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Sensory Processing is Only Half the Story: Movement Differences in Autistic People

For more in-depth information on this topic, I recommend this book. Other research can be found here.

I wrote this article a few months ago and am reviving it on the heels of a new systematic review in this area: “Early Motor Function of Children with Autism Spectrum Disorder: A Systematic Review” (Pediatrics, February 2021).

Sensory differences are broadly recognized by autistic self-advocates with fluent speech (those of us who may have traditionally been labelled as “Asperger’s” or “high-functioning”), but I see less discussion about movement differences in neurodivergent people.

There are reasons for this, of course. It’s partly about who controls the narrative. We continue to see autistic people described or shown as behaviourally challenged, even though there is evidence that differences in motor functioning may be a core component of “autism spectrum disorder,” alongside sensory differences. (This study is one example. Even Spectrum News has reported on this topic.)

Another reason is that, when a person doesn’t have a baseline to compare against, they have trouble identifying exactly how their experiences may be different from others. This is probably familiar to anyone who was diagnosed with a neurodivergent condition later in life. Many of us have been told that our symptoms are intentional misbehaviour, perhaps being called “lazy” or “attention-seeking.” It wasn’t explained to us that some of our behaviours are characteristic of neurological differences affecting movement.

I think, though, that understanding “autism” as a sensory-movement disability, rather than as a social disability, might help autistic people to not only better understand ourselves, but to better understand other autistic people. This makes us better equipped to provide advice to parents and professionals.

“Sensing = input” / “Moving = output”

If you aren’t familiar with the structure of the brain, you should first know that sensing and moving are anatomically related. There are 12 pairs of cranial nerves in your brain, which attach to other parts of the body. These nerves have two responsibilities: (1) they transmit stimuli from your environment — what your body sees, hears, smells, tastes, touches — to your brain to interpret, and (2) they transmit impulses from your brain to your body. 

The brain cells (neurons) involved are either “afferent” (moving inward, towards the central nervous system) and “efferent” (moving outward, away from the central nervous system). Put plainly, what our bodies sense is the input that our brain receives, and how our bodies move is the output that our brain provides. 

In my experience, what all autistic people have in common, when compared to the neurotypical population, are major differences in (1) how our brains interpret signals that we sense with our bodies and (2) how our nervous systems react to those signals.

We could also refer to these two areas as “sensory processing” and “motor functioning,” respectively.

Here’s a diagram of the cranial nerves from Medical News Today.

The text on the image identifies the 12 cranial nerves:

The Importance of Collaborating with Autistic People

I’d like to explain why the concept of autism as a sensory-motor disability appeals to me:

First, the more that I read about sensory-movement differences, the more of my own lived experience as an autistic person start to make sense. As self-advocates, we often say that “autism” isn’t a thing that we have, but a way of experiencing the world. Now I understand exactly what about me is causing me to have a different experience.

Second, researchers who proposed the theory have a long history of working collaboratively with autistic people and encouraging others to do the same.

It should be obvious – to anyone – that, in order to understand what “autism” actually means and how to best accommodate autistic people in general, you must include the stories of autistic people with all different experiences. This is one of the areas where autism research, especially in the area of behavioural psychology, tends to lag behind. 

We are seeing advances in understanding autistic people in other fields of research that behavioural therapists are either simply not exposed to, or refuse to acknowledge, claiming lack of evidence.

Of course, the frustrating part is that these behavioural therapists are often the first line of contact for parents of autistic people, and unless they do outside research, parents never receive this information either.

Similarly, self-advocates who don’t make efforts to collaborate with other self-advocates, including and especially nonspeaking autistic people, risk being biased in their interpretations of what it means to be autistic.

Within the self-advocacy movement, we are faced with the enormous task of both convincing parents and professionals that they’ve got it wrong and succinctly explaining why they’ve got it wrong. I hope to help contribute to the “why.”

Symptoms of Movement Differences in Autistic People

This article is inspired by reading the first chapter of “Autism: Sensory-Movement Differences and Diversity,” written by Anne Donnellan and Martha Leary. (The book is free to read if you happen to have Kindle Unlimited.) 

The chapter compares and contrasts sensory and movement differences that are recognized as being neurologically-based when seen in non-autistic people, but are labelled as intentional “behaviours” when seen in autistic people.

I think some people don’t entirely understand what it means to say someone has a motor-based disability; they’ll suggest that if someone can do this, they clearly have perfectly working motor function, and they should also be able to do that

For example, if a nonspeaking autistic person can walk, reach for food, or pick something up, someone may claim that their inability to speak, then, cannot be related to motor functioning. 

I believe this generalization of ability is unwarranted, particularly when it is common knowledge that the abilities of autistic people vary from person to person. It’s particularly unwarranted with speech, which is much more cognitively complex and less automatic than other movements.

Donnellan and Leary’s work includes the following table, which I’d like to reproduce, as I think the information is valuable. (If the concepts feel too dense, feel free to skip to the next section where I discuss some differences in plain language.)

The left side of the table lists a number of characteristics that are commonly recognized as being “movement disturbances” that are neurological. The right side lists examples of “autistic” behaviours (“documented and observed throughout many years of clinical practice with a large number of individuals with autism across the life span.”)

Movement disturbance featureSymptoms evidence in autism
Repetitive motor actionse.g., Tapping, touching, grimacing
Rhythmical, cyclical movements e.g., Rocking, shrugging, squinting, pouting
Lack of initiationRequires prompts and cues to perform
Difficulty imitating others’ actionsBoth immediate and delayed motor imitation difficulties
EchophenomenaMimesis; elaborate copying of others’ actions – verbal and/or motor
ImmobilityRemains fixed and inert in position and posture for extended time periods
WithdrawalIsolates self away from focal activity and others
GrimacingFacial/oral-motor movements
StereotypiesRepetitive movement of the hands, limbs, extremities, and whole body
AversionOf eye gaze and attention to others
NegativismOppositional actions elicited with passive movement and overall behaviour
Automatic obedience; suggestibilityExtreme compliance in response to verbal suggestion and environmental cues
RigidityMuscles rigid to passive movement
BradykinesiaSlowness of movements, feebleness
TremorEssential, intentional, rest, postural, etc.
Forced graspingOf another’s hands, wrists, etc., or items in the environment
AkinesiaMarked absence of action and movements
Akathisia Motor restlessness, moves about but not goal-oriented
AtaxiaLoss of coordination in motor action execution
PerseverationMotor or other repeated behaviour after being elicited an initial stimulus
AmbitendencyAppears “stuck” in indecisive, hesitant movements
TicsMotor and/or verbal
Obstruction; blockingIncomplete movement towards a goal – “gets stuck” en route to goal
Difficulty with stopping, cessation of movementWill continue movements unless redirected or stopped by external means
MannerismsUses intact and entire motor action sequences out of context; e.g., salutes
Wavy flexibilityAutomatic ease and compliance with assuming unusual postures for extended time
BallismusViolent, rapid, and apparently involuntary actions and movements
Choreiform movementsRapid and apparently involuntary traveling and “dancing” ripples of movement
Catalepsy (posturing)Maintains seemingly uncomfortable and imposed postures for extended time
Atheloid movementsSlow, writhing movements and actions
SpasmsMuscular spasms of varying durations affecting muscle groups
DystoniasSustained torsion due to muscle contractions in varied muscle groups
ImpulsivityActions and movements triggered suddenly
Self-injury, mutilationDisturbing and persistent attempts to inflict pain on self
Excitement; frenzyMarked episodes of extreme amounts of activity for extended time
Aggression, destructionUnprecipitated violent actions directed to others and the environment
StuporProlonged period of total immobility, lack of responsiveness and mutism
RitualsObject-related actions on objects as part of a routine, repeated event
Motility changese.g., Toe-walking, skipping, hopping
Changes in speech behavioure.g., Mutism; question repetition; echolalia; verbigeration; logorrhea; foreign accent; changes in prosody; difficulty modulating volume
Automatic changesChanges in typical autonomic functions, e.g., heart rate, perspiration, breathing, core body temperature
Table from Autism: Sensory-Movement Differences and Diversity by Donnellan & Leary

Oh! Well, that explains it.

When we look at the characteristics of autistic people from the “movement perspective,” what do we see? What explanations can we come up with? Let’s go through a few of them:

Eye contact

One of the hallmark characteristics of autism is a lack of eye contact, and many autistic people have discussed how they find eye contact uncomfortable at best and painful at worst. We tend to emphasize the sensory aspects of eye contact, but the motor aspect is important, too!

To make eye contact, we must be able to reliably control the movement of our eyes. Many autistic people simply can’t do that. In the same way that our eyes reflexively look away from the sun, we might reflexively look away from other eyes. 

Why? Well, making eye contact, especially while speaking, is a resource-intensive task — for everyone, not just autistic people. A 2016 study explored this phenomenon, hypothesizing that eye contact shares neurological resources with verbal processing.

Facial expressions

Another characteristic of autism is the seeming lack of facial expressions… reflexive movements in our faces in response to our environment and to our feelings. 

When neurotypical children develop, they observe and imitate the behaviours of people around them, including the facial expressions of their culture. These people get very good at picking up subtle hints about emotions on other peoples’ faces, particularly in cultures where people are encouraged to make eye contact when socializing. Those same people, however, find themselves misinterpreting the feelings and intentions of autistic people or alternately pathologizing autistic behaviour as a “social deficit.”

Autistic people may not smile as widely, or at all, or may even smile too much. We may never look sad, or we may always look sad. Our facial expressions might be delayed, or they may seem socially inappropriate for the context. It’s common for people to interpret these differences as the person not understanding, but facial expressions, too, are motor-based.

Autistic inertia

“Inertia” is a physics term, describing how a thing cannot change its course of action until affected by an external force. (The term itself is inherently about movement!)

Among autistic people, “autistic inertia” describes how we often get “stuck” and have difficulties transitioning to something new. Once we are doing something, it is hard to stop; once we have stopped, it’s hard to start again.

Some self-advocates may think of this in terms of more complex motor movements. For example, my roommate made me food, which is sitting next to me untouched because I am very focused on writing this article.

It’s important to recognize, however, that many autistic people have difficulty intentionally starting and stopping more basic movements, like pointing or standing up. It’s similarly important to understand that someone’s ability on one day and in one context may not reflect their ability every day in every context. 

Other characteristics

I was surprised to realize how many characteristics of autism are movement-related. It shouldn’t have been a surprise — it just seems so obvious — but sometimes you are unable to conceptualize something until someone else points it out.

To me, it seems clear that many other “autistic” characteristics might be better explained as a result of neurological movement differences. Stimming, toe-walking, self-injury, vocalizations, echolalia, hyperactivity, and impulsivity are all recognized as motor-based neurological differences (…just not in autistic people, for some reason).

Other sensory-movement disabilities?

The table above lists “symptoms” that are characteristic of other neurodivergent conditions, like ADHD and OCD. These, too, appear to have sensory-motor components to them that have yet to be explored.

Further, there are clear differences in how sensory-movement characteristics present in developmental disabilities and in acquired disabilities. In other words, people who have had sensory-movement differences their entire lives grow up with different experiences and develop abilities, strategies, and coping skills that are not the same as people who acquire those differences. 

For example, dyspraxia is recognized by some professionals as a sensory-based motor disorder that is developmental in nature. Looking into dyspraxia, you’ll find some cognitive similarities that are also observed in autistic people, e.g., the tendency to take language literally. 

This may not appear directly related to sensing or moving, but the overlapping characteristic could suggest that people who experience sensory-motor differences may develop in such a way that they assume a literal interpretation of language. Perhaps being overwhelmed by sensory input leaves us less able to interpret nuance.

What do we do with this information?

Hopefully, we start talking about it. Simply recognizing that we have differences in how we move is the start of accommodating ourselves and suggesting accommodations for others.

Many advocates (including myself) publicly campaign for access to effective communication for nonspeaking autistic people. Now that I am aware of sensory-movement differences in autistic people, I believe that most of us are capable of literacy with the right accommodations, and I don’t believe anyone should be satisfied with picture-request systems.

There are only a few assistive technology services that recognize the possibility that nonspeaking autistic people lack speech not because they lack understanding, but because they lack the necessary motor skills.

When it comes to communication for autistic people, these training methods (e.g., Facilitated Communication, Rapid Prompting Method, Spelling to Communicate) have been subject to misinformation campaigns about their efficacy, particularly from the field of behavioural analysis, with some going so far as to claim that these methods have been “debunked” and that people who spell or type independently are not moving autonomously. These same critics often claim that the concept of sensory processing differences is similarly “pseudoscientific,” even though sensory differences are broadly recognized as a characteristic of people on the autism spectrum.

These skeptics may claim that they require more robust evidence, but I believe they are unwilling to examine the existing evidence simply due to cognitive dissonance. The new information doesn’t fit with what they personally believe, and so it must be rejected.

After all, who wants to believe that they have spent decades treating nonspeaking people as incapable of understanding when, in fact, they could do so all along?

Does anyone really want to acknowledge that what we called “autistic behaviours” and claimed to be willful misbehaviour could actually be unintentional, impulsive, and reflexive reactions by their nervous systems?

How many hours have we wasted modifying the automatic behaviour of autistic people when we could have been teaching them how to build intentional motor skills and regulate their nervous systems?

Most importantly, how do we intend on addressing the collective trauma experienced by autistic people, especially nonspeaking people, caused by years of misinterpretations by professionals who still refuse to listen? How will we make up for the years of appropriate education they have been denied and opportunities that they have been excluded from?

Just a few things to think about.

In short, I am hopeful that this conceptualization of autism becomes more widespread. We’re on the cusp of a breakthrough in understanding.