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Some things are universal and, when it comes to expressing disgust, one facial expression is understood globally.

However, happiness is more complex. There are 17 different facial expressions, a testament to the many varied forms of cheer, delight and contentedness.聽And while humans can聽configure their faces in thousands and thousands of ways to convey emotion, only 35 expressions actually get the job done across cultures, a new study has found.

鈥淭his was delightful to discover,鈥� said聽Aleix Martinez, cognitive scientist, professor of聽electrical and computer engineering聽at The Ohio State University and study co-author, 鈥渂ecause it speaks to the complex nature of happiness.鈥�

The differences in how our faces convey happiness can be as simple as the size of our smiles or the crinkles near our eyes, the study found.

The study, published in聽the journal聽IEEE Transactions on Affective Computing,聽also found that humans use three expressions to convey fear, four to convey surprise, and five each to convey sadness and anger.

鈥淗appiness acts as a social glue and needs the complexity of different facial expressions. Disgust is just that: disgust,鈥� Martinez said.

The findings build on Martinez鈥檚聽previous work on facial expressions, which found that people can correctly identify other people鈥檚 emotions about 75% of the time based solely on subtle shifts in how blood flow colours a person鈥檚 nose, eyebrows, cheeks or chin.

In this study, Martinez and co-author Ramprakash Srinivasan, a doctoral student at Ohio State in Martinez鈥檚 lab, assembled a list of words that describe feelings 鈥� 821 English words, to be exact. They then used those words to mine the internet for images of people鈥檚 faces. Professional translators translated those words into Spanish, Mandarin Chinese, Farsi and Russian. To avoid bias, they used each word to download an equal number of images.

They plugged the words into search engines popular in 31 countries across North America, South America, Europe, Asia and Australia, and ended up with approximately 7.2 million images of facial expressions across a variety of cultures. The study did not include countries from the African continent or other remote parts of the world, due to the limited number of candid images available from those areas.

Psychologists have debated how to classify human emotion for centuries.聽An ancient Chinese text 鈥� dating back as early as 213 BC, then modified over the years 鈥� described seven 鈥渇eelings of men鈥� as joy, anger, sadness, fear, love, disliking and liking.

Martinez, whose research interests intersect both engineering and the behaviour of the human brain, thought there had to be more than just seven or eight.

鈥淭o think that humans are only capable of eight emotions is absurd,鈥� he said. 鈥淲e are complex creatures. What about the different forms of joy? We experience the world on a much deeper level than just eight emotions.鈥�

Martinez and Srinivasan hoped to identify the facial configurations that convey emotion across cultures. Based on computer algorithms, they found that the human face is capable of configuring itself in 16,384 unique ways, combining different muscles in different ways. They took the 7.2 million images their searches yielded and sorted them into categories, looking for those that expressed emotion across cultures. Martinez figured they鈥檇 find at least a few hundred.

They found only 35.

鈥淲e were shocked,鈥� Martinez said. 鈥淚 thought there would be way, way more.鈥�

Since the number of universal expressions was smaller than expected, they wondered if most expressions of emotion were culture-specific. The result of this study surprised them even more. Analysis of the same dataset of 7.2 million images showed there are only eight expressions that are used in some 鈥� but not all 鈥� cultures. These eight expressions convey positive and negative affect, but not emotion categories like joy and anger. The researchers concluded that most facial expressions of emotion are universal, that there are only a few dozen of them and that a large number of them are used to express joyfulness.

Image credit: 漏stock.adobe.com/au/Raisa Kanareva