We intuitively understand the meaning behind a touch to the arm

It's common knowledge that we use more than speech to communicate. Our facial signals, hand gestures and tone of voice can communicate everything from anger or surprise to love and joy. And now a new study in Psychological Science reveals something perhaps even more remarkable: humans also have an intuitive — and quantifiable — language of 'social touch'.

For an initial study, Sarah McIntyre at Linköping University in Sweden and colleagues recruited 16 pairs of adults who were emotionally close and comfortable with touching each other (these were not only people in romantic relationships, but also close friends). Each member of the pair took turns at being the 'sender' and the 'receiver' of messages that had to be transmitted by touch alone.

The receiver sat in a chair, with their back to their partner, with a curtain between them. Only the receiver's bare arm was accessible to the sender. In each trial, the sender was told which of six messages they should endeavour to convey: love, happiness, sadness, gratitude, a calming message, or a bid for attention. Without making any kind of sound, they had to use one hand, and whatever type of touch they wanted. The receiver then had to indicate which of the six messages the sender had in mind.

Overall, the receivers did a good job — well above chance — of guessing/understanding the messages, and this was true for each of the six types of message. This was despite the fact that neither partner had received any training in the use of touch for conveying messages. "This demonstrates that social touch messages are readily communicated within emotionally close pairs," the researchers write.

The team had videoed all these interactions. They analysed these videos, and identified the key features that were associated with the most successful communication of each of the six messages. Here's what they found:

Attention: moderate tapping and shaking

Calming: light holding at multiple locations on the arm as well as moderately stroking the whole arm or lightly stroking part of the arm

Gratitude: light stroking or holding, or squeezing the arm

Happiness: light tapping across the entire arm

Sadness: lightly holding or stroking one part of the arm

Love: light stroking across the whole arm

They also noted that if the sender touched the hand, rather than the arm, and used high intensity movements, they were generally unsuccessful at communicating the message.

The researchers used this information to generate standardised touch gestures for each of the messages, and trained three experimenters in how to use them. A fresh batch of participants then came into the lab, and the initial study was repeated. This time, though, the receivers got messages not from someone they knew well but from a stranger – one of the experimenters - who was using the standardised touch messages.

The results showed that, as in the first study, the correct response was generally the one that receivers chose most often (only for gratitude was this not the case). But also, these receivers were actually better at recognising love and happiness and a calming intent than the receivers in the first study.

The reason, the team suggests, is that their video analysis allowed them to come up with the clearest, most readily understood, touch gesture for each message. "Thus, the possibility emerges of a standardized, intuitively understood language of social touch," they write.

The findings could clearly have implications in the real world. Haptic devices could be programmed to use these touch gestures. And people who find it hard to communicate verbally might be trained to use these gestures to better convey their emotions.

It is worth stressing that this study was conducted in Sweden; more work in other cultures will be needed to explore if there really is a standard, universal language of touch. But these initial findings are certainly compelling. Of course, before we can speak or understand words, we receive messages from a caregiver via touch. As adults, many of us also experience regular touch with loved ones. So it makes sense to think that we should be able to understand, and learn how to convey, certain signals in this way.