Do helmets restrict vision?

[sam]

It's as though the helmet blocks the 6th sense.

You've spent your whole life getting by with your head in a particular shape, and the sounds around you being diffracted in a very particular way. Your brain has developed so that it can decode these diffracted sounds very cleverly, constantly and accurately 'placing' things all around you that you didn't even know were there. If you wear a soft hat, it doesn't make much difference as the soft fabric absorbs some of the sounds without changing the pattern. But with a hard, acoustically reflective substance, it changes all of the diffraction patterns. That part of your brain which usually does the work, feels like it is looking at a detuned television set - it is getting a faint picture, and a lot of random noise. Hence, you lose you 6th sense.

Either that, or it's got tin foil inside it.