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Blobman's avatar

Is the process of human vision comparable to the process of capturing video using a camera (for the purposes of comparing frame rate)?

Asked by Blobman (510 points ) March 17th, 2014

Disregarding the rate at which photons are striking rod/cone cells in the human eye: How quickly does a rod/cone cell react to a photon? How is an electrical signal created to send to the brain and how long does it take to create that signal? How long does it take that signal to reach to brain? After a photon strikes a rod/cone cell how long is it before that cell can react to another photon? Does the electrical signal to the brain carry an entire “image/frame” or just a part of an image that the brain must piece together with other parts? After all of this, what is the “frame rate” of human vision? Is it then dependent on the amount of light in an environment?: Will a decreased rate of photons contacting rod/cone cells change the “frame rate” of vision?

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6 Answers

SavoirFaire's avatar

You might find the background section of this article helpful. This more complicated article would probably help, too. The short version is that the frame rate of human eyes is typically about 10–12 frames per second. Several different parts of the brain are involved in creating the image that we perceive. The early stages of vision generate very rough images, mostly consisting of light maps (“this part is bright, this part is dark”). As the signal passes through the visual cortex, it becomes more and more refined based on this original mapping.

The refining process is restricted by what the brain can deduce from the original input, which is how optical illusions arise. This means that the amount of light in the environment is very important. One of the clearest examples of this dependency is color vision: at night, there is less data for your cones to pick up, which leads to your rods doing most of the work. This is why even a bright red stop sign will seem vaguely grayish until you get close up to it—unless you flash some sort of light on it.

LuckyGuy's avatar

Vision “frame rate” (your term) also varies as we age. Here is how to see it for yourself.
The next time you are driving on the highway at night look at the taillights of a few cars up ahead. Then move your eyes quickly side to side. About ¼ to ⅓ of the cars will have LED taillights that are flashing (strobing) anywhere from 100 Hz to 500 Hz. (I have heard that some cars strobe at 50 Hz. VW? That is very slow and I’ve never seen it.) Can you see the flashing? Some people, usually older adults, can’t see it. Some can see it very clearly. Some see it so well they find it irritating. Ask your young child if they see it. Experiment with a little alcohol. Can you still see the flashing? You might find your peripheral vision sees it better. What evolutionary advantage do you think that offers?

RocketGuy's avatar

@LuckyGuy – the Nissan Leaf uses the same red LEDs for running lights and brake lights. I think the running lights strobe at ½ the rate of the brake lights, based on the moving eye viewing technique.

I can detect strobing using my peripheral vision, up to 60 Hz. The Leaf system runs faster that that.

LuckyGuy's avatar

I’m glad you notice it. You even used the same trick I do – looking at the visual spacing between flashes.
In this day and age, 60 Hz should be considered embarrassingly slow. Why do they do it? Because it saves on the brief switching current and puts fewer cycles on the LED so they will last longer. The real good stuff runs at 5kHz! Yep. (5kHz not 500 Hz!)

Anyone can easily test this speed (up to about 400 Hz if you have a normal optical tachometer) by aiming the tach at the light.

Since you know what I am talking about, try the test with a little alcohol in your system. Just a touch – something that would bring you to 0.01% BAC , well below the 0.08 for DUI. Even at 0.01% you will start to lose the ability to see the strobing. Yet every drunk on the road says they are fine and it doesn’t make a difference – until they are arrested.

I noticed and measured left eye to right eye phase shift of 3 ms using equipment here. Most people do not detect anything below 20 ms.

RocketGuy's avatar

Happy Hour this Thur – now I’ll have to drink beer, then look for a Leaf on the way home.

LuckyGuy's avatar

You won’t need a full hour. Just try half a beer. The result will be depressing.

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