A team led by Disa Sauter of the Max Planck Institute for Psycholinguistics in Nijmegen, the Netherlands, asked eight deaf and eight hearing individuals to vocalise nine different emotions, but without words. These included fear, relief, anger, hilarity, triumph, disgust and sadness.
Afterwards, Sauter and her colleagues played back the recordings to a panel of 25 hearing individuals, and asked them to match each utterance to an emotion.
It turned out that the only two easily identifiable emotional sounds made by the deaf participants were laughter and sighs of relief. “They seem to be the strongest,” says Sauter
The panel found it easier to guess all the other emotions if the sounds came from the hearing individuals. Even screams of terror were much less obvious from those who were deaf.
Is this conclusive? I don’t think so. But it makes you wonder.
Sauter suggests that laughter and smiling probably both evolved as important communication signals to help avoid confrontation by increasing empathy. “Even other primates laugh, if you tickle a gorilla or orang-utan,” she says.
David Ostry, who studies vocalisation in deaf people at McGill University in Montreal, Canada, says that deaf people may learn to laugh by watching how hearing people do it. Sauter agrees this is possible and has set up an experiment to investigate this.
By discovering more about when deaf people vocalise instinctively and when they need to learn, Sauter says, it may be possible to better interpret distress calls from deaf infants.