I read an interesting thought last night; basically, that hearing is the only sense that we don't have to try harder to use - where you can adjust the muscles around your eye to focus better, you can't try harder to hear something. Instead, as the ears are passive sensory organs, you have to quiet your thoughts or move your attention away from your other sensory input to pay more attention to what is there regardless of what effort you make.

So, granted, you can try harder to see something with your eyes, and in a different sense you have to reach out to physically touch something, so I could see that argument. Ok, and yeah, you can physically sniff more to smell something better, and put something in your mouth to taste it. What about the subtler senses, though, like our sense of space or objects-in-space, or our sense of what's happening internally in our bodies (there's a medical term for that, I'll find it)? Are those passive and requiring of attention rather than effort (there's my vote), or are they more active senses?