Saccade dysmetria indicates attenuated visual exploration in autism spectrum disorder

Matt Kempen
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Dr. Nico Bast in a video abstract of his JCPP paper ‘Saccade dysmetria indicates attenuated visual exploration in autism spectrum disorder’

Authors: Nico Bast, Luke Mason, Christine M. Freitag, Tim Smith, Ana Maria Portugal, Luise Poustka, Tobias Banaschewski, Mark Johnson, The EU‐AIMS LEAP Group

First published: 25 May 2020 doi.org/10.1111/jcpp.13267

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Dr. Nico Bast
Dr. Nico Bast

Nico Bast is a post-doc researcher at the Department of Child and Adolescent Psychiatry at the Goethe University Frankfurt. He is also associated with EU-AIMS as the largest autism research project in Europe. His research applies eye-tracking in neurodevelopmental disorders. He recently gained interest in pupillometry and ocuolomotor behavior as indicators of subcortical neuromodulatory networks.

Background
Visual exploration in autism spectrum disorder (ASD) is characterized by attenuated social attention. The underlying oculomotor function during visual exploration is understudied, whereas oculomotor function during restricted viewing suggested saccade dysmetria in ASD by altered pontocerebellar motor modulation.

Transcript

Hi there.  My name’s Nico Bast and I’m a post-doc researcher at the Department of Child and Adolescent Psychiatry here at the Goethe University in Frankfurt, Germany and I’ve also been associated with the project, one of the biggest autism research projects here in Europe.  And we have recently been able to publish a study in the Journal of Child Psychology and Psychiatry, which has the title Saccade Dysmetria Indicates Attenuated Visual Exploration in People with Autism.

In the following, I want to explain the title to you by walking you through the study.  So, we have known for quite a while that people with autism look differently at seats.  So, they tend to look less on socially indicative stimuli live biological motions or higher regions of their social detection partners, so we know quite well how people with autism distribute their visual attention.  But we know surprisingly little on why this is the case.  This was the motivation for this study and we thought we should go back to basics and explore ocular motor function, which is the eye movement that defines how you are able to distribution your attention.  What did we do?  We showed our participant two types of movies, where naturalistic movie clips that either contained humans or did not show any humans at all.  We showed these videos to the sample, which are a couple of hundred of participants in the age of 6 to 30 years, that have been assessed across Europe in the last years.  While showing these video clips to our participants, we tracked their eye movement with an eye checker and the eye checker is able to assess three main features of ocular motor function, fixations, saccades and pupil dilation.  So the fixation is when your eye is at rest and is the main source of visual information intake.  A saccade is a fast movement of the eye ball, which reorients your visual attention, and pupil dilation, apart from luminants adaption, also indicates cognitive processes, like cognitive load.

So, we explored in linear mixed model whether there are differences on these ocular motor features in people with autism, compared to neuro typical controls.  What did we find?  Interestingly, we did not find any differences in fixation or pupil dilation features and we are convinced that this is a true null finding, because we had sufficient power with around 300 videos in our study.  But what we did find was a different saccade behaviour.  People with autism tend to show shorter saccades and saccades that have a smaller amplitude.  More importantly, this was independent of the video content, so no matter if there were humans or no humans, in the movie clips, the people with autism had these different saccades, and it indicates that it cannot be explained by attenuated social attention.  We are convinced that our findings may suggest that people with autism show a different visual exploration of scenes.  When your saccades are shorter and don’t go that far, your fixations will stay spatially cluttered, so people with autism tend to be less able to explore a scene and this is independent, as I said, if they’re humans or no humans in it.

This different functioning of saccades is controlled by a subcortical network, the pontal cerebellar ocular motor network and this network has been neglected in previous imaging research, because it’s so deep in the brain and difficult to track.  So we may suggest that we should maybe focus on this subcortical network in the future and we think that our findings of attenuated visual exploration may explain a lot of cognitive findings that we have in autism.  For example, an increased focus on local features in attenuated perception of global features and the delayed reorienting of attention.  So, this might all be due to a different saccade behaviour, this saccade dysmetria.

We know that our findings are limited.  We excluded individuals that were below clinical cut offs, so our findings are not representative of the broader autism heterogeneity and we did not explicitly relay ocular motor function to social attention.  So, our findings need replications in independent samples, but we ought at first to show that the visual exploration of people with autism is different and this difference is due to a different saccade behaviour.

So, if you have any questions on this study, feel free to send me a message and thank you all for listening.

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