There have been some very good points made here, and some confused ones. The whole subject of " what the eyes see" is of great interest to me because we spent a long time at Building Panoramics creating a technique called "Eye's View" for our pictures which we generally take of ancient monuments, both preserved and ruinous.
As I said in my earlier post, the eyes do not see. The brain sees. The reason people can have hallucinations, or see ghosts is that the brain sees these things. To the people topping up on magic mushrooms what they see is
real - to them.
The eyes have a field of view, yes, but it is difficult to define as our peripheral vision is a little ill defined - literally. Because a camera ( normally ) takes one exposure with one lens to record a scene, it is in fact very limited when it comes to try and record the view we see, because we are looking around us, subconsciously mapping the info, so our brain then fills in the missing info - a little like the principle of how a tv cartoon works.
You can test this for yourself. If someone takes you into a place strange to you with your eyes closed, and then, once there you open your eyes and look straight ahead you will find out that your actual field of vision is less wide than you have come to accept. Because you have no reference to what is on either side of you your brain cannot fill in the detail to your field of view. it's a bit weird actually, but in a view seconds you will involuntarily glance around.
It the same thing with perspective. People say ' ah-ha, when I look at something really close up I don't get the distortion of an ultra wide lens. No you don't because your brain knows what it should look like, but again you can try and test this for yourself. Find something that sticks out such as a door knob or someone's nose etc. Put you eye right up to it real close, close your eyes and try and empty your brain of though. ( Some will find this easier than others - those who post about 6 million pages etc should find it real easy ). Now open your eyes and look at the object and you may briefly see the very distorted perspective from being so close.
The picture of Beverley Minster below is a good example of this. The nave and transept look like the angle between them is less than 45*, ie V shaped. 'This is perspective distortion from the wide angle lens ' you say. But actually we didn't use a wide angle but a 50mm, shot in our 'eye's view' technique. The V shape is the result of how close we had to be to the subject. When you go and stand there you don't see this V because you know
it's a 90* turn. However if you stand there with your eyes closed, let you mind go blank, and then open your eyes you will see the V before your brain adjusts to correct everything.
Digital has made it possible to replicate how we see things, but it takes a lot of post processing. The picture below was taken using our 'eyes view' technique, which was done by not only stitching, but also exposure and lens focal length stacking to get both the field of view and perspective the same as we see it.
I've added another copy with the 28mm framing added, so you can see just how wide a shot this is, as well as the 50mm framing which was done in various parts of the picture. This takes a lot of work in putting it together. ( Not these focal lengths refer to FF). The result is really like being there.
But to cut to the chase, as others have said: on your APS-c about 30mm will give the perpective as you see yourself, and about a 22mm will give a field of view close to your direct
Hope this is of interest: try and find this on 6 million websites