Sensory Processing Disorder, also known as Sensory Integration Dysfunction, is a fancy way of saying the brain does not correctly process information from the senses. Like autism itself the severity of sensory integration dysfunction varies from one child to the next. Let's start from the top.
The 5 senses are our abilities to touch, smell, see, hear, and taste. Children with autism will often be over sensitive or under sensitive in one or more of these areas. The technical big words people like to use here are hypersensitive and hyposensitive. They are opposites of each other. You could just as easily remove "Hyper" and put "Over" in its place. You could also remove "Hypo" and substitute "Under". I know autistic children who exhibit many forms of sensory integration dysfunction including my own son.
Braden is hyposensitive to some types of touch and hypersensitive to taste or texture in his mouth. How do I know that? Let's start with his issues of touch. By observing his behavior I've noticed that Braden craves "input" or stimulation via touch in select situations. It usually occurs when we are outside the house. Braden will go out of his way to stomp on grates, storm drains, or anything else on the ground that has an interesting texture. He'll do this repeatedly. If we're walking in a parking lot my son will spot the big round cap on the sewage entrance and will begin to head straight for it. He just wants to jump on it. Somehow that gives him a sensation he needs to feel. I stomp on it and I feel nothing.
I know another child who is hyposensitive to touch to the extent that he craves pressure on his body. This is relatively common with autistic children and Dr. Temple Grandin invented the squeeze machine to specifically address this. The child I'm referring to absolutely LOVES to have someone lay on top of him and basically squish him. He also loves to be on your back, like a piggyback ride, and have you backup into a wall. He needs that extra input because he has sensory integration dysfunction as part of his autism. A weighted vest or weighted blanket may serve this child well because those products are designed to put added pressure on the body.
Other children may be hypersensitive to touch and may avoid pressure on their body. This explains why "avoiding affection" is one of the symptoms of autism. A child who is hypersensitive to touch will not welcome a nice warm hug.
Braden's texture issues with taste are different. It has taken us a long time to desensitize him in this area. Desensitizing is the process of gradually getting him accustomed to something that he is hypersensitive to. In Braden's case, taste and texture of foods. With the advice and help of a good Occupational Therapist my son is now at a point where he'll reluctantly try any food once. Every now and then he discovers that he likes something new!
How did we discover that Braden was hypersensitive to taste/texture? First, we knew he had sensory integration dysfunction in other areas so we were on the lookout. For a long time Braden ate only liquified foods. As his parents we knew he could chew and eat foods that weren't liquified but he refused to do it. He wouldn't eat anything unless it was liquified. Even if he liked peaches liquified he would not eat them in small pieces, so we knew this wasn't an issue of simply not liking the taste. When we forced him to try a bite of the peaches he always did one of two things. Either he would spit it out or he would swallow without chewing. Both behaviors were strategies to get the peaches out of his mouth as soon as possible. That's when we knew this was a texture issue.
Many autistic kids are overwhelmed in large grocery stores or shopping malls. My son is not one of them. But I know it's common for children with autism to be hypersensitive to those environments. Those children are receiving too much stimulation via sight or sound (aka visual or auditory) or both and it can cause them to act out with inappropriate behaviors like meltdowns or screaming fits. My son Braden doesn't have a problem in those environments. However, he is hyposensitive to sound. He craves it sometimes. In fact, he often makes a sound like "ehhhhhhhhhhhhhhh" and flaps his hands.
The hand flapping isn't like a bird beating its wings. It's more like moving his hands quickly in front of his face. Sometimes like a bird, but usually like a boy who just wants his hands and arms to move quickly. Is this a visual thing? Or is it a need to feel the motion? Only he knows for sure. Either way it is definitely due to sensory integration dysfunction.