Optical illusion: People with autism are more likely to be taken in by certain magic tricks.

Magic is all about managing expectations. A good magician knows when and where the audience will be looking and — poof! — does the mechanics of the trickery elsewhere.

Despite the impressive stories of people with autism being able to spot fine details, however, they are surprisingly susceptible to a magic trick called the ‘vanishing ball illusion,’ according to a study published in October in Psychological Science.

The trick goes like this: a magician throws a ball into the air and catches it a few times. Then, on the final toss, he surreptitiously keeps the ball in the palm of his hand, making it seem like it vanished into thin air. (You can watch the study’s lead investigator, Gustav Kuhn, demonstrate the ruse.)

It’s a cheap trick, but still manages to fool about 70 percent of people watching it. In 2006, Kuhn’s team showed that the illusion is ruined if, after the imaginary ball toss, the magician looks at his hand, rather than up in the air. This is consistent with eye-tracking data showing that participants spend a lot of time looking at the magician’s face.

You’d expect that individuals with autism — who pay close attention to visual details, but have trouble reading facial expressions — would not be easily fooled by any of the hocus pocus. Kuhn’s study found exactly the opposite.

The researchers recorded the eye movements of 15 high-functioning adults with autism as they watched a clip of the vanishing ball illusion and asked them to figure out how it was done. Compared with healthy controls, those with autism are less likely to understand the trick, the researchers found.

Although all participants looked immediately at the magician’s face and eyes, those with autism did so 267 milliseconds later than controls did. They were also less likely to look at the ball when it was in the air.

The research adds to the growing number of studies linking the disorder to problems with attention and the perception of time.

But more interesting, I think, is that the researchers claim these findings challenge two widely held notions: that people with autism avoid looking at faces, and that they have super-keen visual acuity.

It’s a provocative idea, but this interpretation of the data involves a bit too much hand waving for me. The researchers only tested high-functioning adults who, perhaps, learn to pay attention to social cues over time. They plan to repeat the experiments on children with autism, which should be far more illuminating.