Proprioception is one of our eight senses, and it is tied quite strongly to our vestibular sense. Our vestibular sense is our sense of balance – it's what stops us from falling over and can be affected by a number of things.. Ear infections are a common cause of impaired balance but this sense can be affected by autism too.
Our proprioceptive sense tells us where our limbs are within space and time, and where our bodies end. It's what allows us to walk without thinking about where our feet are, or more accurately, what allows you to walk without thinking about where your feet are. I have to pay conscious attention to where my feet are when I'm walking if it is unfamiliar terrain. I can, to some extent, automate the process of walking if I know the terrain well or there are no other demands on me, but I must pay attention to where my feet are and what they're doing if I am walking anywhere other than flat ground which is clear of obstacles (like people, trees, street furniture etc.).
It is proprioception that lies at the heart of Simone Biles' “twisties” problem at the Tokyo Olympics. Gymnasts rely heavily on their proprioceptive sense (and indeed, need a well developed one to even attempt the sport) to let them know where they are in the air, which way up they are, and where all their limbs are in order to deploy each one for a safe landing. With a misfiring proprioceptive sense, this is impossible. With time, this misfire can pass and the gymnast is able to perform these impressive movements again. For autistic people, no amount of rest or practice will change the proprioceptive sense although muscle memory can, to some extent, enable us to move around a familiar environment or perform familiar movements (such as those involved in driving) after intense practice.
Autistic people often struggle with motor skills (co-ordination) and can experience issues with gross motor control (such as an inability to catch a ball or handle items) or fine motor control (tasks like threading a needle, or fine painting). We can also exhibit superior abilities in these areas – just like our other senses, we can be hyper- or hypo-sensitive in proprioception. Severely affected proprioception, as well as visual processing problems, is often diagnosed as dyspraxia (another condition under the neurodiversity umbrella).
My proprioceptive sense is affected by shutdowns and meltdowns and can take several days to return fully. During this time I am physically unable to walk in a normal manner, and can only take short, slow steps that are unlikely to result in injury. It's a bit like an old computer restarting in “safe” mode.
It also affects my ability to move and cope when there are multiple obstacles. These obstacles may not be things you would consider to be obstacles, but they are to me. Navigating through woodland where brambles trip my feet and I must dodge low hanging branches and twigs requires superhuman effort on my part and leaves me feeling exhausted and unable to process or cope. To most people, these are not obstacles as they don't require any effort or conscious thought to navigate.
My proprioceptive sense means I cannot cope with being upside down (except when I am not in control, willingly and by choice, on a rollercoaster). Doing a forward roll is an incredibly stressful experience for me, and I have never mastered the tumble turn in the water, despite being a reasonably good swimmer in breaststroke and backstroke (I can't co-ordinate my breathing and limbs well enough to safely do front crawl). In fact, it was through watching the movements of swimmers at the 1992 Barcelona Olympics that I managed to work out the sequence of limb movements required for breaststroke and I have been complimented on my style in the pool.
Observation of others and translation into my own movement is an exercise which takes a lot of time for me. I can't watch someone do a dance move and learn the choreography like many people can because I don't have the same functional ability in my proprioceptive (or visual processing) sense. It took me around 2 years to learn to drive to an acceptable standard because of the need to co-ordinate multiple limbs at the same time to perform certain actions. My problems with ascertaining left and right add another layer to the whole thing, so even taking directions verbally is no better than watching (in fact, it is worse because there's another couple of levels of sensory translation involved). In the two times I have been ice skating I managed to fall over while holding on to the side with both hands, and even skated over my own fingers. That's proof enough that I struggle a lot with some aspects of proprioception.
If we look at the steps involved in sensory processing we can see that proprioceptive impairments occur at every stage of the process. We may not register the sense in the first place, or only register part of the information (such as, my foot is still at the end of my leg, but I don't know where that really is). We may not register the sensory input at all, and jump straight in at the observation stage (oh, my foot appears to be stuck in something). At this point our brains may not interpret and/or action the stimulus and so we never get to the correct action, thereby falling over (my foot, which I think is still at the end of my leg, is stuck but I can't intercept the signals and therefore I become unbalanced and fall over).
Proprioception also makes me appear very clumsy. I can't peel potatoes without dropping them a lot as manipulating strange and non-uniform shapes requires more ability than I naturally have. I frequently accidentally throw items I am trying to pick up because I can't accurately judge the amount of force needed (especially when different amounts are needed in each finger), the direction and the motion. Every time I pick something up without dropping or throwing it requires effort on my part.
I am reasonably good at tasks which require fine motor control, things like painting, sewing and butchery. I am able to access the hyperfocus that comes with being autistic to intensely concentrate on these tasks and perform them to a high degree of accuracy. That's not to say that these things come easily straight away, there's still some practice involved, but it doesn't take me 2 years to master a particular embroidery stitch, or cutting technique. It helps that I enjoy these things and can therefore spend hours absorbed in them quite happily.
So, as is often the case with the other senses, this autistic person has both hypo- and hyper-sensitive aspects to their proprioceptive sense. Nobody can see any of the effort that I am making, nor can anyone see that I find some things distressing and impossible; it would be great if my own account and judgement was universally accepted though, rather than me being challenged and thought lazy or useless just because I have sensory differences that most other people will never be experience or be able to understand.