‘Rubber Hand’ Illusion May Build Understanding of Sensory Processing In Autistic Brains

Allan Ajifo, aboutmodafinil.com, CC BY 2.0

Treating autism spectrum disorder (ASD) is difficult because the neurological anomalies that influence abnormal motor function and sensory processing are not well understood, and appear to be highly individualized. A new paper published in Proceedings of the Royal Society B by lead author Colin Palmer of Monash University describes a technique that uses an illusion to help understand how autistic brains perceive the environment.

“It is still unclear what is happening differently in the brain to produce the social, sensory and other difficulties that individuals with autism can face,” Palmer said in a press release. “We are testing a new type of theory, which implicates the brain's capacity for making predictions about its own sensory input. Autism may be related to problems with making those predictions sensitive to the wider context. This means that new sensory input is interpreted out of context, making it difficult to understand the world and to generalize to new situations.”

The technique is based on the illusion that causes an individual to perceive a prosthetic hand as their own. The subject places one hand on a table in front of him or her, and hides the other limb from view. A rubber prosthetic is put on the table in place of the hidden limb, and an outsider then strokes both hands on the table at the same time. For the test subject, the sensation of touch from the real hand and the visual stimulus of seeing the fake hand get touched cause an illusion of “feeling” the touch with the prosthetic hand.

Once the subjects “own” the prosthetic hand and perceive it as part of their own body, they are asked to reach out for an object across the table. The researchers measured the jerk-response from the subjects reaching for the object with the fake hand, which was used as a benchmark for how well the illusion worked. Those who most perceived the rubber hand as their own had a greater physical response when trying to use that hand to pick up an object. The team found that not all of the subjects responded in the same way, and there was a connection between levels of autistic features and one's susceptibility to the illusion. 

Individuals who exhibited low autistic traits were more susceptible to the illusion and had a greater response to trying to pick up the object. Those who had higher autistic traits were less likely to be influenced by the illusion. Though they could perceive the fake hand as their own during the stroking exercise, that feeling wasn’t likely to stick around and cause as much of a physical response when asked to grab an object with the fake hand.

“The study suggests that individuals may differ in how their brains draw upon contextual information when perceiving and interacting with the world,” Palmer explained. “This could contribute to sensory and movement difficulties, which are commonly experienced in autism.”

As the research progresses and more is known about how this information is processed, the findings could lead to the development of new treatment options for individuals with autism.

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