Diagnosing someone with autism spectrum disorder (ASD) requires a whole host of different inputs, and various involved evaluations. But there may be one simple test that could help, and all it involves is looking at an optical illusion.
A new study published in the journal eLife has found that the changes in the size of a patient's pupils as they watch the optical illusion of a three-dimensional cylinder spinning correlates with the likelihood of having autistic traits. This is not, clearly, solid evidence that someone is autistic, and would never be used solely for a diagnosis, but it could feed into evaluations, and help identify people who may have ASD.
It works by taking advantage of how the pupils change size depending on whether a person is looking at light or dark images. This, in turn, can be used to track someone's attention, by giving a rough idea of what part of a screen they are focusing on.
It is this phenomenon that forms the basis of the optical illusion used in the study. It consists of a gif, in which there is a sheet of white dots moving in one direction, and a sheet of black dots moving in the other. For most people, this gives the illusion of a three-dimensional rotating cylinder.
But how you see the cylinder differs from person to person. Some need to focus on the dots that would form the front of the cylinder to see it, with focusing on the white dots causing it to rotate left and focusing on the black dots making it rotate right. But others can view the image in three dimensions by looking at it as a whole, focusing on all the dots at the same time.
How an individual looks at the illusion affects what their pupils are doing. Those who are more detail-focused tend to look at only one color of dots at a time and flick between them, which makes their pupils oscillate in size. Those who look at the image as a whole, however, have pupils that remain constant.
Before being shown the image, participants in the study were asked to complete a questionnaire. Those who scored higher on it were more likely to have autistic traits than those who scored lower. Following the questions, they were then asked to look at the image, and their pupil responses were measured.
Fascinatingly, the researchers found that those whose pupils oscillated when they watched the optical illusion also tended to score higher on the questionnaire. They think that this is possibly to do with the fact that autistic people, or those with autistic traits, are simply more detail-focused, and so pay more attention to the individual sets of dots rather than the image as a whole.