A pineapple in your sock drawer: how surprise is key to unlocking the secrets of autism

A new study has shown how those with autism are more likely to expect the unexpected.

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“Imagine opening your sock drawer and finding a pineapple instead. How surprised should you be?”

The question is deceptively difficult to answer, but it is at the heart of Dr Rebecca Lawson’s latest paper on autism in Nature Neuroscience.

Underlying the study is the fact that the brain reacts to environmental changes in ways we never normally consider. So while you may be very surprised to find a pineapple in your sock drawer in normal circumstances, you would be much less so if your seven-year-old nephew was around and causing mayhem.

Previous studies have found that those with autism are often less surprised by things that would normally surprise others, but Lawson’s study is the first to quantify this difference.

Lawson took 24 adults with autism and 25 without, and asked them to react to images on a computer screen of either a house or a face, and classify them accordingly.

During the experiment, the pictures would be preceded by tones of varying pitches which would, with varying degrees of reliability, predict what the subsequent image would be. 

The idea was to create a situation in which each image the participants were shown could be categorised as expected, unexpected or neutral. The scientists could then measure how surprised the participants were by each image, via their reaction times and the dilation of their pupils. 

Using a computational learning model, Lawson found that unlike those without autism who were very surprised by the unexpected images, the adults with autism could be more accurately described as being "mildly surprised by everything".

Overall, the results of the study showed that adults with autism had “an increased tendency to expect the unexpected” and that “adults with more severe symptoms [of autism] tended to be even less surprised”. 

As well as confirming that those with autism are less surprised by the unexpected, the study may have uncovered the neurobiological mechanism underpinning these results. Pupil size is known to be correlated with the release of noradrenaline, and more of this is believed to be secreted when one is surprised. These results suggest that an abnormal noradrenaline system may be the significant factor for why adults with autism have less stable expectations of their environment, as it is "signalling that unexpected things are happening quite readily... more so than in the neurotypical participants [without autism]". 

Lawson is currently in the process of setting up a new lab at the University of Cambridge, where she hopes to expand on her research and develop a clinical tool which may one day help doctors diagnose autism sooner. This could perhaps make the mysteries surrounding the condition a little less surprising. 

Jason Murugesu is a postgraduate student in science communication at Imperial College London, and a former Wellcome Scholar at the New Statesman.