Human faces show only four emotions: study

For many years, scientists believed there were six universal facial expressions – happiness, sadness, fear, anger, surprise and disgust.

But researchers at the University of Glasgow have reduced the list to four, after deciding that fear and surprise could be combined because they both cause wide eyes, while anger and disgust make us wrinkle our noses in a similar way.

The researchers used new software to measure the activation of specific face muscles when different emotions were felt.

The Generative Face Grammar platform takes a 3D image of the faces of people trained to activate all 42 facial muscles.

The researchers used those images to computer-generate facial expressions on a 3D model, and asked volunteers to say which emotion was being expressed.

The researchers quickly realised the volunteers confused the expressions of fear and surprise, as well as anger and disgust.

"Our results are consistent with evolutionary predictions, where signals are designed by both biological and social evolutionary pressures to optimise their function," lead researcher Dr Rachael Jack said.

"First, early danger signals confer the best advantages to others by enabling the fastest escape. Secondly, physiological advantages for the expresser – the wrinkled nose prevents inspiration of potentially harmful particles, whereas widened eyes increases intake of visual information useful for escape – are enhanced when the face movements are made early."

Dr Jack said facial expressions appear to have changed over time and in different cultures and plans to do further study.

"As humans migrated across the globe, socio-ecological diversity probably further specialised once-common facial expressions, altering the number, variety and form of signals across cultures," she said.

Dr Bob Wong, a behavioural ecologist at Monash University, told ninemsn the results were interesting and could have relevance for conditions such as autism, where people have difficulty reading communication cues.

"Signalling for communication is important across all animal species," he said.

"It's vital to be able to get those signals conveyed accurately. A lot of these things can be subconscious. We don't necessarily think about it when we talk to people."

But Dr Wong said communication is about more than just expression.

"These researchers only looked at facial expression but we look at a whole bunch of things to determine whether a person is angry or sad," he said.

"You don't want to make the mistake of interpreting someone as angry when they are actually happy."

But Dr Wong said it's difficult for individuals to try to manipulate their facial expressions.

"If you are disgusted by what someone is saying it's often hard to hide that emotion," he says.

The study was published in Current Biology.

Source: BBC Author: Kimberly Gillan, Approving editor: Rory Kinsella