to react, they are more likely to give an exaggerated reaction. Thus, mixing good and bad jellybeans ensured that the participant did not know what to expect (unlike the other foods) and helped control for this effect.
  2. At the second station, participants stuck their hands into a big box with three bowls inside. Each bowl held a substance with a unique texture. The participant did not know what was in the box and did not look inside as they felt around. One bowl contained peeled grapes that had been soaking in water, another had cold spaghetti, and the third was filled with Oobleck, a gelatinous substance. Overall, the reactions to the unique textures were less intense than those to unlikely flavor combinations.
  3. At the last station, participants took a survey and ranked their disgust on a scale of 1 (least disgusted) to 10 (most disgusted) in accordance to specific prompts (e.g. sharing a water bottle). They then summed up their scores and graphed them on a large sheet of paper in relation to their political beliefs. Dr. Carston mentioned that conservatives tend to be more easily and strongly disgusted than liberals because they tend to stick to traditions. Since Boulder is predominantly liberal, we were not able to see a clear trend reflected in our data.

At the end of the café we reconvened to watch some of the slow motion videos capturing people’s facial expressions of disgust for a good laugh and for the purpose of analyzing the similarities and differences in their responses.