Why can’t we measure the amount of FPS or Hz our eyes run at? What is different from a display to our own “perception”?
In: 92
Because our eyes and brains are analog devices. There’s no “clock” that determines how often they update. They’re just constantly updating in real time. The delay is based entirely on the speed of the chemical and electrical signals.
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Fps and Hz only work in a digital system that sends signals timed to a “clock speed”. Analogue systems (which the eyes are iirc) do not have a frequency because the signals are continuous.
How the eye functions is incredibly complex, both in the eye itself and how the brain interprets the information.
Ultimately, you could establish a “frame rate” for the eye, because it is in a way analogous in effect (not in the physics though) to a camera. Each receptor can only gather a specific amount of light before it’s saturated. The ” maximum frame rate” depends on how fast the receptor can completely recover to zero saturation. I couldn’t find good information on that in the few minutes of search aside from the fact that cones can recover from being flash-blinded in about 20 milliseconds.
https://physoc.onlinelibrary.wiley.com/doi/full/10.1113/JP283105
But these numbers will vary for normal vision, since your eyes don’t get totally blinded.
But that’s just the eye. The brain also has frequencies it works at, i.e. “brain waves”, neurons fire in patterns at certain frequencies to perform specific functions. But this effect is far too complex to assign any one maximum or minimum “frame rate” to it, aside from what we can observe to be true, that at about 24 fps still images start to blur together and you get illusion of motion. But even that isn’t cut and dry, because we are able to see a difference between that and higher framerates. Then there’s the issue of the brain not actually forming a “pixel by pixel” image like a digital display. In trying to interpret the signals coming in it… Makes shit up, effectively. That’s what visual hallucinations are. And how do you apply a frame rate to something that isn’t even a real image from the eyes? (I mean, that’s a genuine question to any neurologists out there, can you?)
To make an analogy. What is the Hz of a compass? Or an old school thermometer?
How often does an analog thermometer update
The answer is that it doesn’t work that way.
Now, there is something to be said about fast eyes can perceive. For example, I notice a big difference between my monitor at 60Hz and 144Hz. So you’re u could argue that my eyes can at least perceive 60Hz. But even so, it’s not a good way to classify it.
The human visual system, which includes both the eye and significant parts of the brain, sort of blend “frames” together. This is why a fast moving fan looks like a constant blur. There’s also considerable latency between when something hits your eye and when you can notice it. Usually 200-300ms.
Other folks have already made the point that FPS isn’t a meaningful concept for human vision. That’s true, but there is another way to think about it. We have something called “persistence of vision”; our brains hold onto a visual stimulus for a short period of time and uses that stored image to make smooth transitions when our eyes move or change focus. We can measure that latency and use it in building displays. In fact, TV and movies only work because of this effect. If you view a video at fewer than 24 FPS, it will look like a series of stills. At frame rates higher than 24 FPS, the images blur together and produce an illusion of smooth motion. Higher frame rates can be more convincing, but 24 per second is the minimum. Taken all together, human vision isn’t a series of stills, but there is enough lag in the system that a frame rate higher than 24 FPS looks like smooth motion and 24 FPS might arguably be seen as an analogous measure of human vision
We do have something called “flicker fusion frequency” which is how many fps are required to make you see it as a continuous thing
I still remember when a crash happened in fornt of my eye, the car and motorcycle both literally stopped for a miliseconds for me.
I’m out and away from my computer, but https://humanbenchmark.com/tests/reactiontime is reasonably good.
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