stretch out your arms in front of you and then slowly move them apart just until you can't see them anymore. isn't this meant by field-of-view? the angle nearly is 180° (horizontally) and this shouldn't vary for humans with full sight.
the problem is you can't use this for camera.arc because the maths of perspective projection works differently than the projection of the eye (probably because the retina isn't flat but spherical?). it will lead to extreme distortions. you would have to use several cameras with lower angles side by side to mimic the human panorama view.
... where does the 55 come from? it's like running around with a binocular. i find something like 75 or 80 looks way more natural.
Humans see far more than 55*, we see nearly 180*. However when the human eye is looking at a monitor, the monitor fills about 55* of vision. So having the games camera view 55* of the world makes it look "natural" and undistorted.
Personally I always run .arc at around 75 or 80. It makes levels feel larger and movement feel faster. But that's just me.