There have been
several threads on this exact topic, if you search for them you should be able to find a fair amount of information.
First off, framerate is only half the problem. Generally, 30FPS is considered the threshold for movement. It is at this framerate that "similar" still images will be stitched together within the brain to give the illusion of fluid movement. However, if the frames are disimilar, the brain cannot as easily stitch them together, meaning that a higher framerate is required for an illusion of fluid motion to kick in. Conversely, if the frames are extremely similar, the brain can stitch them together very easily, and a lower framerate before fluid motion kicks in is required.
So when would these conditions occur? Well, at 30FPS, similar images aren't too hard to come by. You'll see them running down halls, running outside in an open plain, etc. What about times where the frames are disimilar? At 30FPS, significantly different frames will appear when you do quick turns (for example, if you turn the camera 90 degrees in a quarter second [not too hard], each image will differ by 12 whole degrees!).
Even monitor size can have an effect on just how different the frames are. Even though the image will be changed by proportionally the same ammount, a 21" monitor will move each pixel further than a 15" one (at the same distance from the eye), leading to the brain "needing" more FPS on the bigger monitor. If you move the bigger monitor further from the eye though, the screen --and frame differences-- takes up less of our field of vision (which is part of the reason why even 24FPS high movement sequences look good on a movie theater's giant screen)
Also, where the brain's "fluidity limit" is at dosen't stop it from recognizing individual frames. If you insert a totaly different frame (say for subliminal messaging to buy Doom 8 Zillion
) every 30 frames, you brain will pick it up and "see" it. You won't have any idea what you saw (since the brain tried desperatly to stitch it in with the rest of the frames), but your brain did see the image. This occurs even at 60FPS from what I've heard, and probably higher (though I have no reasonable information backing me up).
So basically, framerate means very little, especially when people try to argue that "XXX FPS is enough for anybody!". The eye can "see" a lot faster than 30FPS, and the brain dosen't care how many frames/second you throw at it, so long as each frame is similar enough to the last to stitch together.
JigPu