I spent part of this afternoon at a fascinating talk on the sense of touch – one of those things that seem so simple yet have a tremendous degree of complexity when you get into them. (And much of what we know, it seems, comes from when these systems, through illness or injury, go wrong.)<\/p>\n
So what contributes to your sense of touch?<\/p>\n
(a) Meissner’s endings (which sense dynamic pressure, i.e. movement)
\n(b) Merkel’s cells (which are biased towards static pressure, allowing the modulation of your force so you don’t squeeze say a glass to smithereens)
\nThe above are close to the surface, while deeper down are:
\n(c) Pacinian endings (which sense vibration)
\n(d) Ruffini endings (which sense skin stretch)<\/p>\n
Then there’s proprioception, which gives you the sense of where your limbs are. (Why even with your eyes closed if someone moves one limb to a position, you can put the matching one in the same position.)<\/p>\n
Contributors to this are:
\n(a)Muscle spindles (the nerve fibres in which sense position and movements)
\n(b) Golgi tendon organs (muscle tension)
\n(c) Extra-muscular receptors
\n(d) Joint capsule receptors
\n(e) Those Ruffini endings again<\/p>\n
All of these separate pieces of information apparently travel independently to the brain, where they are processed in different areas of the brain (as seen in EM imaging) , so there are “dimensions of touch”, each perceived in a different part of the brain.<\/p>\n
Then there are varying actions for touch<\/b>, which seems to follow from above<\/p>\n
1. Lateral motion e.g. rubbing a finger across the surface, which gives texture
\n2. Static contact – fingers resting on the surface – for temperature
\n3. Enclosure, holding grasping the object – for shape
\n4. Unsupported , holding the object in the hand – for weight
\n5. Contour – tracing around the edges – for global and exact shape<\/p>\n
If you try to use an action to make the “wrong” judgement, it will be highly ineffective.<\/p>\n
Interestingly, the touch part of your brain is very close to the movement part, while sight is much further away.<\/p>\n
However, vision is a holistic sense, while processing of touch happens serially – each one being acknowledged in turn, <\/p>\n
No wonder the robot-makers have so many problems when they try to make their inventions carry a glass of water across a room. (Although looking around this I found one way they are trying to deal with this is to create artificial skin<\/a>.)<\/p>\n