In 1998, I went to London for a weekend with my girlfriend. We stayed in a little hotel in Notting Hill and did tourist things for the weekend - a trip to Harrods, a meal in the Hard Rock Café, ...
One of the places we ended up was the Science museum. They had a section full of information about sporting activity, and with little things to play with. You could try virtual snowboarding, or a 100-metre dash with proper electronic timing, or a climbing wall (fun!). And then there was the peripheral vision toy.
Peripheral vision is seeing something out of the corner of your eye, as the expression goes. It's a survival feature, I guess, for a species that's optimised for looking straight ahead. It's mostly very basic - you can detect motion, but you can't make distinctions as to what the motion is. Static things are difficult to see. Your brane tends to treat it a little oddly, almost as if it's a subliminal image or somehow unreal. Well, this is my experience of it, anyway.
An acquantaince of mine once mentioned that peripheral vision is utter pants - he said what actually happens is that your eyes do this high-speed side-to-side glance thing called "saccading". I seem to recall that his referenced proof of this was some study involving dinking with geometrical shapes on screen; apparently the subjects couldn't tell the difference between a circle and a rectangle on screen from sufficiently close range that the circle/rectangle filled their vision. If this sounds incoherent it's because it's been several years since he told me this.
The peripheral vision toy works like this: you sit on a seat partially surrounded by a black wall. At eye-level (the seat's height is adjustable) there's a row of lights running from somewhere over your shoulders all the way around to meet in front of you. You press the "start" button, and the lights switch on in sequence. As soon as you see the lights, you press the "stop" button. Note, as soon as you see the lights without moving your head from looking at a point in front of you. Saccading or peripheral vision, this is a pretty good measure.
I tried it a few times to get an average of some sort. I've always believed I have pretty decent peripheral vision, perhaps to compensate for my screwy eyesight - sort of a karma of vision, if you will. This little piece of gadgetry confirmed that, revealing that I have, apparently, a 200° field of vision - I can somehow see slightly better than 90° to each side of my head. The only thing I can think of to explain this is that there's some form of refraction going on in my lenses. I do notice that there's a blind spot in my peripheral vision around about the 90° point which would seem to confirm this.
It seems to be a little more powerful, too - my colour vision extends a little farther around than you'd expect, to the extent that I can make out roughly what someone's wearing when they're standing beside me.
I'm sure I'll find a use for this, aside from avoiding being run over when I'm cycling around Dublin...