(Part V in a series of posts that will eventually take us to a highly contagious and dangerously inaccurate meme about what autism is.)
My previous post drew a connection between the severity of autism (whose diagnostic measures include Joint Attention behaviors) and the severity of the language impairment associated with autism. This connection, I suggested, explains why a significant proportion of people on the spectrum (somewhere around 25%) are nonverbal.
But does this mean that everyone who is nonverbal is so because of Joint Attention deficits? Are there other reasons why someone on the autism spectrum might be, or appear to be, nonverbal?
The answer to this question depends in part on what we mean by “nonverbal.” Do we mean unable to produce any language at all, or unable to speak?
As far as not being able to speak goes, there are other culprits besides Receptive Joint Attention. Profound hearing loss is one. If you can’t hear other people’s speech or your own oral output, then, absent intense speech and language therapy, you’ll likely remain orally nonverbal. Apraxia of speech is another. From the NIH:
AOS is a neurological disorder that affects the brain pathways involved in planning the sequence of movements involved in producing speech. The brain knows what it wants to say, but cannot properly plan and sequence the required speech sound movements.
I highlight this definition of Apraxia of Speech not just because the condition is less familiar than deafness, but because it has been found to be co-morbid with autism. This means that a significant number of nonverbal individuals have both autism and AOS.
Putting all this together, we see that in some cases the primary culprit for lack of spoken language may be apraxia of speech rather than autism-related Joint Attention deficits. If so, then the autism itself may be relatively mild. In particular, the person’s receptive Joint Attention behaviors, along with his/her ability to pay attention to what people are doing when they speak, may be only mildly impaired. In this case, he or she should be able to acquire receptive language–to learn to understand what people say–even if he or can’t speak.
But the inability to speak doesn’t entail the inability to produce other forms of language–for example, written language or sign language. For more on the broader sense of verbal/nonverbal, stay tuned.