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A simple daily event has amazed me and triggered this question. I have read and heard about hand-eye coordination. It quite straightforward when you e.g. want to open a door or play Xbox. In this case either your hand is in your view or your hand will feel the buttons of your Xbox.

But when it comes to catching a ball or try to catch a falling object, our hand is totally out of our view since we are closely following the trajectory of the moving object. But meanwhile our hands moves in a 3D space and align it self perfectly in the path of trajectory correctly. This is what amazed me.

If you can see your hand and the object/ball simultaneously, its just a matter of moving our hand in the path of that ball/object. But having hands totally out of sight but catching the ball/object perfectly every time is amazing piece of nature's engineering.

How humans have achieved such a amazing piece of coordination in a 3D space without seeing where the hands are located?

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  • $\begingroup$ Body self-awareness? $\endgroup$
    – cagliari2005
    Mar 26, 2015 at 1:11
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    $\begingroup$ sight is not the only sense that tell us how our limbs are moving - otherwise blind people wouldn't be able to move $\endgroup$
    – rg255
    Mar 26, 2015 at 13:40

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Short answer
Proprioceptic receptors provide a feedback mechanism from the body to the brain, telling the brain what our limbs are doing and where they are with respect to the body without visual feedback being needed.

Background
Muscles, skin and joints contain proprioceptic receptors. They sense position and movement of our limbs and trunk, they register force as well as heaviness. Examples of such receptors are limb tendon organs and possibly also muscle spindles, which contribute to the senses of force and heaviness.

Proprioceptive sensations are influenced by visual input, but operate without it. The proprioceptive system is responsible for the ability to touch your nose with your eyes closed and the examples you have given related to catching a ball while not paying visual attention to the position of your hands.

Afferent signals from these receptors are combined and processed in the brain. Together they form information about limb position and movement. This information is mapped relative to a central body map to determine the location of the limbs in space. The proprioceptive senses, particularly of limb position and movement, deteriorate with age and are associated with an increased risk of falls in the elderly.

Reference
Proske & Gandevia, Phys Rev 2012; 92:1651-97

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