How is laughter different in people who are blind or deaf?

The groundbreaking study in this area was conducted by the human ethologist Irenaus Eibl-Eibsfeldt. He found that laughter and crying patterns are well-developed in such children. He concluded that these expressions evolved through natural selection. Deaf children have different sound patterns in their laughter, as they have in speech. Blind children seem not to display all the facial components of laughter. We're going to study these differences by statistically analysing the minute variations in laughter between different types of people. We'll video their faces while they laugh in response to various stimuli. Then we'll analyse every millisecond of their facial behaviour and vocalisation.