Excerpt from a Physiology News feature by Sophie Scott, Institute of Cognitive Neuroscience, UCL, London, UK, @sophiescott
Human vocal communication is primarily studied in the form of human speech – a remarkable talent and evolutionarily highly specialised motor act that involves high levels of precise motor control over the articulators and over breathing. However, we do not solely communicate vocally with speech: when we are in the grips of more extreme emotion, we frequently start to produce non-verbal vocalisations, often in a relatively involuntary fashion. This includes vocal behaviours such as screaming, sobbing and laughing.
The physiology of laughter
I ﬁrst started working with these kinds of vocal acts in the 1990s, when I was collaborating with colleagues who were studying neuropsychological patients who had speciﬁc deﬁcits in the perception of emotions. […] The characteristic ‘ha ha ha’ sound is driven by the involvement of the intercostal muscles: normally used smoothly to pull air into and out of the lungs during metabolic breathing, and to produce a constant sub glottal pressure, to vibrate the vocal folds during speech and song, the intercostal muscles and diaphragm start to produce large contractions during laughter, each of which contributes to a single ‘ha’ burst, as air is forcibly exhaled (NB it is also possible for these contractions to be largely acoustically silent).
Laughter is more like a different way of breathing than it is a different way of speaking.
If these contractions start to run into one another, then the laughter can start to sound more like silent wheezing. From this perspective, laughter is more like a different way of breathing than it is a different way of speaking. Another physiological change is a constricting of the pharynx, meaning that some sounds are made during laughter as a consequence of this constriction (e.g. glottal whistles). The intercostal contractions made during laughter are much greater than those used to control breathing during speech production, and this also affects the noises made during laughter, with very high pitched noises being produced, which would be difﬁcult or unlikely to produce under voluntary control. My laugh can be very high pitched, and I can hit pitches when laughing that I would be unable to produce while singing.
Rats don’t laugh at jokes, and neither do we
Laughter is an interesting human behaviour to study, even in isolation: it appears to be a universal emotional expression, however claims that only humans laugh have transpired to be incorrect. Laughter has been reported in gorillas, chimpanzees and orangutans, where it can look and sound quite similar to human laughter. However, we are unable to hear many of the noises made by other animals, meaning that there may be many more examples out there: it’s also probably true that no one is out there looking for laughter. Certainly a vocal behaviour which is contextually identical to laughter has been described in rats: rats make a distinctive chirping sound when they are playing together, and when they are being tickled, and when they are anticipating being tickled. Indeed, at its heart, Panksepp has argued, laughter can be considered an invitation to play.
We are 30 times more likely to laugh with someone else than if we are on our own.
As all mammals play when juveniles, and some continue to play through into adulthood (dogs, humans, otters), this argument would suggest that laughter is likely to be widely found across mammals. This role in play seems counterintuitive to humans adults, who strongly associate laughter with humour, jokes and comedy, however Robert Provine has shown that even in humans, laughter is primarily a social behaviour, which is strongly primed by other people – we are 30 times more likely to laugh with someone else than if we are on our own.
We are laughing to show that we like people, understand them, agree with them.
What this means in practice is that we are laughing mostly when we are in the company of others – and we are still not laughing at jokes. Indeed we laugh mostly at comments and statements and although we report laughing because we are amused, we are laughing to show that we like people, understand them, agree with them, are afﬁliated to them as much as if not more than because something is ‘funny’. Within conversations, laughter is very tightly co-ordinated, with members of a conversation laughing together at the end of sentences, even if the conversation is in sign language rather than a vocal language, and in theory people could be laughing all the way through if they wished to. We also laugh much more often than we report: all studies that have compared actual to reported laughter ﬁnd that people laugh more than they say they do. Indeed, laughter is probably the most commonly encountered non-verbal vocal emotional expression, occurring at around 7 times per 10 minutes of conversation. Provine has also noted that laughter is highly behaviourally contagious, and people will frequently laugh simply because others are laughing. Like other such contagious behaviours, such as yawning, contagious laughter is modiﬁed by social factors, and people are much more likely to catch a laugh (or a yawn) from someone they know than from a stranger.
Read the full article in Physiology News.
Watch Sophie’s TED talk, Why we laugh.