It is a commonly-held belief that humans express six basic emotions which are universally recognized and easily interpreted through specific facial expressions, regardless of language or culture. These are
However, a new research by scientists at the University of Glasgow has challenged this view, and suggested that there are only four basic emotions.
Their conclusion was reached by studying the range of different muscles within the face - or Action Units as researchers refer to them - involved in signalling different emotions, as well as the time-frame over which each muscle was activated.
This is the first such study to objectively examine the 'temporal dynamics' of facial expressions, made possible by using a unique Generative Face Grammar platform developed at the University of Glasgow.
The team from the Institute of Neuroscience and Psychology claim that while the facial expression signals of happiness and sadness are clearly distinct across time, fear and surprise share a common signal - the wide open eyes - early in the signalling dynamics.
Similarly, anger and disgust share the wrinkled nose. It is these early signals that could represent more basic danger signals. Later in the signalling dynamics, facial expressions transmit signals that distinguish all six 'classic' facial expressions of emotion.
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Lead researcher Dr Rachael Jack said that their research shows that 'basic' facial expression signals are perceptually segmented across time and follow an evolving hierarchy of signals over time - from the biologically-rooted basic signals to more complex socially-specific signals.
The study was published in the journal Current Biology.