'Smile — it costs nothing' or 'A smile is the prettiest thing you can wear', if you start your day with one of these mantras, you may want to look for a new one. Though it is widely believed that smiling means we are happy, and it usually occurs when we are engaging with another person or group of people, researchers from the University of Sussex in the UK show this is not always the case.

For their study, the researchers relied on one-to-one Human-Computer-Interaction (HCI) is as if they were socially engaged. They asked 44 participants aged 18-35 to play a geography quiz game consisting of nine difficult questions so that they often got the answer wrong. Seated participants interacted with a computer alone in a room while their faces were video recorded. 

Statistically, the emotion that was most associated with smiling was 'engagement' rather than 'happiness' or 'frustration'. The frame by frame smile analysis broke down each of the nine questions into a question and answer period. Participants did not tend to smile during the period when they were trying to figure out the answers. However, they did smile right after the computer game informed them if their answer was correct or wrong, and surprisingly, participants smiled more often when they got the answer wrong.

"According to some researchers, a genuine smile reflects the inner state of cheerfulness or amusement," said Harry Witchel from Brighton and Sussex Medical School (BSMS), adding,"However, Behavioural Ecology Theory suggests that all smiles are tools used in social interactions; that theory claims that cheerfulness is neither necessary nor sufficient for smiling."

He also said that the study showed that in Human-Computer Interaction experiments, smiling is not driven by happiness but with subjective engagement. "During these computerised quizzes, smiling was radically enhanced just after answering questions incorrectly. This behaviour could be explained by self-ratings of engagement, rather than by ratings of happiness or frustration," Witchel added.