If I asked you to name all the senses, I’m certain you would be able to do so:  sight, touch, hearing, smell, and taste, right? But did you know that there are two more?

We are taught that there are five senses because we are highly aware of them and easily able to see how they affect us. While this method is not incorrect, it is incomplete.

Your five traditional senses are called extero-senses, but there are two more that are called intero-senses. They are sometimes called the "hidden senses" and they are just as important to daily life. These intero-senses are:

• The proprioceptive (pro-pree-oh-sep-tiv) sense, or proprioception, which provides information about your body’s position and the movement of your body’s parts.  This information comes from the muscles and joints.
• The vestibular sense provides information about your body’s sense of balance and the movement of your body through space.  This information comes through the inner ear.      

While these senses may seem to go unnoticed, they are no less important than the other
five. The surest way to know how crucial they are is to observe the effects when they are not functioning properly.

The Proprioceptive Sense

The proprioceptive sense gives us information about how we are moving and where our limbs are in relation to our own bodies.  Proprioception provides body position awareness and aids in motor control and motor planning. Proprioceptive receptors are in the muscles, joints, ligaments, tendons, and connective tissue.   

When you sit in a chair, it is your proprioceptive sense that constantly fires messages to your brain to allow you to remain up right in that chair, to cross your legs, or to sit forward or back in the chair. 

When our proprioceptive system is not working properly, everyday activities such as dressing, sitting up in a chair, or grasping something with the correct amount of pressure can take a tremendous amount of energy and thought.  It can be exhausting.

Common Signs of Proprioceptive Difficulties:

• Difficulty maintaining postures, even while sitting in a chair
• May appear confused as to how to move
• Has a wide stance when standing still
• Uses too little/too much pressure when hugging
• Sits in the "W" position (knees bent in front with legs out to the side, giving a wide base of support)
• Falls or crashes into things purposefully
• Grinds teeth/bites or chews objects
• Preferred motion is short and quick, instead of sustained-endurance activities

The Vestibular Sense

It may be easier to think of this as the balance and movement sense. The vestibular sense lets you know whether you are upright, horizontal, moving, or falling, by receiving stimuli from the force of gravity through the receptors in the inner ear.  Your brain uses that information, trough the nerves and the muscles, to keep you upright.

This sense is so intricate that we may never even think about how it works.  When you tilt your head, how does your body maintain its upright position despite your head’s position?  You can thank your vestibular sense. 

This sense not only tells us when we are moving, but which direction we are moving and how fast we are moving.  It also tells us if the objects around us are motionless or moving.  It allows for our instant and unconscious understanding of our bodies in relation to the things in our environments.

Common Signs of Vestibular Difficulties:

• Avoids playground equipment that involves movement
• Avoids activities that require balance
• Fearful of ascending/descending stairs
• When an infant, arches backward when held or moved
• Clumsy, trips easily
• Avoids feet leaving the ground/uncomfortable in elevators
• Poor sense of rhythm
• Becomes overly nauseated from motion

• As a practical example, these are some of the proprioceptive and vestibular difficulties we noticed with Fiver from an early a
  ge:

• He falls out of chairs, even when properly seated
• He screamed when put on swings or when reclined (such as on changing tables or in the dentist’s chair)
• He screamed during car rides, especially ones that involves any kind of hills/change in elevation
• He does not know the amount of force/pressure it takes to write with a pencil, close a door, open a jar, shake someone’s hand, or hug
• He walks into walls and doors
• He cannot sit in a chair without looking at it first
• He has trouble rolling his body in a specific direction

These are just a few of the symptoms of his malfunctioning hidden senses, and many of these problems have been either improved or resolved through his occupational therapy.

The definitions of the proprioceptive and vestibular senses, as well as the checklists of common signs of difficulty, come from the book The Sensory Processing Disorder Answer Book: Practical Answers to the Top 250 Questions Parents Ask, by Tara Delaney, MS, OTR/L.   Set up in a question and answer format, I found this book very useful for succinct answers to common questions about SPD. 

In addition to appearing here, you can find Aimee managing The HomeFront over at her blog, The Mother Load.