Ever wonder why an autistic person who has no spoken language can’t just learn to sign the way deaf people do?
The reason behind this is nothing short of fascinating.
It seems like a no-brainer: If an autistic child can’t speak, have them learn American Sign Language (ASL) – along with other family members so that everyone can communicate, the way people do when they learn their child is deaf.
Since my diagnosis of autism, I’ve met a lot of nonspeaking (complete lack of speech) autistic adults and a few teens at autism resource fairs, events for developmentally disabled adults, and as a direct support professional for a few agencies.
Not one of these never-talking individuals could execute ASL – not even at a rudimentary level that we might see with a deaf preschooler.
Of course, most of these autistic adults have learned to use basic signals and gestures that would seem to come intuitively to anyone who can’t talk.
For example, they might hit their palm several times on a table to indicate “Put my drawing right here.”
A nonverbal woman I work with curls her index finger to her thumb to signal she needs to use a restroom.
The Role of Intelligence
Sign languages are full languages on their own, with complex grammar and meaning, says research from the Max Planck Institute for Human Cognitive and Brain Sciences.
Deaf individuals don’t just use American Sign Language to express basic needs; they communicate in complex ways to narrate their daily life experiences, describe their feelings, conduct business meetings and express anything else that hearing people normally do.
Why can’t nonverbal, never-speaking people with autism do this as well?
It’s easy to simply attribute this to a low IQ that happens to co-occur with the autism.
It’s tempting to believe that when severe intellectual impairment is superimposed on a brain with autism, the result is absent speech – even though non-autistic or neurotypical people with severe intellectual disability might be talking in full sentences.
Might the severe intellectual deficit also be what prevents learning ASL?
Though intellectual disability frequently occurs alongside autism (one does not cause the other), the lower IQ is not the reason that speech or the ability to learn ASL is absent.
So why can’t they still learn American Sign Language?
That’s because the area of the brain that enables speech via mouth is the same area that enables “speech” through the hands.
The intention to talk, even a single word, begins in a region of the brain called Broca’s area.
If this area is normal, that intention gets converted to neuron signals that culminate in the physical output of that intention: full speech.
This same motor planning process occurs when the intention is to “talk” by using one’s arms, hands and fingers in ASL.
So if there’s a disruption in the expressive language motor planning that originates from Broca’s area, both speech and systematized sign language will be impaired.
Speech, ASL and Broca’s Area
Researchers at the Max Planck Institute for Human Cognitive and Brain Sciences wanted to know which brain regions are involved in processing sign language and how much these areas overlap with the regions used for spoken language.
They conducted a meta-study, combining data from sign language experiments around the world.
The study showed that Broca’s area was active in almost every sign language study they looked at.
How this Fascinating Study Was Done
The team compared the results of those sign language experiments with a huge database of brain scans from thousands of studies.
They confirmed that Broca’s area is used for both spoken and signed language.
This is, precisely, why never-speaking people with autism just can’t learn ASL.
Intention to speak → motor planning sequence → physical output (speech, signing, writing, typing)
Broca’s Area As a Central Language Hub
The findings show that Broca’s area is the headquarters in the brain’s language network.
It works together with other networks depending on whether language comes in the form of signs, speech or writing.
Broca’s region handles abstract linguistic information in general, not just spoken language.
This makes it more understandable why an autistic person with impaired speech execution would also struggle with learning American Sign Language.
