Smile like you mean it

The Duchenne smile has widely been believed to be a key indicator that the person smiling is genuinely experiencing a positive state. This smile includes the movement of upper facial muscles, such as the orbicularis oculi, pars lateralis, which cause the crinkles round the eyes seen in a genuine smile (also known as crows feet) seen here. The general understanding being that, while people can consciously move the mouth muscles (zygomaticus major) to form a smile, the upper muscles are not so much under conscious control and are more likely to betray a person's 'true' feelings.

However, a recent paper highlighted by Psyblogs indicates that the Duchenne may not be the silver bullet for identifying a person's felt state. The paper indicates that, contrary to long held expectations, the vast majority of people can create the Duchenne smile on demand. Moreover, photographs of this smile can fool other into thinking it is a genuine expression.

A further experiment in the paper indicates that people can determine if a smile is "Duchenne" even when the top half of a face is masked, and the marker of Duchenne-ness is not present. This indicates that there are other indicators that we use to identify between smile types. The final study indicates that the dynamic process of a smile may also be relevant to someone working out if it is genuine. Indicators of a non-genuine smile include asymmetry and a shorter peak intensity alongside more obvious, non-positive affect indicators such as frowning or lip pressing.

The Duchenne smile then does not seem to be this foolproof indicator that a person's smile is genuine. Even some of the spontaneous smiles (and presumably genuine) shown by participants lacked the key orbicularis oculi, pars lateralis movements.

One consideration not mentioned in the paper though is just how people who were required to fake smiles approached the task. In the occupational psychology literature, there is a distinction made between surface acting and deep acting. The former is to just fake an expression and the latter is the changing of one's own emotional state, which then may feed-forward to naturally affect expressions. If participants engaged in deep acting because they wanted to present convincing smiles, this may trigger spontaneous smiling.

Even if this is the case though, the smiles still didn't get past observers when they're watching the smile on video. Perhaps deep-acting is too slow of a process to manage felt and expressed states to give that all important genuine expression.

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