Everyone can recall the iconic scene in the movie "Sixth Sense" where Haley Joel Osment whispers to Bruce Willis, "I see dead people." The camera then does a slow close-up of Bruce's face, and everything is all dramatic. While this "sixth sense" is debatable, the other five: sight, sound, smell, taste, and touch, have been established since the time of Aristotle. However, they are far from the only senses we possess; they are just the most evident. In fact, neurologists today are unsure of just how many sense there are, or even exactly what characterizes a sense. One point on which they do agree, is that there are more than five. Among these, I find one, proprioception, to be the most interesting and most deserving of further examination.
The Lilienfeld text gives it but the briefest mention, and defines it simply as, "a perception of our body's location." Not at all exciting, but try this experiment. Close your eyes, and then touch the tip of your nose with your index finger. How did you do that? Your eyes were closed, so how did you know which finger was your index finger? Did you hear the air rushing past your hand as it moved toward your face? Or maybe, somehow smell your hand as it approached your nose? Unless you are in fact a very lame superhero, probably not. It was your sense of proprioception at work.
But so what? This is all trivial. Consider then, that were it not for this sense you would have to constantly monitor your feet to make sure that they are, in fact, still on the ground. Or perhaps, you would need to watch your torso so you don't start walking off in the wrong direction. Evolutionarily, this would have been a huge deal. When confronted with some giant predator in the woods, imagine that instead of running as fast as humanly possible, you also had to make sure you weren't running toward said tiger/bear/dinosaur. You can see then, how those who had a more developed sense of proprioception had a better chance of survival.
Your five primary senses may allow you to interact with the world around you, but proprioception allows you to function as a coherent unit. The ability to interact with the deceased may be discovered one day, but it certainly won't be the sixth sense.