30 Frames per Second vs. 60 Frames per Second

1 - A Technical Overview | 2 - Computer Games | 3 - The Human Eye

The Human Eye (and Visual Cortex)

Here is where things get a little interesting, and where we will see that humans can perceive up to 60+ fps.
Light is focused onto the retina of the eye by the lens. Light comes in a steady stream and not pulses (ok, so this is a little wrong, but we are not talking about the dual nature of light, where it acts as both a particle -photon- and a wave). Again, we live in an analog world, where information is continuously streamed to us. The retina interprets light in several ways with two types of cells. Rods and Cones make up the receiving cells for light. Intensity, color, and position (relative to where the cell is on the retina) is the information transmitted by the retina to the optic nerve, which then sends that info to the Visual Cortex for it to be translated to our conscious self (whoa, went from science to philosophy in one step!).
Rods are the simpler of the two cell types, as it really only interprets position and intensity. Rods are essentially color blind, and are referred to as transmitting in black and white. The black and white is not really true, but rather it is just intensity of the light hitting the cell. Rods are also very fast due to the basic nature of intensity. The amount of neurotransmitter released is basically the amount of light that is stimulating the rod. The more light, the more neurotransmitter. Rods are also much more sensitive than cones. How is this proven? We know by microscopic examination of the retina shows that there is a much greater concentration of rods on the outer edges. A simple experiment that you can do yourself is to go out on a starry night and look at the stars out of your peripheral vision. Pick out a faint star from your periphery and then look at it directly. It should disappear, and when you again turn and look at it from the periphery, it will pop back into view.
Cones are the second cell type, and these are much more complex. There are three basic parts to them that absorb different wavelengths of light and release differing amounts of different neurotransmitters depending on the wavelength and intensity of that light. Basically there are three receptors in a cone that absorb red, green, and blue wavelengths of light. Each of these receptors release a different neurotransmitter for the color, with differing amounts of the neurotransmitter depending on the intensity of the wavelength. Purple is a combination of blue and red, so the red and blue receptors would release differing amounts of neurotransmitter, while the green wouldn't release any. This information then passes onto your visual cortex and we "see" purple. Cones are much more inefficient than rods due to their more complex nature. They also are a little slower to react to changes in light and are also not as sensitive as rods (see above experiment). Cones are what largely make up the center of the retina and fovea (focal point of the retina).
The optic nerve is the highway from which information is passed from the eye to the visual cortex in the brain. This nerve is just a pathway, and does no processing on its own. Its bandwidth is actually really huge, so a lot of information can be passed on. Nerve impulses also travel at over 200 mph to the brain, so it is nearly instantaneous for information to be received from the eye (since the optic nerve is only about 2 cm to 3 cm long).
The visual cortex is where all the information is put together. Humans only have so much room in the brain, so there are some tricks it uses to give us the most information possible in the smallest, most efficient structure. One of these tricks is the property of motion blur. We cannot get away from the phenomena because it is so important to the way we perceive the world. In the visual cortex we can theorize the existence of what I call the motion blur filter. Because the eye can only receive so much information, and the visual cortex can only process so much of that, there needs to be a way to properly visualize the world. This is where it gets tough.
Take for example a fast moving object. The faster it goes, the more it blurs (be it a snowflake or a train). Why does this happen? Let's take the example of a snowflake. At any time it has a fixed position in the universe, no matter what speed it goes at (unless it starts to get relativistic, then we go into some strange physics, but something that is not applicable to what we are talking about). Lets say at 5 mph, we see the snowflake in perfect detail as it falls to the ground. Now we hop into a car and go 55 mph. Can we see the detail of the snowflake? No, it is just a streak to us. Has the snowflake changed itself? Of course not. If we had a really fast camera with a fast shutter speed, it would see the snowflake in perfect detail. Now due to the speed in which our eyes/visual cortex can process information, we cannot see the snowflake in detail. A bird such as an eagle would be able to see more detail and not so much of a streak because it only has rods (it is color blind) and the distance from the eyes to its highly specialized visual cortex is 1/16th the distance of ours. This leads to more information being pumped into the visual cortex. So what would look like a streak to us would look like a fast moving snowflake to the eagle.
If we didn't have the ability to produce motion blur, we would see the snowflake pop in and out of existence at high speeds. We would first see it one place, then it would disappear and pop into existence several feet beyond depending on the direction it is going. Is this a good thing? No, we would have a hard time figuring out the direction of the snowflake and have many problems with perceiving movement in three dimensional space. With motion blur we get the impression of continuity where our hardware cannot distinguish fine detail while the object is moving at high speeds.
Contrary to the belief that we cannot distinguish anything over 30 fps, we can actually see and recognize speeds up to 70+ fps. How can you test this? You can quickly do this with your monitor at home. Set the refresh rate to 60 Hz and stare at it for a while. You can actually see the refreshes and it is very tiring to your eyes. Now if we couldn't see more than 30 fps, why is it that flicker free is considered to be 72 Hz (refreshes per second). You can really tell if the refresh is below 72 by turning your head and looking at the screen through your peripheral vision. You can definitely see the screen refreshes then (due to rods being much more efficient and fast).

Conclusion

We as humans have a very advanced visual system. While some animals out there have sharper vision, there is usually something given up with it (for eagles there is color, for owls it is the inability to move the eye in its socket). We can see in millions of colors (women can see up to 30% more colors than men, so if a woman doesn't think your outfit matches, she is probably right, go change), we have highly movable eyes, and we can perceive up to and over 60 fps. We have the ability to focus as close as an inch, and as far as infinity, and the time it takes to change focus is faster than the fastest, most expensive auto-focusing camera out there. We have a field of view that encompasses almost 170 degrees of sight, and about 30 degrees of fine focus. We receive information constantly and are able to decode it very quickly.
So what is the answer to how many frames per second should we be looking for? Anything over 60 fps is adequate, 72 fps is maximal (anything over that would be overkill). Framerates cannot drop though from that 72 fps, or we will start to see a degradation in the smoothness of the game. Don't get me wrong, it is not bad to play a game at 30 fps, it is fine, but to get the illusion of reality, you really need a frame rate of 72 fps. What this does is saturate the pipeline from your eyes to your visual cortex, just as reality does. As visual quality increases, it really becomes more important to keep frame rates high so we can get the most immersive feel possible. While we still may be several years away from photographic quality in 3D accelerators, it is important to keep the speed up there.
Looks like 3dfx isn't so full of it.

1 - A Technical Overview | 2 - Computer Games | 3 - The Human Eye