“Too fast!” cried Dr Susan Morris’ son as he tearfully learned to ride a bicycle. He frequently lost his balance and struggled to tell whether his bicycle was moving forward or was stationary. Later diagnosed with high-functioning autism, he continued to misinterpret visual cues in daily life, leading his mother to question whether autism and visual motion processing are intrinsically linked.
For people on the autism spectrum, the world is a bewildering place. With oversensitive sensory systems, they battle to process the maelstrom of information flowing into their brains. Often the result is sensory overload, leading to signature behaviours such as tantrums, anxiety and social withdrawal.
“Their natural ability to pare down information appears to be missing – the ‘filters’ are not working. And so whatever their behaviours are, it is to manage those filters, and keep the world constant and predictable,” Morris explains.
As a researcher in sensorimotor control, Morris has dedicated her research to exploring links between visual motion processing and autism, determined to develop interventions that reduce the disability it causes.
She has discovered that people on the autism spectrum have increased sensitivity to visual motion in their peripheral field of vision, which affects how they perceive their environment and where they place themselves in time and space.
“Most people with autism have motor coordination problems. Sensory responses influence motor responses and they feed back on each other in a loop.”
Her team’s first study determined how people used visual processing for postural control, by inducing postural illusion using muscle stimulation.
She realised that while everyone in the study leaned forward in response to the stimulation with their eyes closed, only the ‘neurotypical’ adults corrected their posture when their eyes were open.
“The people with autism did not use their vision to stabilise themselves – and that affected their motor control and movement,” she says.
The team’s second study compared the way in which people with autism processed optic flow, using streamed images of moving stars that filled their primary and peripheral vision, creating a visual illusion of self-movement.
“When the stars flow out, it feels like you are going through space and your body will naturally lean backwards. When the stars flow the opposite way, it’s like you are driving backwards through space, and you lean forwards into it.”
She observed that while everyone leaned when exposed to the whole visual field, the results were different when motion was limited to the periphery.
In the forward direction, all the adults ignored movement on the periphery – behaviour Morris believes is learned from daily activities such as driving in a car. However, in the backward direction only the adults with autism leaned forwards.
“When only part of the visual field moved, the neurotypical adults saw peripheral optic flow as something moving, whereas the adults with autism perceived it as self-motion.”
Morris likens this experience to linear vection, where an observer feels like they have moved and the stimulus has stayed stationary.
“Imagine you are on a train and then out of the window you see the train next to you start to move. For a moment you’re unsure if you’re moving or the train outside the window is moving. Perhaps this is the experience of people with autism most of the time.”
Morris is repeating the experiment with children aged between eight and 10 years to find out at which point in life people naturally learn to filter peripheral motion.
“Children have had less exposure to peripheral optic flow and so this study may determine whether visual development in individuals with autism is due to immaturity in visual information processing, or the result of a different developmental trajectory.”
While her findings could inform intervention strategies, Morris believes an individual’s brain chemistry is another consideration – specifically the activity of inhibitory neurotransmitter, gamma-aminobutyric acid (GABA).
“GABA has been demonstrated to be lower in people with autism. If GABA is not working properly, inhibitory circuits don’t work with the same timing or in the same amount as the excitatory circuits – and as a result, excitatory circuits are not switched off.”
GABA imbalance has also been linked to other brain processing disorders such as ADHD, dyslexia, central auditory processing disorder and social anxiety disorders.
“Are these conditions discrete?” Morris ventures. “People with visual disorders quite often have autistic characteristics. The fundamental underlying issue may be similar, which is related to processing information. Maybe they are all spectrums of a common problem.”
Undoubtedly, this conjecture is a topic for wider discussion, but for now Morris is developing therapies that “reduce the overwhelm” and encourage adaptation, so people with autism can lead relatively normal lives.
Now with her son fast approaching adulthood, Morris remains resolute about making a difference. When asked where her end point is, her reply is simple:
“How we see the world impacts incredibly on where we go. This project is ongoing – for the rest of my career!”
