Here’s the second post in our series on sensory processing.

In our first post, we described typical sensory processing and explored some of the ways in which difficulties with sensory processing impact a range of daily activities in the life of child. In this post, we explore the individual sensory systems to give you a more detailed view of what’s going on ‘behind the scenes,’ to help you identify and alleviate processing problems.

Before we start…

…let’s remind ourselves of what sensory processing is in a nutshell:

Sensory processing is the ability to take in information through individual sensory systems, put all that information together, make sense of it, and then respond in good time or ignore it.

Getting to know the individual sensory systems

We need to understand sensory processing before we can use it effectively to improve the lives of children and adults who experience sensory processing difficulties. It’s vital to understand sensory processing if you want to change it. I’ve found that, both professionally and personally, the greater my knowledge and experience of sensory processing, the better I’ve become at identifying and treating sensory processing difficulties — in myself and others.

Most of what happens as we process and use sensory information goes on behind the scenes, in the nervous system and the brain. The way we gather, store and are able to retrieve this information once it reaches the brain creates our experience of the world. Sensory processing is the foundation for building the skills we need to be successful. Amazing stuff!

Let’s take a closer look at the individual sensory systems and how sensory information helps to shape our unique experiences. Then we’ll look at examples of how the systems work together. Armed with this knowledge, we can create effective plans to help your child or you begin improving sensory processing.

The balance/movement (vestibular) system

The vestibular system is located in the inner ear and is often called the balance system. This system helps us to stay upright. It is most engaged, with other areas of the brain, when we are standing still!

Information from the system tells the body where the head is in space and in relationship to the ground. There is a lot of important stuff in our heads and we need to protect it. As we move through space, the vestibular system coordinates with information from the eyes, ears and muscles to make sure we don’t splat onto the floor and damage all that precious stuff.

The vestibular system also plays a part in processing information from the other sensory systems it works so closely with. One of its most important functions is to act as a filter and inhibit or ignore extraneous information. More than 2000 bits of information are gathered by the senses every second. Just imagine how overloaded we would become if all that information flooded the brain. We would be overwhelmed and exhausted.

Humans are one of the very few species that stand upright; some believe that is what gave us our edge and enabled early people to become dominant in every landscape. It is an important skill which enables us to remain safe in our surroundings. Once we feel safe we can begin to explore. Although our world has changed significantly, our vestibular system performs the same job as it has always done.

The body position (proprioception) system

In order to stay upright, take action or run away, your brain must know where your body is. Information about body position comes through the joints, muscles and ligaments — AKA the proprioceptive system. This system tells us where our body is in space without using vision. So, we don’t need to look at a body part to know where it is and what it’s doing. Children with poor proprioceptive feedback often look at the body part they are using.

Proprioception helps us refine our movement and control actions like grasping a pencil and applying the right amount of pressure. Information from the joints, muscles and ligaments feed back into the brain and we are able to change the amount of muscle tension and change the position of the joint. As that process happens, over time, we get better at the tasks we practice.

The tactile (touch) system

The skin is known in sensory circles as the tactile system. The skin is the largest organ of the body and has many functions. Perhaps the most obvious is the skin’s job as a barrier — it keeps the good stuff in and the bad stuff out!

Processing tactile information is also an important part of setting and maintaining appropriate boundaries, both physical and social. Information from the skin helps us get a sense of where we stop and the world begins. Together with information from the vestibular and proprioceptive systems, this gives us our physical concrete sense of self on which more abstract concepts are built.

The skin is a complex organ with 15 different types of receptor that help to protect us by registering information from pain, temperature and pressure receptors. Other tactile receptors allow us to explore the world around us by processing information about the texture, shape and size of objects. There are receptors all over the skin but they are more concentrated in certain areas, such as the finger tips, lips and around the mouth, the neck and the genitals.

The visual (seeing) system

As with the other sensory systems, vision has two main functions: protection and exploration through engagement. Information comes in through the eyes and is perceived in the area at the back of the brain called the occipital lobes.

We use our eyes to scan the environment to look out for potential dangers. The eyes take our safety perimeter far away from the body, to allow us plenty of time to react to potential danger. When we feel safe, our eyes can help us to explore and build skills.

The eyes process about 80 percent of the information presented to a school-aged child. That’s a lot!

We talked briefly about the relationship between the vestibular system and the eyes — let’s take a closer look:

  • The vestibular system monitors head position and works with the proprioceptive system to make adjustments so we can use both eyes together effectively.
  • Visual information also supports balance; anyone who has tried to balance with their eyes closed will understand that visual information supports the vestibular system when we are on one foot. We are on one foot quite often when you think about it when we are walking or running.
  • The vestibular system helps to stabilize the image we are looking at when we are moving, so the image is not wobbly or blurred — an important function for both safety and exploration

The hearing (auditory) system

Hearing is the safety system that protects us at the greatest distance. You can hear things like an airplane or an approaching car before you see them. Our ears never close; they are monitoring for the sound of potential danger even when we are sleeping. Children or adults with disruption in the processing of sound often have difficulty getting a full night’s sleep.

Our auditory system processes sounds in the environment and the sounds of language and communication and gives us a sense of space and time. We can tell the size and shape of a room, whether the surfaces are hard or soft, and if there are people in the space, with our eyes closed. We do that by processing how sound bounces off and is absorbed by the objects and surfaces in the environment. The amount of time it takes for the information to travel gives us a sense of time and space. Aren’t our ears amazing?

Information from the vestibular and proprioceptive systems keeps your head aligned so you can use both ears together. Integration of sound from both ears helps give us a sense of midline (the middle of the body) which is important for the skilled use of both sides of the body in a coordinated way (AKA bilateral coordination).

The taste (gustatory) and smell (olfactory) systems

These two systems work closely together to help us stay safe in the environment and enjoy unspoiled nourishing foods. Anyone who has had a cold knows that when your nose is stuffy your food tastes bland. Information from the taste buds must be combined with information from the ‘smells file’ of the olfactory system to give us the full perception of taste that we actually experience.

Taste and smell are closely linked to feeding. Children who experience problems processing taste and smell often have problems around food and/or meal times. (This is a complex subject — and a source of anguish for families and therapists alike — which we’ll discuss in a separate blog post.)

The taste (gustatory) system

The gustatory system is made up of taste sensors (taste buds) in the mouth and on the tongue. The average person has about 5,000 taste buds. A sensitive person can have more than 20,000! The gustatory system is responsible for detecting flavors, the main five being sweet, salty, sour, bitter, and umami (glutamate). Information from these taste receptors is transmitted to the brain via three cranial nerves including a facial nerve. That’s why children and some adults make funny faces when new foods are introduced!

The smell (olfactory) system

The olfactory system is made up of the external and internal nasal cavity, which directs smells to the olfactory nerve as we breathe in.

There are thousands of different odors and, as we’ve seen, they enhance our enjoyment of food and drinks. But odors also protect us from ingesting noxious substances and non-food items — because we smell things before we taste them!

As a child gathers smell-related information from the world around him, he begins to build his ‘safe’ and ‘NOT safe’ memory smell files. If familiar odors, including foods, register as NOT safe, the child may respond with extreme reactions such as gagging or vomiting. This mis-filing can lead to a child having a limited repertoire of liked foods — and significant difficulties around meal times.

Smell information is transported to the brain by the olfactory nerve which is located at the top of the internal nasal cavity. The top of the nasal cavity is also the floor of the mid-brain (AKA the limbic system). The limbic system is an area of the brain that is important in emotional regulation, learning and memory. Smells are closely linked to emotions and can trigger strong emotional responses. Problems processing smell information can impact mood and emotion, memory and recall. (For more information about breathing and its link to emotional regulation, look out for our upcoming blog.)

How the sensory systems work together in our everyday lives — using fine motor skills

As an occupational therapist, I work with lots of children who have fine motor difficulties and/or feeding problems. These are areas that may be treated as an isolated skill deficit but are often the result of complex difficulties including sensory processing problems.

Handwriting is a good example of a fine motor skill. Children who are having difficulty with writing are typically referred to occupational therapists. Let’s look at how the different sensory systems are used in accomplishing this skill:

Tactile information from the fingers and the palms of the hands helps us to develop fine motor skills. We can discriminate the texture, size and shape of an object, whether it is soft or firm, warm or cold, etc.

To manipulate an object like a pencil, though, we must also receive feedback from the proprioceptors which help us to exert the correct grip strength and make the adjustments needed to shape and size the letters correctly.

The vestibular system is also a vital part of building fine motor skills like writing. To perform fine motor activities effectively, we must have:

  • Stability in the trunk, shoulders, elbows and neck,
  • Flexibility in the wrists and hands,
  • A stable visual image, and
  • The ability to make small precise eye movements.

Information from the vestibular system enables the body to stabilize and maintain a static position so we can use our hands skillfully away from the body. This is the ideal position for looking at what we are doing, especially when we are learning something new, and for moving freely. The small muscles around the eyes control their movement.

Visual processing helps a child:

  • Recognize whether his motor action (writing letters) matches his visual memory of that specific letter.
  • Write his math answer in the correct space and check to see if letters and numbers are oriented correctly.

All of the time the child is working, her auditory system is monitoring for any changes in the sound environment as well as giving her space and time orientation all while listening to and following direction!

Next steps…

  • Read about primitive reflex patterns the role of retained primitive reflexes in the disruption of sensory processing, and their impact on posture and motor coordination.
  • Use the checklists on our Resources page to help you identify problems in specific systems and the home-based strategies you can use to support your child.