Social functions of smiles and laughter
We can think of nonverbal expressions as tools people use to elicit specific behaviors from others. A cry of pain elicits caregiving behavior, while a wide-eyed facial expression of fear cues other people to detect and avoid the threat. Our social functional framework for studying nonverbal expressions categorizes expressions by their social consequences rather than by the internal feeling state of the expresser. Much research on smiles and laughter describes them according to whether they are readouts of genuine positive emotions (like joy and amusement) or volitional attempts at portraying positive emotions ("fake" happiness). Applying a social functional framework explains the full complexity of smiles and laughter that we all see in the real world, which often does not fit the genuine-fake dichotomy. We suggest that all three social tasks can be accomplished with varying degrees of intentionality or automaticity.
Below are descriptions of three tasks, which we see as fundamental to social living, that smiles and laughter can accomplish. Dr. Niedenthal and colleagues introduced these ideas in 2010, which we will further explore in an upcoming Trends in Cognitive Sciences review. Although we assume high variability in the physical form of smiles and laughs that accomplish each of the 3 tasks, we have used perceiver-based techniques to develop prototypical examples of smiles (2017) and laughter (2017) that perceivers understand as serving the social tasks (smile examples are below).
Some smiles and laughter feel good to produce and perceive, and can therefore act as social reinforcers, or rewards. We think nonverbal reward signals are especially important tools for pre-verbal infants, who use the smiles and laughter of their caregivers to shape their own behavior. By producing reward smiles and laughter, babies are also able to reinforce and maintain caregivers' attention, which is crucial for their survival. Smiles and laughter that serves a rewarding function are probably most common within established relationships. Reward expressions include what previous researchers refer to as "spontaneous" or "genuine" smiles and laughter, and therefore have similar physical properties.
Smiles and laughter that primarily serve an affiliation function may be the most ubiquitous in everyday life. Affiliation expressions signal non-threatening, friendly intentions, and smooth over interactions. Watch for these smiles (such as the one to the right) when you pass strangers on the street or in the elevator. They acknowledge the presence of another person and convey benign intentions without necessarily being rewarding. Affiliative laughter includes the chuckles and giggles that occur frequently during conversation and sound friendly but not "genuinely amused."
If you try to imagine how a villain in a movie might smile and laugh, you will realize that these expressions do not always make you as a perceiver feel good or safe. We propose that some smiles and laughter serve the dominance function of elevating the social status of the expresser and conveying superiority. At the most basic level, smiles and laughter convey harmlessness. Expressers can embed their aggressive intentions in one of these "harmless" signals, thereby negotiating dominance without disrupting the interaction with outright aggression. Such expressions may be directed towards outgroup members, such as fans of a rival football team, but they may also be directed towards ingroup members who transgress group norms in some way. You can imagine a deep, barking laugh of derision one friend makes when another friend says something stupid. That laugh conveys momentary derision without necessarily harming the relationship.