In addition to information from senses and memory, we also use proprioception, which is the ability to sense the relative positions of parts of our bodies and the amount of muscular effort being involved in moving them. Close your eyes and move your arms around in an open area. You should have an idea of where your arms are located, although you might not be able to precisely reach out and touch your fingertips together without using your eyes. This information is so important to our brains that the motor cortex, which controls body motion, sends signals called efference copies to other parts of the brain to communicate what motions have been executed. Proprioception is effectively another kind of sense. Continuing our comparison with robots, it corresponds to having encoders on joints or wheels, to indicate how far they have moved. One interesting implication of proprioception is that you cannot tickle yourself because you know where your fingers are moving; however, if someone else tickles you, then you do not have access to their efference copies. The lack of this information is crucial to the tickling sensation.
Steven M LaValle 2016-12-31