Monday, November 18, 2013


Touch is not really one sense. It is made up of several different senses which have different nerve endings and different response areas in the brain. In other words, they are processed individually though we lump them all together and call them touch.  These include light touch, deep pressure, heat , cold  and pain receptors. What they have in common is that the nerve endings are spread throughout our skin so we can experience sensation from any part of our body. There are some areas that have a higher concentration of nerve endings and are therefore more sensitive than other areas of the body. Some areas of the body may have more of one kind of receptor than others so may be more sensitive to certain types of touch than to others but in general there are touch receptors all over the body in the skin. Some types of receptors are around the internal organs as well. We all know you can have a stomach ache that is not felt from the skin. All of this is complicated by the fact that you may have different touch sensations at different places at the same time. You mind needs to sort all the sensation and let you decide which is the most important for you to get the information that you need.  If you remember, in the introduction to this series, we used the example of the hot iron to illustrate the sensory motor arc. That example uses the sense of touch, specifically, heat, so you can see how fast your brain can select what you need to know.
The sense of touch is one of the earliest to begin to develop, with some receptors in place by 4 weeks gestation, but it seems to take up to 16 to 20 years for the system to be fully operational.  There are at least 4 different  types of receptors and miles of nerve fibers, as well as the cognitive learning needed to distinguish from what one thing feels like as opposed to another. The fact that you can reach into your purse and find the keys without looking is a testament to the development of your sense of touch.
Simple touch is anything but! The simplest sensation is pressure, but as noted, light pressure and deep pressure are registered differently. Next would come vibration, followed by recognition of different textures, sizes, shapes and spatial orientation, which can all be recognized by touch.  Research indicates that awareness of pressure and vibration is present at birth. Size recognition seems to begin early, perhaps 2-4 months but is on a basic level and need refining. There is some recognition of different textures by 4-6 months which continues to be refined over the next 10 years. The recognition of shape difference by touch may begin after 6 months and there are indications that this, too, continues to develop during childhood.
Early tactile exploration is often by mouth, as this is a very sensitive area for touch stimulation. Manual exploration actually begins around 4 months of age and continues to improve through childhood. The ability to recognize objects by touch is pretty much the same from 15 to about 50 years of age but as with other senses, there is a decline during the aging process,  just as touch is one of the first senses to develop it is the last to decline.

Touch is probably the most pervasive sense we have. It is everywhere in our bodies and is difficult to occlude. Just as development impact the sense of touch (learning shapes, textures etc.), there is ample evidence that touch impacts development.  Studies of infants who were deprived of a chance to use their sense of touch, who were not held or whose physical contact was limited to the crib they were lying in, suggest that this caused global delays that were difficult to make up. Of course, the sense of touch, along with the next two we will discuss, underlies all motor abilities

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