Visual stimuli are measured in frames per second. In other words, when you’re looking around, your eyes are viewing visual cues that move at a certain rate, and that rate is called frames per second.
How many frames per second do you think you can see?
Some experts will tell you that the human eye can see between 30 and 60 frames per second. Some maintain that it’s not really possible for the human eye to perceive more than 60 frames per second.
That might make you wonder why video game developers are making increasingly elaborate games, including virtual reality games, with a much higher frame rate. That’s because we may actually be able to see more than we realized.
First, it’s important to remember how you’re able to see images in the first place.
- Light passes through the cornea at the front of your eye until it hits the lens.
- The lens then focuses the light on a point at the very back of your eye in a place called the retina.
- Then, photoreceptor cells at the back of your eye turn the light into electrical signals, while the cells known as rods and cones pick up on motion.
- The optic nerve carries the electrical signals to your brain, which converts the signals into images.
Reality and screens
When you’re watching a baseball game from the stands, or you’re keeping an eye on a child riding a bike down your sidewalk, your eyes — and your brain — are processing the visual input as one continual stream of information.
But if you’re watching a movie on the television, catching a YouTube video on your computer or even playing a video game, it’s a little different.
We are fairly accustomed to watching videos or shows that are played at a 24- to 30-frames-per-second rate. Movies shot on film are shot at a 24-frame-per-second rate. That means that 24 images flash past your eyes every single second.
But not everything that you see will have that same frames per second rate.
Televisions and computers in your home likely have a faster “refresh rate” that affects what you’re seeing and how you’re seeing it. The refresh rate is the number of times that your monitor updates with new images each second.
If your desktop monitor’s refresh rate is 60 Hz — which is standard — that means it updates 60 times per second. One frame per second is roughly equivalent to 1 Hz.
When you’re using a computer monitor with a refresh rate of 60 Hz, your brain processes the light from the monitor as one steady stream, rather than a series of constant flickering lights. A higher frequency usually means less flicker.
Some research suggests that the human eye may be able to detect higher levels of what’s called “flicker rate” than previously thought.
In the past, experts maintained that most people’s maximum ability to detect flicker ranged between 50 and 90 Hz, or that the maximum number of frames per second that a person could see topped out around 60.
Why do you need to know about flicker rate? It may be distracting if you can perceive the flicker rate, rather than one continual stream of light and images.
You may wonder what happens if you’re watching something with a really high FPS rate. Are you actually seeing all those frames that flash by? After all, your eye doesn’t move as fast as 30 motions per second.
The short answer is that you may not be able to consciously register those frames, but your eyes and brain may be aware of them.
For example, take the 60-frames-per-second rate that many have accepted as the uppermost limit.
Some research suggests that your brain might actually be able to identify images that you see for a much shorter period of time than experts thought.
For example, the authors of a 2014 study out of the Massachusetts Institute of Technology found that the brain can process an image that your eye sees for only 13 milliseconds — a very rapid processing speed.
That’s especially rapid when compared with the accepted 100 milliseconds that appears in earlier studies. Thirteen milliseconds translate into about 75 frames per second.
Some researchers show rapid sequences of images to a person and ask for responses to see what they were able to detect.
That’s what the researchers in the 2014 study did to determine that the brain can process an image that your eye only saw for 13 milliseconds.
An ophthalmologist can examine the movements inside your eye, known as intraocular movements, with high-speed cinematography, to learn more about how rapidly your eyes are operating.
These days, smartphones are even able to capture those subtle movements using slow-motion video. This technology allows the phone to record more images in a shorter amount of time.
As technology evolves, experts may continue to develop new ways to gauge what the eye is capable of seeing.
You may have heard people claim that animals see better than humans. Turns out, that’s not actually true — human visual acuity is actually better than that of many animals, especially small animals.
So, you don’t need to assume that your housecat is actually seeing more frames per second than you are. You can probably see details much better than your cat, your dog, or your goldfish, in fact.
However, there are a few types of animals with very good visual acuity that’s even better than ours. This includes some birds of prey, who can see as many as 140 frames per second.
Your eyes and your brain are doing a lot of work to process images — more than you may realize.
You may not be thinking about how many frames per second your eyes can see, but your brain is using all the visual cues it can to help you make decisions.
As scientists continue to explore, we may learn more about what our eyes and our brains are capable of seeing — and understanding.