Revealed: The serious science behind a baby's laugh

The first attempt in 50 years to discover why infants smile can help our understanding of conditions such as autism and Down syndrome. Charlotte Philby visits Babylab HQ

With bright blue hair and tattoos, Dr Caspar Addyman is not your average scientist. But then Britain's "Babylab" is not your average laboratory. Here, inside one of the world's leading infant-research units, Dr Addyman has spent the morning filtering through the results of his new Baby Laughter project. It is the first in-depth study since the Sixties into what makes infants chuckle.

Last time around, the experiment involved a toy clown attached to a piece of string, which scientists held in front of their tiny, unwitting human guinea pigs to see if and when they would laugh. Fortunately Dr Addyman's experiment, which he launched in August this year, is a little more complex.

"Smiling and laughing are indices of our understanding of the world. Adults laugh at something when they find it surprising or unusual; it is exactly the same for babies," he explains. "Finding out what makes infants laugh teaches us more generally about how humans understand and respond to the world around them, and also the ways in which that can change."

His gleeful subjects, who are all aged between two months and two years, are helping him to hunt for information that could eventually be used to determine how different developmental groups – for instance, people with autism or Down syndrome – respond to stimuli at different stages, which might ultimately lead to interventions.

It is all smiles in Babylab HQ, at the Centre for Brain and Cognitive Development, Birkbeck, University of London. The lab was responsible earlier this year for a breakthrough study in autism which demonstrated a difference in brainwave patterns in infancy between children who later went on to develop the condition and those who did not.

In a reception room stuffed with animal wall-stickers and flashing toys, four-month-old Gaia waits with her mother, Sylvia Rigato, 30, for her turn.

"Parent-friendly" language is vital: anything that might summon up images of babies surrounded by Bunsen burners is a no-no. The studies ("not experiments") are in comfortable rooms packed with toys. Volunteers from across the country respond to adverts on baby-minded websites and magazines. Ms Rigato, also a researcher in the field, says: "It is interesting to see what babies at this age can do."

For the past two months, Dr Addyman, 38, a former banker, has been observing the humours of babies. For him, the measurement of laughter is just another tool in our understanding of how babies learn. Technologies such as eye tracking – infrared lights attached to a computer which capture corneal reflections, recording exactly what a baby is looking at – and electroencephalography, which measures brain activity, showing when and approximately where in the brain information is processed, have meant huge advances in studies in brain development over the past two decades.

But there is one thing, Dr Addyman says, that you still cannot do in a lab: make a baby laugh on demand. Accordingly he has launched his study online, allowing parents to log their children's laughter and Dr Addyman to record results as they are played out in real life. As well as being able to access participants from outside central London, it also saves the lab, which relies on grants, a fair bit of cash.

Leslie Tucker, the centre co-ordinator, explains that Dr Addyman's "crowdsourcing baby research" represents the future of information gathering: "It's a low-cost way of doing big research and getting big numbers involved." It can be more accurate, she says, because the data is compiled by parents who see their child on a daily basis, in various moods. Three hundred people have already taken part, answering questions such as "What is the most memorable example of your baby laughing?", "When was your baby's earliest smile?" or "What do you think are the main causes of your baby's laughter?"

"Although we haven't analysed the data in detail yet we can definitely see a few trends," she says. "So far, we've found that daddy seems to be the funniest person, with mummy a close second. Peekaboo is the funniest game but tickling, funny voices and blowing raspberries are all sure-fire hits."

For the record, Dr Addyman adds, we can dispel the myth that your baby's earliest smiles are just trapped wind: "A lot of first smiles and laughs are happening in the first four months of life, far earlier than traditional theories claimed. Babies' first-ever smiles are often seen as young as one to three months old, with social smiles [that's smiling at a person] starting shortly afterwards, between two and four months, and laughter following on soon, at three to six months."

Laughter and tears are our earliest forms of communication, and an insight into how the brain works at a primitive stage. "If you are trying to understand the psychology of humans," he says, "it makes sense to start with babies. Adults are far too complex. They either tell you what you want to hear or try to second-guess you." But if a baby does something, he concludes, "it's bound to be a genuine response."

Take the survey at babylaughter.net