It has really started to appear that people think of sensory processing disorder specifically as a disorder of hypersensitivities. While it is true that hypersensitivities are a part of SPD, they are far from the whole disorder. If you only have hypersensitive senses, you would not fall into the majority of those diagnosed with SPD, or even diagnosed with a sensory modulation disorder.
So, what is a sensory modulation disorder? Those are the cases that you'd probably think of first. Someone's senses are too sensitive. Someone's senses are not sensitive enough. Someone's senses no matter how sensitive they are always needing more input or they just feel wrong and out of their body. These people's bodies don't get the proper amount of sensory input, whether its too much, too little, or just the wrong sort.
All of three of these categories exist here. People with hypersensitive senses exist, and get diagnosed with SPD. These people are getting too much in those senses. It is overwhelming, painful, too much. These are the people who cover their ears when any sort of noise is made, or even start screaming, because its too painful to hear the other noise. They're the people who cut out tags from clothing and otherwise can't wear them. They're the people who the world is too much for.
People with hyposensitive senses exist. These people don't get enough, their bodies don't react with the level of sensory input the world gives them. They might not react to pain, and injure themselves worse because they don't realize they're hurt. They might not be wake-up-able in the morning no matter how loud of an alarm clock you give them, despite the fact that they can hear.
People who just need more sensory information exist. These people seek it out. They crave it. No matter how much you give them, they need more, more, more. They run into things, bouncing off them, and seem made of rubber, as they run off in the other direction, happy. They add the spiciest of hot sauces to every food they eat. They spin whenever given the opportunity too. They always want more.
These three basic kinds of modulation disorders; the hypersensitive, the hyposensitive, and the seeker, are straightfoward. But people aren't that straightforward. What about the person who always wants to spin but any noise they hear hurts their ears? Or the person who doesn't recognize when their name is called, wants squeezed tightly always, and seeing any sort of lights they start getting headaches? People don't always fall neatly into one category. People actually usually don't fall neatly into one category. More people fall into more than one of these three categories than only one.
To make this more complicated, as well as hypersensitive touch, and hyposensitive smell, for example. It is possible to have multiple of these in the same sense. Some items are extremely painful, others are actively seeked out is a common method of this occurring, but it doesn't have to be that simple. It can be "this touch hurts because its too much, but I crave it because without it I don't feel like I know where my body exists", or pretty much any combination you can imagine. They can occur in the same sense at different times, about different items, or at the same time, about the same items. It can present in extremely complicated ways.
However, modulation disorders aren't the only part of SPD. They're the most known type, and the most common type, but, definitely not the only type. Difficulties with discrimination between sensory input, and motor planning difficulties because of improper sensory data also occur.
Sensory discrimination disorder is, I'd guess, the least known part of sensory processing disorder, but a part that can lead to some severe impairments. It's rather getting the wrong amount of information, getting jumbled information. It's not being able to identify what direction sounds are coming from; it's seeing items as the wrong size and the wrong distance away. It's not being able to actually trust what you're sensing because it may or may not be actually true, or not being able to identify what it is that you are sensing.
Sensory discrimination disorder is about not being able to sort out information, not being able to understand the information. It can be extremely difficult to be able to understand what it is like to have this without having it because its so strange to think about someone seeing, but only being able to understand 10% of their vision, and the rest of it being nonsense, or hearing, but hearing things on the wrong side of their head, or tasting, but the food not feeling hot when its burning their mouth... its just wrong data, it being all jumbled up.
Improper sensory information also leads to movement disorders. The body not being able to do what the brain tells it to do can lead to poor motor control, inability to plan out actions, or poor muscle tone and poor balance. The body's sensory system not being able to communicate with itself, makes the body struggle with movement.
Awkward movements, injuring yourself, being unable to ride a bike, being unable to dress yourself without aid, all of these can occur with a motor disorder occurring from a sensory basis rather than any other basis. Choking too frequently on food, having the different body parts not being willing to work together when trying to do a task, again, things which occur.
Sensory Processing Disorder has all of these different components. Some people have one, a modulation disorder, discrimination disorder, or movement disorder, some have two of the three, others have all three. Again, it can combine in any way. All sorts of combinations come out, including people who have every sort of SPD, all three modulation disorders, discrimination disorder, and a movement disorder. SPD can be quite complex.
Which leads us to the other way we can split it up; there are each of our senses. In grade school we are taught there are five senses. This isn't true. There are actually more than five senses. Touch itself is more than one sense, temperature sensing, and feeling a thing just brushing against your skin both fall into "touch" when initially teaching senses, yet are completely different.
For SPD, we tend to think of 8 senses; the five you learn about in grade school, the vestibular sense, propioception, and interoception. The vestibular sense is your sense of balance and spatial orientation. It's that part of your inner ear that tells you whether you are spinning, as well as if you are falling. Propioception is the sense of your body parts knowing where neighboring body parts are. It's your joints understanding their positions, and your fingers knowing where the other parts of the fingers are and how hard to squeeze to pick something up. Both of these senses, are overlooked when describing the senses, but are used every day for interacting with the world.
Interoception is different in that its the group of sensors that tells you about your internal body. It's knowing how hungry you are, how thirsty you are, when you need to pee. It's understanding swallowing, and vomiting. Any of these senses don't necessarily work right either, the information about your internal organs stretching and contracting doesn't necessarily work any better than the external senses does.
All of these different senses, can have any of these different categories of SPD occur. Any of the senses you're used to, the ones you aren't. Things you don't think of as senses, like temperature sensing, or pain sensing. Lots of different options for very individualized descriptions of how its like for individuals.
Because that's what it is, is a very different disorder for every person who has SPD. No two people have the same symptoms. No two people can be treated the same. Every person has their own individualized needs for their own individualized traits. Two people might both have hypersensitive touch, but even then, we can't assume to treat them the same. Everything is about making people understand their bodies needs, and meet their bodies needs. And having others understand those needs and help not cause problems helps immensely there.
If you care to know the numbers used for "most" or such; They're from Sensational Kids by Lucy Jane Miller Ph.D OTR. This book is a good resource on the subject if you want to read more.
- 12% of those with sensory modulation disorder have only hyposensitivity
- 26% have only sensory seeking
- 5% have only hypersensitivity
- 14% have [only] hyposensitivity and seeking
- 15% have [only] hypersensitivity and seeking
- 5% have [only] hypersensitivity and hyposensitivity
- 25% have all three, hypersensitivity, hyposensitivity, and seeking.
- 4% of those with SPD have only sensory discrimination disorder
- 4% have only a sensory based movement disorder
- 22% have only a modulation disorder
- 4% have [only] discrimination disorder and a movement disorder
- 16% have [only] a movement disorder and a modulation disorder
- 23% have [only] a modulation disorder and a discrimination disorder
- 27% have all three, a discrimination disorder, movement disorder, and modulation disorder