Dr Korb hopes the research can explore potential treatments for depression or disorders that affect expression, like Parkinson’s and autism.
He said: “The finding that a controlled, brief and weak activation of facial muscles can literally create the illusion of happiness in an otherwise neutral or even slightly sad looking face, is ground-breaking.
“It is relevant for theoretical debates about the role of facial feedback in emotion perception and has potential for future clinical applications.”
Dr Korb used a modernised version of a technique first developed in the 19th century by the French physician Duchenne de Boulogne.
Evolution
Darwin published drawings of Duchenne’s work in The Expression of the Emotions in Man and Animals – his third major work on evolution.
However, the voltage was dialled down for the new experiments to ensure the safety of participants and better control the smiles.
By using computers, the team were able to control the onset of smiles with millisecond precision.
In total 47 people took part in the Essex study which was published in Social Cognitive and Affective Neuroscience.
Muscles
They were shown digital avatars and asked to assess whether they looked happy or sad. In half the trials, smiling muscles were activated at the onset of the face.
It emerged that producing a weak smile for 500 milliseconds was enough to induce the perception of happiness.
Dr Korb says the results help us understand facial feedback and he hopes to expand the study.
He said: “We are currently conducting more al research to further explore the phenomenon in healthy participants.
“In the future, however, we hope to apply this technique to explore facial emotion recognition, for people with conditions like Parkinson’s, who are known to have reduced spontaneous facial mimicry and impaired facial emotion recognition.
“Moreover, we have published guidelines to allow other researchers to safely start using electrical facial muscle stimulation.”