How do you know where your body parts are without looking?

The answer

Proprioception, sometimes called the sixth sense, is the body's ability to sense the position, movement, and force of its own parts without visual input. Specialized receptors called muscle spindles detect muscle stretch, Golgi tendon organs measure tension, and joint receptors signal joint angle, all sending continuous information to the cerebellum and somatosensory cortex. This sense is why you can walk without watching your feet, type without looking at the keyboard, and touch your nose with your eyes closed. The rare condition of proprioceptive loss (as documented in the case of Ian Waterman, who lost proprioception below the neck due to a viral illness) is profoundly disabling, requiring conscious visual monitoring of every movement. Proprioception can be trained and improved, which is a key component of athletic training and physical rehabilitation.