To add to the complexity, scientists now describe some additional senses! We use our Proprioceptive system to evaluate our position in space and in relationship to other people and objects, so we aren’t always crashing into things. We depend on our Vestibular system for balance and coordination. Our Interoceptive system helps us notice and respond to our own internal cues, so (for instance) we know when we need to eat and when we’re full. And Touch turns out be a complicated system that is always working to assess what our body touches, evaluate cues such as temperature and hardness, and notice and immediately respond to pain, which together we call the Tactile system.
The Proprioceptive, Vestibular, Interoceptive and Tactile systems can function differently from person to person.
A child might be "under-responsive" to the Proprioceptive system, so they crave intense physical contact, which seems to ground them. Another child might be "over-responsive" to the Proprioceptive system, so they perceive a tag in their clothing as so irritating that they can’t focus on anything else until it is cut out. In children, this extreme sensitivity can trigger a big enough “fight, flight or freeze” reaction to result in a massive tantrum.
Or a child might be "under-responsive" to the Interoceptive system, so they are less sensitive to their body's cues and don't realize when they need to use the bathroom, which can make potty learning a challenge. Another child might be "over-responsive" to the Interoceptive system, which makes them more responsive to their body's signals, so they experience more pain than another child might from the same skinned knee or shot at the doctor's office.
Every human is unique, but for all of us, Sensory Integration is the process that allows the brain, nervous system and senses (including the Interoceptive, proprioceptive, tactile and vestibular systems) to work together to perceive the world, organize and interpret these perceptions, and respond appropriately.
Difficulties with Sensory Integration in children can show up as Motor issues (dyspraxia, postural disorder), Sensory Discrimination issues (challenges evaluating sensory information such as how forcefully to push something) or, very commonly, Modulation issues (Sensory Seeking, Avoiding or Under-responding). Sensory seeking children seem to crave stimulation, and are always in motion, touching and bumping into things and people. Sensory avoiders over-react to stimulation, sometimes perceiving physical bumps, noise and bright lights as threats. Sensory Under-responders seem not to notice cues, such as their body shivering or a small cut. Parents sometimes have to work harder to connect with children with sensory integration issues, because the usual bonding process of touch can be disrupted and connection between parent and child can be more difficult.
If your child seems to have sensory challenges, the most important thing you can do is offer understanding, so that your child has a parent who partners with them to help them master the challenge. Recognize that the world is a different place for your child than for most children, and offer extra support.
That support will be emotional, but also physical. For instance, all children need to engage physically with the world with messy play and complex movement that stimulate all of their sensory systems, which facilitate healthy sensory development. But kids with sensory issues really crave tactile play. They need play that stimulates all their senses, to give their brains practice integrating their sensory experience.
As many as one in 20 kids has sensory integration challenges. If you suspect that your child might have a sensory processing issue, ask your pediatrician to do a quick assessment. (You can also find checklists online.) Early intervention at the preschool age has the most success since the brain is still forming, but Occupational Therapists who specialize in Sensory Issues are gaining increasing skill in treating sensory issues in people of all ages.