Neuroscientists reveal autism's 'noisy' secret

May 26, 2015
autism
Quinn, an autistic boy, and the line of toys he made before falling asleep. Repeatedly stacking or lining up objects is a behavior commonly associated with autism. Credit: Wikipedia.

Strapped into a motion-enabled simulator and wearing 3D glasses, 36 adolescent volunteers recently experienced what it was like to "travel" through a field of virtual stars. The experiments provided new and convention-busting data about how sensory stimuli are processed by the brains of individuals with Autism Spectrum Disorder.

The study, entitled "Self-motion perception in autism is compromised by visual noise but integrated optimally across multiple senses," was published online in the Proceedings of the National Academy of Sciences on May 4th, 2015. The authors of the study are Adam Zaidel, of Israel's Bar-Ilan University, and Robin P. Goin-Kochel and Dora E. Angelaki, of Baylor College of Medicine in the United States.

Perceptual Impairment in Autism - a "Noisy" Controversy

One of the hallmarks of Autism Spectrum Disorder (ASD) is superior low-level task performance alongside reduced performance in tasks that involve the processing of complex sensory data. This has led to the assumption that autism is characterized by a difficulty integrating individual units of perceptual data into global concepts. In line with this first assumption, it has further been proposed that individuals with autism have difficulty integrating multi-sensory input.

With its unique experimental set-up, the new study has successfully challenged this conventional wisdom. Moreover, it has identified a neurological phenomenon associated with autism pathology: a heightened sensitivity to "noisy" sensory signals.

"Theories of global and multisensory integration deficits in ASD are deeply rooted in the scientific conversation about autism," says Dr. Adam Zaidel, a member of Bar-Ilan University's Gonda (Goldschmied) Multidisciplinary Brain Research Center, who is the publication's lead author. "Recently, this notion has come under scrutiny, as more and more investigators have observed discrepancies with experimental results."

"In this study we show that heightened sensitivity to sensory noise - the random signals inserted into the visual tasks traditionally used by scientists to test sensory integration levels in autism - may provide an alternative explanation for impaired performance. When this noise is removed from the equation, the integration of visual motion stimuli in ASD is equal to, or maybe even superior to that of the . Moreover, our study demonstrates that the multi-sensory integration seen in autistic participants was comparable to that of the non-autistic control group."

A Problematic "Twist" in Traditional Testing: Noise

Zaidel explains that visual motion processing in ASD has generally been examined through the use of a computer-based tool in which study participants are asked to designate the overall direction of motion of a field of dots, while a certain number of dots - the "noise" in an otherwise coherent picture - are randomly displaced. In these experiments, the level of noise at which participants can no longer determine overall direction is seen as a measure of the participant's innate ability to integrate isolated visual stimuli into a global picture.

Zaidel's new approach proves that such traditional methods - which depend on noise as a modulator of task difficulty - have led to widespread misinterpretation of how individuals with ASD integrate visual stimuli.

"Our study is carried out in a 3D environment in which a field of moving dots generates the feeling of traveling through space, with different trials 'steering' to the right or left of straight ahead," Zaidel says. "By asking participants to indicate their perceived direction of movement, we test their ability to create a global picture out of individual details. Significantly - and this is where our method differs from previous tests - we can achieve measureable results both when randomized dots are included in the overall picture, and in a completely coherent, noise-free environment."

Zaidel says that when there were no randomly-moving dots, autistic participants performed well, successfully determining the direction of movement at a level similar to that achieved by the non-ASD control group. When the noisy signals were introduced, however, the ASD group was significantly more affected than controls. This indicates that it is the presence of noise - rather than any innate integration deficit - that makes the task more difficult for people with autism.

No Deficit: Re-Thinking Multi-Sensory Integration in ASD

The unique experimental platform also allowed Zaidel to challenge another theory that has emerged more recently: that people with ASD are neurologically pre-disposed toward deficient integration of multi-.

The simulator used in the study was equipped with an ability to introduce movement into the chair in which the study participant was sitting - requiring the participant to respond to and interpret visual and vestibular stimuli at the same time.

"By adding movement to the experiment, we created a situation in which participants didn't just see the direction of the movement, but felt it as well," he says. "In this scenario, people with autism displayed intact multi-sensory integration, completing tasks in a normative manner, both in a coherent, noiseless environment, and even when noise was present. These findings raise questions about prevalent theories related to multi-sensory integration deficits in ASD."

Autism Thinks: Processing Sensory Stimuli vs. Accessing Prior Knowlege

According to Zaidel, the new study provides support for the idea that people with autism are highly sensitive to incoming sensory information. Moreover, he suggests, they are predisposed toward relying more highly on external stimulation - with less use of prior knowledge - when interpreting the world around them.

"Our results suggest that people with autism may experience a deficiency in what are known in the scientific literature as Bayesian priors - the ability to draw on existing knowledge to understand what we see and to predict what we will see in the near future," Zaidel says. "If you're more heavily weighted toward perceiving the world bottom up - from stimulus to perception - and relying less on rules of thumb from prior knowledge, perception will be both more taxing, and more sensitive to sensory noise."

In the future, Zaidel says, it may someday be possible to study this phenomenon directly in the brain, or to create treatments that might help autistic individuals become more adept at re-connecting to and using prior knowledge. However, he adds, future advances will depend on getting a clearer picture how the autistic brain processes and priors.

"In recent years, predominant theories about the nature of autism have become the subject of debate in the scientific community," he says. "At the same time, the incidence of ASD diagnosis is on the rise. It is vitally important to understand autism's underlying neuropathology, so that scientists can create the studies that have the best chance of helping us face this challenge."

Explore further: Brainwave test could improve autism diagnosis and classification

More information: Self-motion perception in autism is compromised by visual noise but integrated optimally across multiple senses, Adam Zaidel,  6461–6466, DOI: 10.1073/pnas.1506582112

Related Stories

Discovering age-specific brain changes in autism

March 26, 2015

The field of autism research has tried to find a central theory underlying brain changes associated with autism spectrum disorder (ASD). Now, a new study shows that individuals with the disorder exhibit different patterns ...

Recommended for you

Study tests the 'three-hit' theory of autism

March 7, 2017

Since the first case was documented in the United States in 1938, the causes of autism have remained elusive. Hundreds of genes, as well as environmental exposures, have been implicated in these brain disorders. Sex also ...

3 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

tadchem
not rated yet May 26, 2015
I just love it when 'conventional wisdom' gets challenged.
tinytim
1 / 5 (3) May 26, 2015
Here's what informed parents know:

Neither the doctor nor the vaccine maker has any liability for vaccine damage they've been protected by federal law. Instead victims have to appeal to a federal program where they're up against government lawyers defending the government's vaccine schedule, using government money. Few people ever receive compensation. Those that have report it took between seven and fourteen years.

The current vaccine schedule has more than tripled since 1983 without a single study on the cumulative effect.

Officials refuse to call for the one study that could settle the debate over vaccine safety immediately. There has never been a simple study comparing the health outcomes of fully-vaccinated and never-vaccinated children. If never-vaccinated kids also have the same health problems that vaccinated ones have-namely, autism, learning problems, asthma, diabetes, severe allergies, seizure disorder, sleep disorders the proof of no would be there for all to see.
Nik_2213
3.7 / 5 (3) May 26, 2015
" If never-vaccinated kids also have the same health problems..."

They do. Just venture beyond the anti-vaxxers' sites...

Actually, they get really, really sick and get all sorts of problems from a dozen different, life-changing nasties they could be vaccinated against, that our parents worked so hard to beat.

And, if they get measles, it wipes their previous acquired immunities so they can get sick all over again. I'd call that 'Double Jeopardy'...

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.