Psychologists have long been investigating the connection between facial expressions and emotions. A theory first offered by Paul Ekman, says that there are six primary emotions that are globally recognized and easily construed through specific facial expressions: happiness, sadness, fear, anger, surprise and disgust.
According to new research published in the journal Current Biology, scientists at the University of Glasgow have discovered that there are only four basic emotions: happiness, sadness, fear/surprise and anger/disgust.
In a unique approach, the study team looked at the ‘temporal dynamics’ of facial expressions, thanks to a unique system developed at the University of Glasgow. They studied the array of different muscles inside the face involved with conveying different emotions, called ‘Action Units,’ in addition to the time-frame over which each muscle was triggered.
The scientists determined that while the facial expression signals of happiness and sadness are clearly unique across time, fear and surprise share a typical signal — the wide open eyes — at the start of the signaling mechanics. Likewise, anger and disgust share the wrinkled nose.
It is these first signals that could possibly represent simpler danger signals. Later in the signaling mechanics, facial expressions transfer signals that differentiate all six ‘classic’ facial expressions of emotion, the researchers said.
“Our results are consistent with evolutionary predictions, where signals are designed by both biological and social evolutionary pressures to optimize their function,” said study author Rachael Jack, a psychologist at the Scottish university.
“First, early danger signals confer the best advantages to others by enabling the fastest escape,” Jack explained. “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.”
“What our research shows is that not all facial muscles appear simultaneously during facial expressions, but rather develop over time supporting a hierarchical biologically-basic to socially-specific information over time,” she added.
The unique system developed by the study team uses cameras to record a three-dimensional image of participants’ faces. These participants were expressly trained to be able to activate all 42 individual facial muscles separately.
From the image, the system computer could generate a specific or random facial expression on a 3D model based on the triggering of different Action Units or clusters of units to impersonate all facial expressions.
Participants were then asked to observe the computer model as it generated various expressions and determine which emotion was being articulated. The researchers could then tell which specific Action Units observers correlate with specific emotions.
The study team discovered that the signals for fear/surprise and anger/disgust were confused at the beginning stage of transmission and only became more obvious later when other Action Units were incorporated.
“Our research questions the notion that human emotion communication comprises six basic, psychologically irreducible categories. Instead we suggest there are four basic expressions of emotion,” Jack said.